THE JOURNAL OF BIOLOGICAL CHEMISTRY VOL. 283, NO. 23, pp. 15724 –15731, June 6, 2008
© 2008 by The American Society for Biochemistry and Molecular Biology, Inc. Printed in the U.S.A.
A Kinetic Analysis of Regiospecific Glucosylation by Two
Glycosyltransferases of Arabidopsis thaliana
DOMAIN SWAPPING TO INTRODUCE NEW ACTIVITIES *□
S
Received for publication, March 12, 2008, and in revised form, March 28, 2008 Published, JBC Papers in Press, March 31, 2008, DOI 10.1074/jbc.M801983200
Adam M. Cartwright‡1, Eng-Kiat Lim‡, Colin Kleanthous§, and Dianna J. Bowles‡2
From the ‡Centre for Novel Agricultural Products and the §Department of Biology, University of York,
York YO10 5DD, United Kingdom
The glycosylation of small hydrophobic molecules is known
to alter their chemical and biological characteristics. The alterations include changes in water solubility, stability, pharmacokinetic properties, and bioactivity (1, 2). Enzymes that catalyze
these reactions are Family 1 glycosyltransferases (GTs),3 with
representatives found in a wide range of prokaryotic and
eukaryotic organisms.
* This work was supported in part by the Garfield Weston Foundation for the
Centre for Novel Agricultural Products. The costs of publication of this article were defrayed in part by the payment of page charges. This article must
therefore be hereby marked “advertisement” in accordance with 18 U.S.C.
Section 1734 solely to indicate this fact.
□
S
The on-line version of this article (available at http://www.jbc.org) contains
supplemental Figs. S1–S4 and Tables S1 and S2.
1
Supported by a Biotechnology and Biological Sciences Research Council
studentship.
2
To whom correspondence should be addressed. Tel.: 44-1904-328770; Fax:
44-1904-328772; E-mail: djb32@york.ac.uk.
3
The abbreviations used are: GT, glycosyltransferase; UDPG, uridine diphosphoglucose; HPLC, high performance liquid chromatography; GST, glutathione S-transferase.
15724 JOURNAL OF BIOLOGICAL CHEMISTRY
Extensive study of GT activities has demonstrated that the
enzymes display an exquisite regio- (3), enantio- (4), and chemospecificity (5) toward the acceptor molecule. However, as
yet the determinants of this specificity are poorly understood.
This lack of understanding presents challenges to the interpretation of substrate activity data (6, 7), GT rational redesign (8,
9), and activity prediction (10, 11). Future progress in predicting GT sequence-structure-activity relationships will depend
on a greater number of studies that characterize the key determinants of activity and specificity.
Quercetin is the most abundant flavonoid in the human diet
(12) and has frequently been used as a model substrate for GT
activity (13–15). Quercetin aglycone is found only at low concentrations in the primary dietary source, plants, where glycosylated forms predominate (16). In addition, in mammals, glycosides are the major byproducts of quercetin phase II
metabolism (17). Many studies have shown that glycosylation
of quercetin significantly affects bioavailability and efficacy
with respect to anti-oxidant, anti-proliferative, and anti-cancer
properties (18). There are also some data to indicate that the
position of glycosylation can affect bioactivity (19 –21).
Many plant, animal, and microbial GTs can recognize quercetin as an acceptor when assayed in vitro. Although certain
enzymes show some specificity toward individual hydroxyl groups
of the aglycone, others can glycosylate multiple hydroxyl groups.
For example, the model plant Arabidopsis thaliana contains 107
GT open reading frames that glycosylate a broad range of acceptors in vivo and in vitro (1). The study of Lim et al. (3) revealed the
range of A. thaliana GT activities toward quercetin. Some GTs
such as UGT78D2 and UGT71C2 glycosylated only the 3-OH or
7-OH positions, respectively, whereas other GTs, such as
UGT88A1, were capable of recognizing multiple positions.
To date, analyses of GTs that form multiple monoglycosides
of quercetin have typically relied on product formation profiles to give an indication of regiospecificity (22, 23). This
provides limited information because the underlying kinetic
parameters for each glycosylating reaction are masked by the
single reaction condition used to generate the product formation
profile. This limitation is equally applicable to studies of GT regiospecificity toward acceptors beyond quercetin.
In this study, a domain-swapping strategy of two highly
related A. thaliana GTs, UGT74F1 and UGT74F2, has been
used to explore the basis of their differing regiospecificity
toward quercetin. A high performance liquid chromatography
(HPLC)-based kinetic analysis has been established to analyze
VOLUME 283 • NUMBER 23 • JUNE 6, 2008
Downloaded from http://www.jbc.org/ by guest on June 24, 2016
Plant Family 1 glycosyltransferases (GTs) recognize a wide
range of natural and non-natural scaffolds and have considerable potential as biocatalysts for the synthesis of small molecule
glycosides. Regiospecificity of glycosylation is an important
property, given that many acceptors have multiple potential glycosylation sites. This study has used a domain-swapping
approach to explore the determinants of regiospecific glycosylation of two GTs of Arabidopsis thaliana, UGT74F1 and
UGT74F2. The flavonoid quercetin was used as a model acceptor, providing five potential sites for O-glycosylation by the two
GTs. As is commonly found for many plant GTs, both of these
enzymes produce distinct multiple glycosides of quercetin. A
high performance liquid chromatography method has been
established to perform detailed steady-state kinetic analyses
of these concurrent reactions. These data show the influence
of each parameter in determining a GT product formation
profile toward quercetin. Interestingly, construction and
kinetic analyses of a series of UGT74F1/F2 chimeras have
revealed that mutating a single amino acid distal to the active
site, Asn-142, can lead to the development of a new GT with a
more constrained regiospecificity. This ability to form the
4ⴕ-O-glucoside of quercetin is transferable to other flavonoid
scaffolds and provides a basis for preparative scale production of flavonoid 4ⴕ-O-glucosides through the use of wholecell biocatalysis.
Regiospecific Glucosylation by Two A. thaliana GTs
the parameters of kcat and Km for each glycosylation reaction of
the GT toward the different hydroxyl groups of quercetin.
Interestingly, the generation of the UGT74F1/F2 chimeras
produced a novel preference for glycosylating the 4⬘-OH of quercetin. Although all chimeras can produce 4⬘-O-glucoside, one
shows a high specificity for the 4⬘-OH. The individual amino acid
responsible for the observed shift in specificity toward the 4⬘-OH
of quercetin has been identified and its influence on regiospecificity toward other flavonoid substrates analyzed.
JUNE 6, 2008 • VOLUME 283 • NUMBER 23
RESULTS
Regiospecificity of UGT74F1 and UGT74F2 toward Quercetin—
A. thaliana GTs UGT74F1 and UGT74F2 share 76% sequence
identity and 90% similarity at the amino acid level and are predicted to share an identical secondary structure (Fig. 1). The
activities of the two GTs toward the flavonoid quercetin
JOURNAL OF BIOLOGICAL CHEMISTRY
15725
Downloaded from http://www.jbc.org/ by guest on June 24, 2016
EXPERIMENTAL PROCEDURES
Materials—Chemicals and reagents were obtained from Sigma-Aldrich unless stated otherwise. Glutathione-Sepharose 4B
was purchased from GE Healthcare and oligonucleotides from
Sigma. 3⬘4⬘7-Trihydroxyflavone, luteolin 4⬘-O- and 7-O-glucosides, kaempferol 7-O-glucoside, and apigenin 7-O-glucoside were purchased from Extrasynthese (Genay, France).
Site-directed Mutagenesis—Site-directed mutagenesis was performed by a whole plasmid method based on that of Hemsley et al.
(24). Mutations were confirmed by DNA sequencing. Overlap
extension PCR (25) was used to create mutant F22221. A full list of
oligonucleotides is provided in supplemental Table S1.
Protein Expression and Purification—All proteins were
expressed from the pGEX-2T vector as GST fusion proteins in
Escherichia coli strain BL21 (DE3). Briefly, this involved culturing cells at 20 °C until late stationary phase (A600 ⬎ 2.0) and
then inducing with 1 mM isopropyl-1-thio--galactopyranoside at 20 °C for ⬃16 h. Cells were lysed by osmotic shock, the
lysate clarified, and the GST fusion protein purified using glutathione-Sepharose 4B. Elution from the affinity matrix was
achieved by washing twice with an equal bed volume of 100 mM
Tris-Cl, pH 8.0, 20 mM reduced glutathione, 120 mM NaCl.
The GST fusion partner was cleaved for thermal denaturation studies. Replacing the elution steps, the Sepharose-enzyme pellet was washed with thrombin cleavage buffer (20 mM
Tris-Cl, pH 8.4, 150 mM NaCl, 0.25 mM CaCl2) and then incubated with 10 units of thrombin (Sigma) for 120 min at 25 °C.
Cleaved GTs were found to be ⬎97% pure by SDS-PAGE analysis (supplemental Fig. S1) and displayed an activity equivalent
to the GST fusion (data not shown). Protein concentration was
determined using the Bio-Rad Quick Start Bradford Dye Reagent (1⫻) calibrated using amino acid analysis (Alta Bioscience,
Birmingham, UK).
Glycosyltransferase Activity Assay—For kinetic analysis a
50-l volume comprising 100 mM Tris-Cl, pH 8.0, 7 mM uridine
diphosphoglucose (UDPG), 4 –200 m quercetin, and 0.2–2 g
of enzyme was assayed at 30 °C for 0.5–10 min and then snapfrozen in liquid nitrogen. Prior to HPLC analysis the sample
was thawed, and 5 l of trichloroacetic acid (240 mg/ml) was
added and then centrifuged at 13,000 ⫻ g for 10 min. Reversephase HPLC analysis (Waters 2695 separations module with a
486 absorbance detector) was performed on a 5 C18 column
(Phenomenex) with a 24 –59% acetonitrile gradient over 10
min; all solutions contained 0.1% trifluroacetic acid. Spectra
were recorded at 370 nm. GT activity toward additional flavonoid substrates was assayed under the same conditions
except that a single time point was analyzed, a single flavonoid
concentration (200 M) was used, and HPLC analysis utilized a
10–75% acetonitrile (0.1% trifluroacetic acid) gradient over 20
min.
To qualify for kinetic analysis by pseudo-single substrate
assumptions, the following criteria were defined for all reactions: 1) the other co-substrate in excess, namely UDPG (7 mM,
7–14 ⫻ Km wild-type parents) or quercetin (200 M, 4 –50 ⫻
Km wild-type parents); 2) the combined amount of product did
not exceed 15% of initial substrate concentration; 3) no diglucoside was formed. UGT74F1, UGT74F2, and all mutants can
form quercetin diglucosides; their presence indicates product
inhibition/competition between the quercetin aglycone and
monoglucoside product.
Thermal Denaturation Profiles—Recombinant protein, lacking the GST fusion, was dialyzed against 10 mM phosphate
buffer, pH 8.0, at 4 °C. Samples were taken to a concentration of
0.24 mg/ml and analyzed on a JASCO J810 CD spectrophotometer with a JASCO PFD-425S Peltier system. Measurements
were taken at 220 nm with a data pitch of 2 °C, 1-s response,
1-nm bandwidth, and temperature slope of 2 °C/min. Mean
residue weight was calculated according to Kelly et al. (26).
Whole-cell Biotransformation and Flavonoid Glucoside Purification and Identification—Whole-cell biotransformations
were performed in 1-liter shake flask cultures of E. coli BL21
(DE3) harboring the appropriate GT in a pGEX-2T vector. Cultures were grown at 28 °C, 150 rpm, in M9 minimal medium
containing 0.4% glycerol and 50 g of ampicillin to A600 0.75
and then induced with 0.1 mM isopropyl-1-thio--D-galactopyranoside and incubated for 16 h. Following the induction
period, 10 mg of quercetin was added (time point zero). A further 10 mg of quercetin was added at 7, 27, and 31 h. Additional
glycerol was added to the cultures, to a final concentration of
0.15% (v/v), at 4, 7, 25, and 31 h. The E. coli culture was centrifuged and vacuum-filtered before application to an Amberlite
XAD-2 column (30-ml bed volume). Fisetin glucoside and
quercetin glucoside were eluted from the column with 10 and
20% isocratic acetonitrile gradients, respectively. The fractions
containing the glucoside were pooled and freeze-dried.
The freeze-dried glucosides were applied to a preparative
HPLC column (Gemini C18 10 30 mm diameter; Phenomenex) with an isocratic 20% acetonitrile gradient at a flow rate of
10 ml/min. Quercetin glucosides were identified by comparison
to known standards (3). The position of fisetin glucosylation was
confirmed by proton NMR (supplemental Table S2). HPLC UV
chromatogram (370 nm) peaks that did not correspond to a
known standard were confirmed as the monoglucosides of the
respective aglycone by electrospray ionization mass spectrometry
(data not shown). The assignment of glucosylation position to apigenin, kaempferol, and 3⬘4⬘7-trihydroxyflavone (THF) 4⬘-O-glucosides and THF 3⬘-O and 7-O-glucosides was based on comparison of HPLC spectra to known standards and by the comparison
of related flavonoid product elution profiles.
Regiospecific Glucosylation by Two A. thaliana GTs
15726 JOURNAL OF BIOLOGICAL CHEMISTRY
VOLUME 283 • NUMBER 23 • JUNE 6, 2008
FIGURE 1. Amino acid sequence alignment and secondary structure prediction of UGT74F1 and
UGT74F2. Sequence identity (76%) is shaded light gray, similarity (90%) dark gray. The diagnostic PSPG motif
of plant Family 1 GTs is underlined. The predicted secondary structure (analyzed using the JPred server) (45) of
UGT74F1 and UGT74F2 is identical and is illustrated by an arrow for a -sheet and a cylinder for an ␣-helix. Each
of the four amino acid positions (67, 112, 153, 239) corresponding to a domain-swapping shuffle point is
indicated by an asterisk.
Downloaded from http://www.jbc.org/ by guest on June 24, 2016
FIGURE 2. An HPLC-based assay to determine kinetic parameters of UGT74F1 and UGT74F2. A, the flavonoid quercetin (Q). B, recombinant UGT74F1 and UGT74F2 (2 g of each) analyzed by 10% (w/v) SDS-PAGE. C and
D, HPLC analysis of UGT74F1 and UGT74F2 activity toward 100 m quercetin. E and F, Hanes plot of UGT74F1 and
UGT74F2 activity toward the OH groups of quercetin. The error bars in E and F represent the S.D. of independent
triplicate data sets. The kinetic parameters kcat and Km for UGT74F1 and UGT74F2 activity are shown in Table 1.
(Fig. 2A) were determined. When
expressed in E. coli and assayed as
purified recombinant GST fusion
proteins (Fig. 2B), UGT74F1 forms
monoglucosides on the 7-, 3⬘-, and
4⬘-hydroxyls (Fig. 2C), whereas
UGT74F2 forms only the 7- and
4⬘-monoglucosides (Fig. 2D). Variation in amino acid sequence
between the enzymes is sufficient to
produce different product formation profiles. Thus, to identify crucial amino acids responsible for the
differing regiospecificity between
the two GTs, segments of sequence
were swapped between the two
open reading frames.
Kinetic Characterization of
UGT74F1 and UGT74F2 Activities
toward Quercetin—Conditions for
the enzyme reactions were established to meet the criteria for pseudo-single substrate kinetics. The
data for UGT74F1 and UGT74F2
were analyzed through the use of
Hanes plots (Fig. 2, E and F, respectively). The kinetic parameters for
the individual glucosides formed
were determined when first, quercetin acceptor concentration was
varied (Table 1) and second, UDPG
donor concentration was varied
(Table 2). The kcat and Km values
obtained by changing the acceptor
concentration explain the observed
difference in the UGT74F1 and
UGT74F2 product formation profile. It is clear that UGT74F1 and
UGT74F2 differ in both enzyme
turnover and Km. In terms of kcat,
UGT74F1 displays a higher turnover toward the 7-OH and 4⬘-OH of
quercetin than toward the 3⬘-OH;
by comparison, UGT74F2 shows
very low turnover toward the 7-OH
and 4⬘-OH positions, with no activity toward the 3⬘-OH (Table 1).
For both the GTs the Km for UDPG
was near identical, irrespective of
the acceptor hydroxyl glycosylated
(Table 2).
Construction and Thermal Denaturation Analysis of UGT74F1/
UGT74F2 Chimeras—As a step to
identifying the amino acid determinants of regioselective glycosylation
of quercetin within the sequences of
UGT74F1 and UGT74F2, a series of
Regiospecific Glucosylation by Two A. thaliana GTs
TABLE 1
The kinetic parameters kcat and Km and the specificity constant (kcat/Km) of UGT74F1, UGT74F2, and UGT74F1 N142Y toward quercetin, with a
fixed UDPG concentration
The parameters were determined for activity toward quercetin 7-OH, 4⬘-OH, and 3⬘-OH. Enzyme (0.2–2 g), quercetin concentration (4 –200 M), and reaction time
(0.5–10 min) were varied to analyze product using the pseudo-single substrate assumptions described under “Experimental Procedures.” UDPG concentration was
maintained in excess (7 mM). Data were analyzed by the use of Hanes plots, as shown in Fig. 2. n.d. indicates that product was observed but not in sufficient amounts to enable
determination of kinetic parameters. The data represent three independent replicates.
Quercetin
UGT74F1
UGT74F2
7-OH
Km (M)
kcat (s⫺1)
kcat/Km (M ⫺1 s⫺1)
10.6 ⫾ 0.6
0.99 ⫾ 8.4 ⫻ 10⫺2
93,297 ⫾ 3,230
55.2 ⫾ 4.8
0.04 ⫾ 8.8 ⫻ 10⫺3
1,030 ⫾ 172
15.5 ⫾ 3.1
0.07 ⫾ 4.1 ⫻ 10⫺3
4,519 ⫾ 1,100
4ⴕ-OH
Km (M)
kcat (s⫺1)
kcat/Km (M ⫺1 s⫺1)
23.8 ⫾ 1.3
0.85 ⫾ 8.9 ⫻ 10⫺2
35,545 ⫾ 3,935
72.8 ⫾ 10.2
0.04 ⫾ 3.2 ⫻ 10⫺4
353 ⫾ 91
7.4 ⫾ 1.9
2.1 ⫾ 3.2 ⫻ 10⫺1
279,914 ⫾ 59,032
3ⴕ-OH
Km (M)
kcat (s⫺1)
kcat/Km (M ⫺1 s⫺1)
17.7 ⫾ 3.9
0.15 ⫾ 9.8 ⫻ 10⫺2
8,317 ⫾ 7,846
The parameters were determined for activity toward quercetin 7-OH, 4⬘-OH, and
3⬘-OH. Enzyme (0.2–2 g), UDPG concentration (100 –3500 M), and reaction
time (0.5–10 min) were varied to analyze product using the pseudo-single substrate
assumptions described under “Experimental Procedures.” Quercetin concentration
was maintained in excess (200 M). The data represent three independent replicates. Data were analyzed by use of Hanes plots. F22221 data are discussed under
“Discussion.”
Quercetin
UGT74F1
UGT74F2
F22221
7-OH
Km (M)
kcat (s⫺1)
kcat/Km (M ⫺1 s⫺1)
1074 ⫾ 126
0.54 ⫾ 0.06
509 ⫾ 123
554 ⫾ 141
0.11 ⫾ 0.004
205 ⫾ 64
1328 ⫾ 188
0.026 ⫾ 0.002
19.6 ⫾ 1.2
4ⴕ-OH
Km (M)
kcat (s⫺1)
kcat/Km (M ⫺1 s⫺1)
1202 ⫾ 205
0.46 ⫾ 0.05
388 ⫾ 27
507 ⫾ 131
0.08 ⫾ 0.004
166 ⫾ 38
1100 ⫾ 435
0.020 ⫾ 0.002
19.4 ⫾ 6.3
3ⴕ-OH
Km (M)
kcat (s⫺1)
kcat/Km (M ⫺1 s⫺1)
1185 ⫾ 158
0.25 ⫾ 0.03
212 ⫾ 1
seven chimeras were constructed. This was achieved by chimeric PCR and through the introduction of three unique
restriction enzyme sites (see supplemental Fig. S2 for further
details). The modified parental open reading frames were designated UGT74F1* and UGT74F2* and contained four “shuffle
points” from which chimeras with sequence switched at amino
acid positions 67, 112, 153, and 239 were constructed (Fig. 3A).
These were purified as recombinant GST fusion proteins (Fig.
3B). Positions 67, 112, and 153 correspond to locations within
the predicted N-terminal Rossmann fold-like domain that has
been shown to be primarily responsible for acceptor interaction.
Position 239 corresponds to a location within the predicted linker
region connecting the two Rossmann fold-like domains.
Thermal denaturation profiles of recombinant protein without
the GST fusion tag were obtained for UGT74F1, UGT74F2, and
chimeras F22221 and F22211, which displayed the greatest modifications. As shown in Fig. 3C the four profiles were near superimposable, implying the thermal stability of the chimeras was not
altered.
Kinetic Characterization of UGT74F1*, UGT74F2*, and Chimeric Sequences—The kinetic parameters are provided in Fig. 4
in which kcat, Km, and kcat/Km are illustrated. The data confirm
JUNE 6, 2008 • VOLUME 283 • NUMBER 23
n.d.
that introduction of the shuffle points into UGT74F1 and
UGT74F2 sequences does not significantly alter the enzymic
kinetic characteristics; compare data described in Fig. 4 with
Table 1.
The chimeric enzymes display a range of alterations in kcat
and Km toward the hydroxyl groups of quercetin. Chimera
F22221, in which the entire N-terminal domain of UGT74F2* is
attached to the C-terminal domain of UGT74F1, displays
UGT74F2-like kcat and does not glucosylate the 3⬘-OH of quercetin. Similarly, chimera F22211 does not possess quercetin
3⬘-OH GT activity. However, this chimera shows a marked
increase in kcat at the 4⬘-OH compared with UGT74F2* and
F22221. Chimera F22111 does not possess an increased 4⬘-OH
kcat and also forms quercetin 3⬘-O-glucoside in addition to the
7-O- and 4⬘-O-glucosides. When chimera F11211 was analyzed
it was found that, compared with UGT74F1*, the kcat toward
the 7-OH was significantly reduced (10⫻) whereas the high kcat
toward the 4⬘-OH was retained. However, swapping the
remaining individual segments of UGT74F2* sequence into
UGT74F1* (F11121, F12111, and F21111) reduced, by varying degrees, the kcat toward all hydroxyl groups glycosylated
(Fig. 4A).
In terms of Km, a number of changes were observed in the
different chimeras (Fig. 4B). In particular, F11211 illustrates
that the Km in the glucosylation of the 4⬘-OH of quercetin can
be altered (decreased) while kcat remains unchanged, compared
with UGT74F1*. Also, for the same chimera to glucosylate the
7-OH of quercetin, the Km remains unchanged while kcat is
reduced significantly.
The kcat/Km values for UGT74F1*, UGT74F2*, and chimeric
enzymes provide a means for direct comparison of GT specificity for the flavonoid quercetin. Fig. 4C shows that the specificity
constant for the three hydroxyl groups of quercetin varies significantly between the different enzymes analyzed. The greatest
positive shift was observed in the glycosylation of the 4⬘-OH of
quercetin by chimera F11211. Thus, the domain-swapping
strategy identified a 40-amino acid region (residues 112–153 in
UGT74F1) capable of increased selectivity of catalysis toward
the 4⬘-OH of quercetin. Further interrogation of the amino
acids in this region of the protein enabled identification of the
specificity determinant.
JOURNAL OF BIOLOGICAL CHEMISTRY
15727
Downloaded from http://www.jbc.org/ by guest on June 24, 2016
TABLE 2
The kinetic parameters kcat and Km, and the specificity constant
(kcat/Km) of UGT74F1, UGT74F2, and F22221 toward UDPG, with a
fixed quercetin concentration
UGT74F1 N142Y
Regiospecific Glucosylation by Two A. thaliana GTs
Downloaded from http://www.jbc.org/ by guest on June 24, 2016
FIGURE 3. UGT74F1 and UGT74F2 chimeras. A, schematic representation of
parent UGT74F1*, UGT74F2*, and the generated chimeras. The introduced
shuffle points are given their equivalent amino acid position, partitioning the
primary sequence into five segments. Chimeras are named according to their
composition of UGT74F1 or UGT74F2 sequence. B, 10% (w/v) SDS-PAGE analysis of UGT74F1/F2 chimeric proteins (2 g of each). C, thermal denaturation
curves of UGT74F1(F), UGT74F2(⫹), F22221(Œ), and F22211(〫) recombinant
proteins with no GST fusion tag. The percentage change in CD signal at 220
nm, relative to 10 °C, was measured over the temperature range 10 to 80 °C.
Analysis of Individual Amino Acid Changes on the Specificity
of GT Activity toward Quercetin—Site-directed mutagenesis
was used to determine amino acid positions in segment 112–
153 that were critical for shifting specificity. In Fig. 5A, the
amino acid sequences of UGT74F1 and UGT74F2 within that
segment are shown, illustrating the ten amino acids that differ
between the two enzymes. When two of those amino acids in
UGT74F1, Ser-135 and Asn-142, were mutated to their
UGT74F2 equivalents, proline and tyrosine, respectively, the
combination mutant UGT74F1 S135P,N142Y possessed a
product formation profile similar to F11211. Analysis of the
15728 JOURNAL OF BIOLOGICAL CHEMISTRY
FIGURE 4. The kinetic parameters kcat, Km, and the specificity constant
(kcat/Km) of UGT74F1*, UGT74F2*, and chimeras toward quercetin.
Enzyme (0.2–2 g), quercetin concentration (4 –200 m), and reaction time
(0.5–10 min) were varied to analyze product using the pseudo-single substrate assumptions described under “Experimental Procedures.” UDPG concentration was maintained in excess (7 mM). Error bars represent S.D. of independent triplicate data sets.
single mutants showed that the N142Y mutation was sufficient
to amplify the observed shift in specificity toward the 4⬘-OH of
quercetin (Fig. 5B). Kinetic analysis of UGT74F1 N142Y
revealed that the primary kinetic cause of the altered product
formation profile was a reduction in turnover at the 7-OH position with a co-concomitant increase in turnover at the 4⬘-OH of
quercetin (Table 1). Further, although the Km of UGT74F1
N142Y toward the 7-OH position was not significantly altered
with respect to wild type, the Km was reduced 3-fold toward the
4⬘-OH of quercetin. Fig. 5B also shows that mutations at
UGT74F1 Asn-142 to a representative positively charged (Arg),
negatively charged (Asp), aliphatic (Leu), or hydrogen-bonding
VOLUME 283 • NUMBER 23 • JUNE 6, 2008
Regiospecific Glucosylation by Two A. thaliana GTs
(Ser) amino acid generated a quercetin product formation profile similar to that of F11211.
Activity toward Additional Flavonoid Substrates—Given that
the UGT74F1 N142Y mutant displayed a significantly altered
glucosylation profile of quercetin, a range of additional flavonoids were assayed as acceptors to gain further insights into
the interaction between substrate hydroxyls and enzyme. In
addition, mutants UGT74F1 N142A/D/R/L/S were assayed
against the same substrates to determine the potential role of
the amino acid side chain at UGT74F1 position 142. Data for
N142Y are illustrated in Fig. 6 for activities toward six additional flavonoids. Data for the remaining mutants are included
in supplemental Fig. S3.
Few general conclusions can be drawn from a comparison of
the glycosylation profiles of the different flavonoids by
UGT74F1 N142Y and the other Asn-142 mutants. However,
certain trends did emerge. For example, on all flavonoids
assayed, UGT74F1 N142Y showed a decreased level of 7-Oglucoside product. The increased production by UGT74F1
N142Y of a 4⬘-O-glucoside of quercetin was similarly observed
for the luteolin, kaempferol, and apigenin acceptors. For the
two flavonoids, fisetin and 3⬘4⬘7-trihydroxflavone, that do not
have a hydroxyl at the 5 position no increase in the level of
4⬘-O-glucoside was observed. No activity toward morin was
found for any enzyme assayed.
Production of Quercetin 4⬘-O-Glucoside—UGT74F1 N142Y
was assessed in a non-optimized E. coli shake flask fermentation for utility in preparative scale synthesis of quercetin 4⬘-Oglucoside. The GT culture converted quercetin to its 4⬘-O-glucoside at a linear rate for ⬃36 h (Fig. 7A). During the
fermentation, other glucosides represented ⬍5% of the total
JUNE 6, 2008 • VOLUME 283 • NUMBER 23
glucosylated product (data not shown), indicating that the in
vitro specificity of the enzyme is mirrored in vivo. Quercetin
and its glucosides were recovered from the culture medium by
concentration on an Amberlite XAD-2 column and then separated by HPLC to produce quercetin 4⬘-O-glucoside. The final
amount of purified product was 9.9 ⫾ 0.3 mg/liter culture, a
yield of ⬃17% (Fig. 7).
DISCUSSION
Plants contain a large multigene family of GTs capable of
conjugating a diverse range of small lipophilic molecules. These
enzymes are classified into Family 1 in the Carbohydrate Active
Enzyme (CAZy) data base (27). There is considerable potential
for using plant GTs as novel biocatalysts for regiospecific glycosylation and production of high value glycosides. However, in
order to realize the full potential of GTs in biocatalysis, it is
important to gain a thorough understanding of the kinetic
parameters that determine their activity. In this work, we have
established an HPLC-based methodology for determining
kinetic parameters of the multiple concurrent reactions of a GT
toward a single substrate. Using this approach we define the
kinetic basis for the differing regiospecificity of two A. thaliana
GTs, UGT74F1 and UGT74F2. Further, through a domainswapping approach we have identified an amino acid distal to
the active site that is important for determining the regiospecificity of UGT74F1. Taken together, these data inform both the
future design and the analysis of GT engineering experiments.
Several earlier studies have explored the regiospecificity of
GTs toward quercetin and other flavonoids (22, 23, 28). However, in each of these, although regiospecificity of products was
identified, only a single kinetic parameter was assigned and the
contribution of individual reactions could therefore not be disconnected. These studies have involved both individual GTs
from different plant species and mutant forms of a single GT. In
the latter, He and co-workers identified mutations in a MediJOURNAL OF BIOLOGICAL CHEMISTRY
15729
Downloaded from http://www.jbc.org/ by guest on June 24, 2016
FIGURE 5. Regiospecificity of UGT74F1 mutants toward quercetin.
A, amino acid alignment of UGT74F1 and UGT74F2 from position 112 to 153.
Amino acid identity is shown in light gray, similarity in dark gray. B, the sitedirected mutagenesis of UGT74F1 focused on Ser-135 and Asn-142. Error bars
represent the S.D. of independent triplicate data sets.
FIGURE 6. Regiospecificity of UGT74F1 and UGT74F1 N142Y toward a
range of flavonoid substrates. Error bars represent the S.D. of triplicate data
sets.
Regiospecific Glucosylation by Two A. thaliana GTs
cago truncatula GT, UGT71G1, that significantly shifted the
regiospecificity of glycosylation of quercetin (23). Whereas the
parental enzyme formed all five potential quercetin glucosides,
the F148V mutation was shown to focus activity to the formation of only quercetin 3-O-glucoside. By contrast, all of the
other active GT mutants formed at least four quercetin glucosides, each in varying proportion to the parent enzyme. The
kinetic approach used in this study would enable assignment
of the kinetic parameters kcat and Km to each of the glycosylating reactions performed, thereby providing additional
quantitative data for interpretation of observed alterations
in regiospecificity.
All Family 1 GTs are predicted to exhibit a GT-B fold comprised of two Rossmann fold-like domains. To date, crystallographic studies of GTs with a low comparative amino acid identity (⬃20 –30%) have shown strong structural conservation of
the core /␣/ Rossmann domains. There is also functional
conservation with respect to the interactions of N- and C-terminal domains with the acceptor or sugar donor. Typically,
amino acids interacting with the acceptor are located within the
N-terminal domain and those interacting with the sugar donor
are found in the C-terminal domain. The resulting prediction of
a discrete function to a specific domain makes domain swapping an enticing approach for the engineering of GTs.
Hoffmeister et al. (29) identified a variable region of amino acid
sequence between the urdamycin GTs UrdGT1b and UrdGT1c
15730 JOURNAL OF BIOLOGICAL CHEMISTRY
VOLUME 283 • NUMBER 23 • JUNE 6, 2008
Downloaded from http://www.jbc.org/ by guest on June 24, 2016
FIGURE 7. Whole-cell biotransformation of quercetin by E. coli expressing
UGT74F1 N142Y and purification of quercetin 4ⴕ-O-glucoside. A, time
course of quercetin 4⬘-O-glucoside (Q 4⬘-O-Glc) formation by 1 liter of shake
flask cultures of E. coli BL21 (DE3) harboring pGEX-2T/UGT74F1 N142Y. Time
point zero equates to quercetin (Q) addition. B, analysis of the amount of Q
4⬘-O-Glc during the initial concentration and purification of the fermentation
medium on an Amberlite XAD-2 column. The panel shows the total amount of
Q 4⬘-O-Glc in the filtrate (F) before application to the column, the flowthrough (FT), H2O wash (W), and the eluates of increasing acetonitrile concentration. Error bars represent the S.D. of triplicate data sets. C, preparative HPLC
spectra. Analysis of individual fractions identified quercetin 7,4⬘-di-O-glucoside (Q 7,4⬘-di-O-Glc), Q 4⬘-O-Glc, Q 3⬘-O-glucoside (Q 3⬘-O-Glc), and Q by comparison to known standards. D, HPLC analysis of purified Q 4⬘-O-Glc.
(91% identity) responsible for differentiating the activity of the
two enzymes. By domain swapping between two GTs of 85%
identity, Brazier-Hicks et al. (5) found a region of five variable
amino acids responsible for enabling the formation of N-glucosides in addition to O-glucosides. Other studies (30, 31)
found that at lower levels of sequence identity (75 and 28%,
respectively) the generated chimeras were inactive.
The data we present demonstrate the dual benefits of a
domain-swapping approach. First, the predicted transfer of a
property associated with a whole domain is illustrated clearly by
the chimera F22221. In this instance, the whole N-terminal
domain of UGT74F2 is fused to the C-terminal domain of
UGT74F1 and the chimera displays UGT74F2-like kinetic
parameters and regiospecificity toward the quercetin acceptor.
As anticipated, the F22221 chimera also displays UGT74F1-like
kinetic parameters toward the UDPG donor. Second, as exemplified by another chimera, F11211, an unexpected property
was revealed. In this instance, the regiospecificity of the chimera toward the 4⬘-OH of quercetin was significantly increased
relative to the UGT74F1 parent. It will be interesting to explore
the limits of GT structural modularity in the transfer of enzymic attributes. This would involve the discovery of enzymes
with novel activities such as through the recombination of
known activities for a designed outcome. Also, domain-swapping GTs of decreasing amino acid identity at either the Rossmann fold-like domain or structural element level could lead to
the discovery of additional unexpected activities.
Many enzyme recombination strategies target active site and
linking loops as a means of limiting disruption to the core secondary structure (32). The active site of GT-B fold enzymes is
principally comprised of loop regions (33) and is therefore an
intuitive starting point for mutagenesis. However, in UGT74F1
the amino acid mutation N142Y that was shown to be responsible for a drastic alteration in kcat/Km is predicted to lie within
helix N␣4. A superimposition of the four available plant GT
structures clearly showed that the amino acids corresponding
to Asn-142 occupy equivalent structural positions in helix N␣4
(UGT74F1 numbering), but no direct effects on active site residues or on substrate interaction could be directly deduced
from their structural position (supplemental Fig. S4). As others
have found, amino acid mutations without a direct substrate or
catalytic residue(s) interaction can have pronounced effects on
GT activity (5, 34). Only the crystallographic three-dimensional
structures of UGT74F1 and the N142Y mutant would reveal the
structural mechanism by which the regiospecificity of the
enzyme is altered.
A recent study, using a high-throughput screen to detect
novel donor and acceptor activities, revealed the surprising
ability of a Humicola insolens Cel7B glycosynthase mutant (35)
to glycosylate flavonoid scaffolds (36). Interestingly, the glycosynthase showed a ⬎95% regiospecificity toward the 4⬘-OH of
quercetin using the activated donor lactosyl fluoride. While glycosynthases have provided powerful tools for biocatalytic synthesis of carbohydrates (37), the study of the Cel7B mutant
enzyme demonstrated a potential wider utility. However, in
terms of preparative scale synthesis of the 4⬘-O-glucoside, the
GT mutant described in this study provides the added advantage of a whole-cell biocatalysis strategy. This strategy has been
Regiospecific Glucosylation by Two A. thaliana GTs
Acknowledgments—We thank Dr. Fabián E. Vaistij and Professor
Tony Wilkinson for helpful discussions.
REFERENCES
1. Bowles, D., Lim, E. K., Poppenberger, B., and Vaistij, F. E. (2006) Annu. Rev.
Plant Biol. 57, 567–597
2. Lim, E. K., and Bowles, D. J. (2004) EMBO J. 23, 2915–2922
3. Lim, E. K., Ashford, D. A., Hou, B. K., Jackson, R. G., and Bowles, D. J.
(2004) Biotechnol. Bioeng. 87, 623– 631
4. Lim, E. K., Doucet, C. J., Hou, B., Jackson, R. G., Abrams, S. R., and Bowles,
D. J. (2005) Tetrahedron Asymmetry 16, 143–147
5. Brazier-Hicks, M., Offen, W. A., Gershater, M. C., Revett, T. J., Lim, E. K.,
Bowles, D. J., Davies, G. J., and Edwards, R. (2007) Proc. Natl. Acad. Sci.
U. S. A. 104, 20238 –20241
6. Lim, E. K., Baldauf, S., Li, Y., Elias, L., Worrall, D., Spencer, S. P., Jackson,
R. G., Taguchi, G., Ross, J., and Bowles, D. J. (2003) Glycobiology 13,
139 –145
7. Hansen, K. S., Kristensen, C., Tattersall, D. B., Jones, P. R., Olsen, C. E.,
Bak, S., and Moller, B. L. (2003) Phytochemistry 64, 143–151
8. Hoffmeister, D., Wilkinson, B., Foster, G., Sidebottom, P. J., Ichinose, K.,
and Bechthold, A. (2002) Chem. Biol. 9, 287–295
9. Kubo, A., Arai, Y., Nagashima, S., and Yoshikawa, T. (2004) Arch. Biochem.
Biophys. 429, 198 –203
10. Kamra, P., Gokhale, R. S., and Mohanty, D. (2005) Nucleic Acids Res. 33,
W220 –W225
11. Thorsoe, K. S., Bak, S., Olsen, C. E., Imberty, A., Breton, C., and Moller,
B. L. (2005) Plant Physiol. 139, 664 – 673
12. Hollman, P. C. H., and Arts, I. C. W. (2000) J. Sci. Food Agric. 80,
1081–1093
13. Kramer, C. M., Prata, R. T. N., Willits, M. G., De Luca, V., Steffens, J. C.,
and Graser, G. (2003) Phytochemistry 64, 1069 –1076
14. Modolo, L. V., Blount, J. W., Achnine, L., Naoumkina, M. A., Wang, X. Q.,
and Dixon, R. A. (2007) Plant Mol. Biol. 64, 499 –518
15. Hall, D., and De Luca, V. (2007) Plant J. 49, 579 –591
JUNE 6, 2008 • VOLUME 283 • NUMBER 23
16. Hollman, P. C. H., vanTrijp, J. M. P., Buysman, M. N. C. P., VanderGaag,
M. S., Mengelers, M. J. B., deVries, J. H. M., and Katan, M. B. (1997) FEBS
Lett. 418, 152–156
17. van der Woude, H., Boersma, M. G., Vervoort, J., and Rietjens, I. M. C. M.
(2004) Chem. Res. Toxicol. 17, 1520 –1530
18. Erlund, I. (2004) Nutr. Res. 24, 851– 874
19. Cao, G. H., Sofic, E., and Prior, R. L. (1997) Free Radic. Biol. Med. 22,
749 –760
20. Day, A. J., Bao, Y. P., Morgan, M. R. A., and Williamson, G. (2000) Free
Radic. Biol. Med. 29, 1234 –1243
21. Day, A. J., Gee, J. M., Dupont, M. S., Johnson, I. T., and Williamson, G.
(2003) Biochem. Pharmacol. 65, 1199 –1206
22. Isayenkova, J., Wray, V., Nimtz, M., Strack, D., and Vogt, T. (2006) Phytochemistry 67, 1598 –1612
23. He, X. Z., Wang, X. Q., and Dixon, R. A. (2006) J. Biol. Chem. 281,
34441–34447
24. Hemsley, A., Arnheim, N., Toney, M. D., Cortopassi, G., and Galas, D. J.
(1989) Nucleic Acids Res. 17, 6545– 6551
25. Higuchi, R., Krummel, B., and Saiki, R. K. (1988) Nucleic Acids Res. 16,
7351–7367
26. Kelly, S. M., Jess, T. J., and Price, N. C. (2005) Bioch. Biophys. Acta 1751,
119 –139
27. Couthino, P. M., and Henrissat, B. (1999) in Recent Advances in Carbohydrate Bioengineering, pp. 3–12, The Royal Society of Chemistry,
Cambridge, UK
28. Vogt, T., Grimm, R., and Strack, D. (1999) Plant J. 19, 509 –519
29. Hoffmeister, D., Ichinose, K., and Bechthold, A. (2001) Chem. Biol. 8,
557–567
30. Kohara, A., Nakajima, C., Yoshida, S., and Muranaka, T. (2007) Phytochemistry 68, 478 – 486
31. Masada, S., Terasaka, K., and Mizukami, H. (2007) FEBS Lett. 581,
2605–2610
32. Carbone, M. N., and Arnold, F. H. (2007) Curr. Opin. Struct. Biol. 17,
454 – 459
33. Li, L. N., Modolo, L. V., Escamilia-Trevino, L. L., Achnine, L., Dixon, R. A.,
and Wang, X. Q. (2007) J. Mol. Biol. 370, 951–963
34. Williams, G. J., Zhang, C., and Thorson, J. S. (2007) Nat. Chem. Biol. 3,
657– 662
35. Ducros, V. M. A., Tarling, C. A., Zechel, D. L., Brzozowski, A. M., Frandsen, T. P., von Ossowski, I., Schulein, M., Withers, S. G., and Davies, G. J.
(2003) Chem. Biol. 10, 619 – 628
36. Yang, M., Davies, G. J., and Davis, B. G. (2007) Angew. Chem. Int. Ed. 46,
3885–3888
37. Hancock, S. M., Vaughan, D., and Withers, S. G. (2006) Curr. Opin. Chem.
Biol. 10, 509 –519
38. Weis, M., Lim, E. K., Bruce, N., and Bowles, D. (2006) Angew. Chem. Int.
Ed. 45, 3534 –3538
39. Lim, E. K., Ashford, D. A., and Bowles, D. J. (2006) ChemBioChem 7,
1181–1185
40. Oka, T., and Jigami, Y. (2006) FEBS J. 273, 2645–2657
41. Mendez, C., and Salas, J. A. (2001) Trends Biotechnol. 19, 449 – 456
42. Graefe, E. U., Wittig, J., Mueller, S., Riethling, A. K., Uehleke, B.,
Drewelow, B., Pforte, H., Jacobasch, G., Derendorf, H., and Veit, M. (2001)
J. Clin. Pharmacol. 41, 492– 499
43. Browning, A. M., Walle, U. K., and Walle, T. (2005) J. Pharm. Pharmacol.
57, 1037–1041
44. Murota, K., Mitsukuni, Y., Ichikawa, N., Tsushida, T., Miyamoto, S., and
Terao, J. (2004) J. Agric. Food Chem. 52, 1907–1912
45. Cuff, J. A., Clamp, M. E., Siddiqui, A. S., Finlay, M., and Barton, G. J. (1998)
Bioinformatics 14, 892– 893
JOURNAL OF BIOLOGICAL CHEMISTRY
15731
Downloaded from http://www.jbc.org/ by guest on June 24, 2016
successfully demonstrated for a diverse range of quercetin glycosides and those of other natural product scaffolds (3, 38).
Also, in the whole-cell system, a range of sugar donors can be
provided by engineered microbial hosts, bypassing the need to
supply exogenous cofactor required by in vitro reactions (39 –
41). When assessed in a non-optimized shake flask fermentation for utility in preparative scale synthesis, E. coli expressing
UGT74F1 N142Y converted quercetin aglycone to quercetin
4⬘-O-glucoside in substantial quantities. Significantly, conjugation of the 4⬘-position, compared with that of others, has been
shown to influence bioactivity of quercetin when assayed in
human metabolism studies (42) using in vivo models (20, 21, 43)
and in vitro assays (44).
In summary, we have assigned kinetic parameters to the multiple glycosylation reactions of a plant GT toward a single substrate. Further, a domain-swapping strategy has been used to
identify an amino acid position in UGT74F1 that is important
for determining specificity toward quercetin and other flavonoids. Application of the UGT74F1 N142Y mutant in an
E. coli whole-cell fermentation demonstrated the potential utility of this GT for the production of flavonoid 4⬘-O-glucoside.
SUPPLEMENTAL TABLE S1
Ologonucleotide primers used to create the chimeras and mutants described in this study
The UGT74F1 or UGT74F2 open reading frame template was cloned into the expression plasmid pGEX-2T. Nucleotides which differ from the
primer template sequence are in bold. Restriction enzyme sites within primers are underlined. The SpeI site was already present in UGT74F2.
Restriction enzyme sites were added sequentially to the ORF. A schematic representation of the 74F1* and 74F2* ORFs is provided in
Supplemental Fig. S2.
Primer ID
DNA
Template
Amino Acid
Mutation
UGT74F1
S151T
I
II
III
UGT74F2
V
VII
CCTTGACACTTCCCATCAAG
62.1
TACCATTGTTTATGTAAGAAAG
60.3
TACCTTGCAACTTCCCATTG
62.4
CCATTGTTTATGTAAGAAAGATAATAAAC
59.9
UGT74F1 or F2
-
Comments
Introduction of Kpn I restriction enzyme site, GGTACC
Introduction of Kpn I restriction enzyme site, GGTACC
CTAGTGATAACCCTATTACTTGTATCGTCTATG
63.7
TCTGGTGTTTGCGGATGATATC
65.8
ATCGATAGCCACCATCTCCGATG
69.9
ATAGGACTAGATGGGTCGAGGTGG
67.1
ATTGGTCCGGATAGGTCAGGATTG
70.2
TATTATCTTTCTTACATAAACAATGGTAGCTTGAC
65.3
For use with reverse primer XI
GATATAGTTAACGGCGCAAGACTGC
67.2
For creation of 74F1 N142 mutants
Introduction of Spe I restriction enzyme site, ACTAGT
S100T, T101S
VI
VIII
Tm (oC)
S151T
IV
UGT74F1
Oligonucleotide PrimerSequence 5'-3'
Introduction of Cla I restriction enzyme site, ATCGAT. Primer VII can be used with primer VIII or IX.
UGT74F1
IX
X
UGT74F1
N142Y
XI
XII
pGEX-2T
GTGATCATGTAACCCATCCTGACTTC
67.4
XIII
pGEX-2T
GTCAGTCAGTCACGATGAATTCAAA
61.1
ACGTTGGTCTAAGTAAATTGATGGAAC
64.8
XIV
UGT74F2
For F22221 generation. Primer XII to partner XIV in PCR 1 of the overlap extension PCR (OE-PCR). For
F22221 generation. Primer XIII to partner XV in PCR 2 of the OE-PCR. PCR reaction 3 of the OE-PCR uses
the product of PCR reactions 1 and 2 with primers XII and XIII. Primer XIII contains an Eco RI site that
corresponds to the 3' segment of the vector multiple cloning site.
XV
UGT74F1
TACTTAGACCAACGTATCAAATCAGACAACGAC
70.1
XVI
UGT74F1
N142A
GCTTATCTTTCTTACATAAACAATGGTAGCTTG
66.6
For use with reverse primer IX
XVII
UGT74F1
N142D
GATTATCTTTCTTACATAAACAATGGTAGCTTG
65.0
For use with reverse primer IX
XVIII
UGT74F1
N142L
CTGTATCTTTCTTACATAAACAATGGTAGCTTG
66.0
For use with reverse primer IX
XIX
UGT74F1
N142R
CGTTATCTTTCTTACATAAACAATGGTAGCTTG
67.0
For use with reverse primer IX
XX
UGT74F1
N142S
AGCTATCTTTCTTACATAAACAATGGTAGCTTG
66.0
For use with reverse primer IX
SUPPLEMENTAL TABLE S2 1H-NMR (700 MHz, DMSO-d6) spectral data of fisetin
and its 4’- and 7-O-glucosides. Chemical shifts are given on a parts-per-million (ppm)
scale with TMS as internal standard (d, doublet; dd, doublet of doublet; m, multiplet; J,
coupling constant). The multiplet observed from fisetin 7-O-glucoside at 6.98-6.99 ppm is
due to overlapping data.
Position
Fisetin
C5
7.94 (1H, d, J = 9.4 Hz)
7.94 (1H, d, J = 8.75 Hz)
7.93 (1H, d, J = 8.75 Hz)
C6
7.56 (1H, dd, J = 8.4, 1.68 Hz)
7.64 (1H, dd, J = 8.61, 1.82 Hz)
7.86 (1H, dd, J = 8.51, 1.86 Hz)
C8
7.70 (1H, d, J = 1.82 Hz)
7.73 (1H, d, J = 1.82 Hz)
7.79 (1H, d, J = 1.75 Hz)
C2'
4'-O-glucoside
7-O-glucoside
6.95 (1H, d, J = 1.68 Hz)
6.98-6.99 (2H, m)
C5'
C6'
6.92 - 6.89 (3H, m)
7.26 (1H, d, J = 8.68 Hz)
6.92 (1H, dd, J = 8.79, 1.79 Hz)
6.92 (1H, dd, J = 8.75, 2.03 Hz)
Supplementa1 Figure S1
KDa
UGT
74F1
GSTUGT
74F1
70
50
20
SUPPLEMENTAL FIGURE S1 SDS-PAGE analysis of UGT74F1. Lane 1, molecular
weight marker; Lane 2, UGT 74F1 (2 g) prepared by thrombin mediated cleavage of
glutathione sepharose 4B bound GST-UGT74F1; Lane 3, GST-UGT74F1 (2 g)
prepared in parallel to the sample in Lane 2 but eluted from glutathione sepharose 4B by
glutathione elution buffer (100 mM Tris-Cl pH 8.0, 20 mM reduced glutathione, 120 mM
NaCl).
Supplementa1 Figure S2
A
74F1
Restriction enzyme
site
B
1
67
112
153
239
449
BamHI
ClaI
SpeI
KpnI
EcoRI
-
-
S100T
T101S
S151T
-
74F2
Restriction enzyme
site
1
67
112
153
239
449
BamHI
ClaI
SpeI
KpnI
EcoRI
-
-
-
S151T
-
SUPPLEMENTAL FIGURE S2 Site-directed mutagenesis for domain swapping.
Additional restriction sites were introduced into UGT74F1 and UGT74F2 (underlined) by
site-directed mutagenesis for the subsequent domain swapping experiments. Whilst
introduction of a ClaI site in both UGT74F1 and UGT74F2 results in a silent mutation,
creation of the SpeI site in UGT74F1 and KpnI site in both sequences lead to amino acid
mutations that are shown in the figure. BamHI and EcoRI sites were created during
cloning of the open reading frame, with BamHI located upstream of the start codon and
EcoRI after the stop codon. The switch point at position 239 is indicated for reference.
This is the amino acid location equivalent to site the nucleotide switch point used in
overlap extension PCR. The sequence of all oligonucleotides used in this study are found
in Supplemental Table S1.
30
Supplementa1 Figure S3
A
B
UGT74F1 N142A
40
50
40
35
30
25
20
35
30
nkat/mg
7-OH
4’-OH
3’-OH
* 3-or 5-OH
3-or 5-OH
45
nkat/mg
UGT74F1 N142L
25
20
15
15
10
10
5
5
*
0
Q
C
L
F
THF
K
A
M
Q
D
UGT74F1 N142S
F
THF
K
A
M
A
M
UGT74F1 N142D
10
nkat/mg
20
nkat/mg
L
12
25
15
10
*
8
6
4
5
2
*
0
0
Q
E
*
0
L
F
THF
K
A
M
Q
L
F
THF
K
UGT74F1 N142R
3.0
nkat/mg
2.5
2.0
1.5
1.0
*
0.5
0.0
Q
L
F
THF
K
A
M
SUPPLEMENTAL FIGURE S3 Regiospecificity of UGT74F1 N142 mutants towards
a range of flavonoid substrates. Q, quercetin; L, luteolin; F, fisetin; THF, 3’4’7
trihydroxyflavone; K, kaempferol; A, apigenin; M, morin.
Supplementa1 Figure S4
SUPPLEMENTAL FIGURE S4. Structural alignment of plant GTs highlighting the
region Nα4 and the residues equivalent to UGT74F1 Asn142. Structures shown are
Vitis vinifera vvGT1 (green, PDB ID: 2c1z), Medicago truncatula UGT71G1 (blue,
PDB ID: 2acv), Medicago truncatula UGT85H2 (gold, PDB ID: 2pq6) and Arabidopsis
thaliana UGT72B1 (red, PDB ID: 2vch). A, vvGT1 with the ligands kaempferol and
UDP-2-fluoro-glucose. Superimposed is the structurally aligned Nα4 (with linking
loops. UGT74F1 numbering, see Fig. 1) of UGT71G1, UGT85H2 and UGT72B1.
Based on sequence and secondary structure alignment the residue equivalent to
UGT74F1 Asn142 in each of the structures was identified, and the side chain is
indicated by an arrow. B, magnified view of the structurally aligned Nα4. C, residues
of the four GTs of analysed structure that are potentially equivalent to UGT74F1
Asn142.
A Kinetic Analysis of Regiospecific Glucosylation by Two Glycosyltransferases of
Arabidopsis thaliana: DOMAIN SWAPPING TO INTRODUCE NEW
ACTIVITIES
Adam M. Cartwright, Eng-Kiat Lim, Colin Kleanthous and Dianna J. Bowles
J. Biol. Chem. 2008, 283:15724-15731.
doi: 10.1074/jbc.M801983200 originally published online March 31, 2008
Access the most updated version of this article at doi: 10.1074/jbc.M801983200
Alerts:
• When this article is cited
• When a correction for this article is posted
Supplemental material:
http://www.jbc.org/content/suppl/2008/04/02/M801983200.DC1.html
This article cites 44 references, 9 of which can be accessed free at
http://www.jbc.org/content/283/23/15724.full.html#ref-list-1
Downloaded from http://www.jbc.org/ by guest on June 24, 2016
Click here to choose from all of JBC's e-mail alerts