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Gene Cloning and Prokaryotic Expression of Glycosyltransferase from Leonurus heterophyllus Sweet(英文稿)

益母草糖基转移酶基因的克隆及原核表达分析(英文稿)



全 文 :植物科学学报  2016ꎬ 34(3): 397~405
Plant Science Journal http: / / www.plantscience.cn
DOI:10􀆰 11913 / PSJ􀆰 2095-0837􀆰 2016􀆰 70001
徐德宏ꎬ 谭朝阳. 益母草糖基转移酶基因的克隆及原核表达分析[J] . 植物科学学报ꎬ 2016ꎬDOI:10􀆰 11913 / PSJ􀆰 2095-0837􀆰 2016􀆰 70001
XU DHꎬ TAN CY. Gene cloning and prokaryotic expression of glycosyltransferase from Leonurus heterophyllus Sweet[J] . Plant Science
Journalꎬ2016ꎬDOI:10􀆰 11913 / PSJ􀆰 2095-0837􀆰 2016􀆰 70001
益母草糖基转移酶基因的克隆及原核表达分析
徐德宏ꎬ 谭朝阳∗
(湖南中医药大学药学院生物工程实验室ꎬ 长沙 410208)
摘  要: 通过 cDNA 末端快速扩增技术 ( rapid amplification of cDNA endsꎬ RACE)从益母草 ( Leonurus
heterophyllus Sweet)叶片中克隆获得了一个编码糖基转移酶的基因(LhsUGT)ꎮ 该基因 cDNA全长为 1562 bpꎬ
开放阅读框(open reading frameꎬ ORF)为 1368 bpꎬ 编码 455 个氨基酸残基ꎬ 其分子量和等电点分别为
50􀆰 47 kD 和 5􀆰 52ꎮ 生物信息学分析结果显示: LhsUGT 编码的酶蛋白含有 3 种二级结构ꎬ 其中 α 螺旋占
43􀆰 1%ꎬ β折叠片占 17􀆰 5%ꎬ 无规卷曲占 39􀆰 4%ꎬ 其 C 端还发现了一段高度保守的 PSPG 结构域ꎬ 说明
LhsUGT 编码的酶蛋白属于植物糖基转移酶超家族ꎻ 对 LhsUGT的氨基酸序列进行 BLAST 同源比对ꎬ 发现益母
草与其它植物的糖基转移酶序列相似性为 26􀆰 4%~68􀆰 0%ꎻ 系统进化树分析表明ꎬ LhsUGT 蛋白属于拟南芥糖
基转移酶超家族的 L组ꎬ 故推测它可能具有催化简单酚类发生糖基化的功能ꎻ SDS ̄PAGE 电泳显示ꎬ 原核表达
系统成功表达出分子量约为 69 kD的 LhsUGT重组蛋白ꎬ 其 N端含有一段 17􀆰 9 kD的 His标签ꎬ 且在 IPTG诱导
5 h后达到最高表达量ꎮ 本研究结果为进一步开展体外酶促反应、 阐明益母草糖基转移酶的生物学功能奠定了
基础ꎮ
关键词: 益母草ꎻ 糖基转移酶基因ꎻ cDNA克隆ꎻ 生物信息学分析ꎻ 原核表达
中图分类号: Q943          文献标识码: A          文章编号: 2095 ̄0837(2016)03 ̄0397 ̄09
      收稿日期: 2015 ̄10 ̄10ꎬ 退修日期: 2015 ̄11 ̄12ꎮ
  基金项目: 湖南省“中药学”重点学科建设项目资助(湘教通[2011]76 号)ꎻ 湖南省教育厅资助科研项目(13C670)ꎻ 湖南中医药大学
青年科研基金项目(99820001 ̄93)ꎮ
This work was supported by grants from the Construct Program of the Key Discipline of Chinese Pharmacy in Hunan Province
([2011]76)ꎬ Scientific Research Fund of Hunan Provincial Education Department(13C670)ꎬ and the Youth Research Fund of Hu ̄
nan University of Chinese Medicine (99820001 ̄93) .
  作者简介: 徐德宏(1986-)ꎬ 男ꎬ 硕士ꎬ 讲师ꎬ 研究方向为中药生物技术(E ̄mail: xudehong163@126􀆰 com)ꎮ
  ∗通讯作者(Author for correspondence􀆰 E ̄mail: tomtzy@163􀆰 com)ꎮ
Gene Cloning and Prokaryotic Expression of Glycosyltransferase
from Leonurus heterophyllus Sweet
XU De ̄Hongꎬ TAN Chao ̄Yang∗
(Laboratory of Biological Engineeringꎬ College of Pharmacyꎬ Hunan University of Chinese Medicineꎬ Changsha 410208ꎬ China)
Abstract: A glycosyltransferase gene ( LhsUGT) was cloned from Leonurus heterophyllus
Sweet using rapid amplification of cDNA ends (RACE) . The full length cDNA of LhsUGT was
1562 bpꎬ with a 1368 bp open reading frame (ORF) encoding a 455 amino ̄acid protein
(LhsUGT) and a molecular weight of 50􀆰47 kD and isoelectric point of 5􀆰52. By bioinformatics
analysisꎬ three secondary structures were discovered in LhsUGTꎬ including 43􀆰1% helixꎬ
17􀆰5% β ̄sheet and 39􀆰4% random coil structural elements. There was a conserved PSPG
domain at the C ̄terminal of LhsUGTꎬ demonstrating that the enzyme encoded by LhsUGT
belonged to the glucosyltransferase super family. Homology analysis by BLAST showed that
the sequence similarities of glycosyltransferase between L. heterophyllus and other plants were
26􀆰4% - 68􀆰0%. Phylogenetic tree analysis indicated that LhsUGT might glycosylate simple
phenolic compounds as it was found to be clustered with group L in Arabidopsis thaliana.
SDS ̄PAGE analysis showed recombinant LhsUGT with approximate molecular weight of 69 kD
was successfully expressed by a prokaryotic expression systemꎬ which contained His tags of
17􀆰9 kD at the N ̄terminal and reached maximum expression level until 5 h after induction by
IPTG (Isopropyl β ̄D ̄1 ̄thiogalactopyranoside). The results in the study will lay the foundation for
future studies on the biological functions of LhsUGT by enzymatic reactions in vitro.
Key words: Leonurus heterophyllus Sweetꎻ Glycosyltransferaseꎻ cDNA cloningꎻ Bioinformatics
analysisꎻ Prokaryotic expression
    Plant cells have the ability to produce diffe ̄
rent kinds of natural products through secondary
metabolism. These natural products ( called se ̄
condary metabolites) need to be modified during
the production processꎬ which includes methyla ̄
tionꎬ hydroxylationꎬ and acylation[1ꎬ 2] . Glycosyla ̄
tion can significantly influence the stabilityꎬ
solubility and bioactivity of secondary metabolites
in plant cells[3ꎬ 4] . Furthermoreꎬ glycosylation is
catalyzed by a family of glycosyltransferases
(GTs)ꎬ which can transfer sugars from nucleo ̄
tide sugars (usually UDP ̄glucoseꎬ UDPG) to di ̄
fferent acceptorsꎬ such as phenolic compoundsꎬ
terpenoidsꎬ flavonoidsꎬ and alkaloidsꎬ resulting
in these acceptors forming different glycosylated
secondary metabolites[5-8] .
Leonurus heterophyllus Sweet belongs to
Labiatae in the plant kingdom and is an annual or
biennial herb with important efficacy in traditional
Chinese medicine treatmentꎬ such as activating
blood to regulate menstruationꎬ removing heat
and toxic materialꎬ and encouraging diuresis de ̄
tumescence. Modern research has indicated that
among all chemical compositions derived from L.
heterophyllusꎬ some secondary metabolitesꎬ
including alkaloidsꎬ flavonoidsꎬ and diterpe ̄
noidsꎬ exhibit pharmacological effects[9] . Our
preliminary study found that if some precursors
were added to nutrient solution for L. heterophyl ̄
lus cultureꎬ important secondary metabolites
could be synthesized. For exampleꎬ L. hetero ̄
phyllus could synthesize salidroside in nutrient
solution containing tyrosol[10] . As certain research
has reported that salidroside is the product of
tyrosol after glycosylation[11-13]ꎬ glycosyltransfe ̄
rase may exist in L. heterophyllus in order to
glycosylate tyrosol into salidroside.
Hereꎬ we isolated a gene coding glyco ̄
syltransferase from L. heterophyllus ( named
LhsUGT) by rapid amplification of cDNA ends
(RACE)ꎬ and then determined the nucleotide se ̄
quence and analyzed it using bioinformatics. We
also constructed a prokaryotic expression system
of glycosyltransferase and assayed the expres ̄
sion of recombinant protein with SDS ̄PAGE and
Western blot. This study will help lay a theoretical
foundation for using L. heterophyllus glycosyltra ̄
nsferase to biosynthesize certain valuable natural
products in the future.
1  Materials and Methods
1􀆰 1  Materials
The L. heterophyllus samples was cultured
by the Laboratory of Biological Engineeringꎬ
College of Pharmacyꎬ Hunan University of Chinese
Medicineꎬ using nutrient solution. The pMD19 ̄T
vector (Takara)ꎬ LA Taq (Takara)ꎬ DNA ladder
markers (Takara)ꎬ Trizol reagent ( Invitrogen)ꎬ
QIAquick® gel extraction kit (Qiagen)ꎬ SMARTTM
race cDNA amplification kit (Clonthech)ꎬ restric ̄
tion enzyme (Thermo Fisher Scientific)ꎬ anti ̄His ̄
Tag rabbit polyclonal antibody (EarthOx)ꎬ goat
anti ̄rabbit IgG ̄HRP (Abmart)ꎬ DAB horseradish
peroxidase color development kit ( Beyotime)ꎬ
and pET ̄32a express vector ( Novagen) were
purchased from different companies. All other
893 植 物 科 学 学 报 第 34卷 
chemicals and reagents were of analytical grade.
1􀆰 2  Molecular cloning of LhsUGT cDNA
Molecular cloning manipulations were pe ̄
rformed according to the protocol described by
Zhao et al.[14] and the SMARTTM race cDNA
amplification kit user manual. Firstꎬ total RNA was
extracted from L. heterophyllus leaves using the
Trizol reagentꎬ and was then converted into
cDNA using SMARTScribeTM reverse transcriptase
with a universal oligo ( dT) containing adapter
primer (Table 1) . Secondꎬ a pair of degenerate
primers ( LhsUGT ̄F and LhsUGT ̄Rꎬ Table 1 )
were designed corresponding to the conserved
domains of glycosyltransferase from related spe ̄
cies. The cDNA was amplified by PCR using the
degenerate primers and according to the pro ̄
gram: initial denaturation (94℃ for 3 min)ꎬ 30
cycles including denaturation ( 94℃ for 30 s)ꎬ
annealing (55℃ for 30 s)ꎬ elongation (72℃ for
1 min)ꎬ and final elongation (72℃ for 10 min) .
Finallyꎬ based on the partial cDNA sequence of
LhsUGT determined by PCRꎬ the 3′RACE gene
specific primers (3′GSP1 and 3′GSP2ꎬ Table 1)
and 5′RACE gene specific primers (5′GSP1 and
5′GSP2ꎬ Table 1) were designed. Both 3′RACE
and 5′RACE PCR were carried out as per the kit
user manual. All PCR products were gel ̄purified
using the QIAquick® gel extraction kitꎬ ligated
into the pMD19 ̄T vector and sequenced by a se ̄
quencing company. The 3′RACE and 5′RACE se ̄
quencing results were overlapped to splice a full ̄
length cDNA of LhsUGT.
1􀆰 3  Bioinformatics analysis of LhsUGT
We used ORF Finder (http: / / www.ncbi.nlm.
nih.gov / projects / gorf / ) to determine the open
reading frame (ORF) of the full ̄length cDNA of
LhsUGT. Based on the ORF of LhsUGTꎬ the
amino acid sequence of LhsUGT was deduced
by DNAman software. The online protein analysis
database ExPASy (http: / / www.expasy.org / )
was used to analyze molecular weight (MW)ꎬ
isoelectric point (pI) and highly conserved motif
sequences of LhsUGT. To investigate the amino ̄
acid sequence similarities of LhsUGT with other
UGTs from different plantsꎬ a BLASTP search
(http: / / blast.ncbi.nlm.nih.gov / Blast.cgi) was
conducted using the NCBI database. Using
Mega 3􀆰1 software to align LhsUGT with the A.
thaliana UGT superfamilyꎬ a phylogenetic tree
was constructedꎬ which could roughly predict the
substrate type of LhsUGT. We used MITOPROT
(http: / / ihg.gsf.de / ihg / mitoprot.html) and Target
P ( http: / / www. bs. dtu. dk / services / TargetP / )
to describe localization of LhsUGT in cells. To
predict secondary and tertiary structures of
LhsUGTꎬ the deduced amino acid sequence was
submitted to two databases: PORTER ( http: / /
distill.ucd.ie / porter / ) and SWISS ̄MODEL (http: / /
swissmodel.expasy.org / ) .
1􀆰 4  Prokaryotic expression and characterization
of recombinant LhsUGT
To obtain the ORF fragment of LhsUGTꎬ
cDNA from total RNA of L. heterophyllus leaves
was amplified with a pair of expressive primers
Table 1  Primer sequences
Primer name Primer sequence (5′ - 3′)
Adapter primer AAGCAGTGGTATCAACGCAGAGTAC(T) 30N-1N
LhsUGT ̄F TTCCAGCNCAAGGCCAYATHAAT
LhsUGT ̄R TCRAATGCATCAAAYGTRTTCAC
3′GSP1 ATGTCACCTTCGCCACCAGCGTTTA
3′GSP2 CTACCACTATTTCCACGGCTACGG
5′GSP1 CGCGTTTGGCGAGGGTTGTAATT
5′GSP2 GGCGGGTTGAATCCAGAG
LhsUGT ̄expression ̄F CATGCCATGGCTGACGACGACGACAAGATGGAGAGGCGCCACGTGCTCCTGG
LhsUGT ̄expression ̄R CCGCTCGAGTTAATTGAAAAACGCCTTCAAATTC
    Notes: The underline indicates the restriction sites.
993  第 3期                      徐德宏等: 益母草糖基转移酶基因的克隆及原核表达分析(英文)
(LhsUGT ̄expression ̄F and LhsUGT ̄expression ̄
Rꎬ Table 1)ꎬ which respectively contained a NcoⅠ
site and XhoⅠsite at the 5′ end. The PCR product
was ligated into the pET ̄32a express vector
digested with NcoⅠand XhoⅠ. The recombinant
construct was expressed as a fusion proteinꎬ with
big tags including a Trx􀅰Tagꎬ a 6 × His ̄Tagꎬ an
S􀅰Tagꎬ a thrombin cleavage site and two ente ̄
rokinase sites. The ligated vector was then tra ̄
nsformed into E. coli strain BL21 ( DE3 ) and
plated on LB plates containing 100 μg / mL
ampicillin. Single colonies carrying LhsUGT / pET ̄
32a were inoculated into LB liquid medium
(100 μg / mL ampicillin) and grown overnight at
37℃. The culture was diluted 1 ∶ 100 into 50 mL
LB broth and incubated at 37℃ until the OD600
was 0􀆰6. Recombinant expression was induced
by the addition of IPTG ( Isopropyl β ̄D ̄1 ̄
thiogalactopyra ̄noside) to a final concentration of
0􀆰5 mmol / L and incubated for 5 h at 27℃. Before
induction and 1ꎬ 2ꎬ 3ꎬ 4ꎬ and 5 h after inductionꎬ
the cells were harvested according to the same
biomass by centrifugation at 5000 r / min for
20 min. After centrifugationꎬ the supernatant was
aspiratedꎬ while the precipitate was resuspended
in a loading sample buffer (100 mmol / L Tris ̄
HClꎬ pH 6.8ꎬ 20% glycerolꎬ 4% SDSꎬ 200 mmol / L
DTTꎬ a trace of bromophenol blue) and boiled
for 5 min. SDS ̄PAGE was performed according
to Laemmli[15] under denaturing conditions on a
12% polyacrylamide slab gel to analyze the
recombinant LhsUGT weight distribution. The
resolved proteins in the gel were fixed with 10%
acetic acid / 40% methanol and visualized by stai ̄
ning with Coomassie brilliant blue G ̄250. For veri ̄
fying the correct expression of the recombinant
LhsUGTꎬ Western blot analysis was carried out.
After SDS ̄PAGEꎬ proteins in gel were transferred
into nitrocellulose filters. The membranes were
then blocked by skim milk and incubated in
primary anti ̄His ̄Tag rabbit polyclonal antibody
(1 ∶ 20000 dilution) . After washingꎬ horseradish
peroxidase conjugated anti ̄rabbit goat IgG (1 ∶
3000 dilution) was used as a secondary antibody
and the reaction was developed with DAB as the
substrate.
2  Results and Analysis
2􀆰 1  Cloning of LhsUGT
A 585 bp cDNA fragment of LhsUGT was
amplified by a pair of degenerate primersꎬ
LhsUGT ̄F and LhsUGT ̄R (Fig􀆰 1: A) . Based on
this cDNA fragmentꎬ 3′RACE and 5′RACE gene
specific primers were designed to obtain a
1086 bp 3′ cDNA end and a 512 bp 5′ cDNA
end using nested PCR ( Fig􀆰 1: B and C) . By
overlapping the 3′ cDNA and 5′ cDNA endsꎬ
a 1562 bp full ̄length cDNA of LhsUGT was
assembled. It had three distinct parts: a 5′ ̄
untranslated region (UTR)ꎬ an ORF and a 3′ ̄
UTR (Fig. 2) . The 5′ ̄UTR was 59 bp long and
the ORF was 1368 bp long (Fig􀆰 1: D) . The 3′ ̄
4M M M M1 2 3
100
500
600
800
400
300
200
A
2000
1200
1000
800
600
400
200
B
800
1000
600
400
200
C
2000
1400
1000
800
600
400
200
D
bp bp bp bp
A: M is a 100 bp markerꎬ lane 1 is the PCR product of the LhsUGT cDNA fragment. B: M is a 200 bp markerꎬ lane 2 is the PCR
product of the LhsUGT 3′RACE end. C: M is a 200 bp markerꎬ lane 3 is the PCR product of the LhsUGT 5′RACE end. D: M is a
200 bp markerꎬ lane 4 is the PCR product of the ORF of LhsUGT. Agarose gel: 1%ꎻ Voltage: 120 mVꎻ Time: 30 min.
Fig. 1  Electrophoresis of LhsUGT PCR products
004 植 物 科 学 学 报 第 34卷 
UTR was 135 bp long and contained a 12 bp poly
(A) tail (Fig. 2) . The full ̄length cDNA sequence
of LhsUGT was submitted to GenBank and as ̄
signed the accession number KP025966.
2􀆰 2  Sequence analysis of LhsUGT
The ORF of LhsUGT encoded a 455 amino ̄
acid polypeptide with an average molecular
weight of 50􀆰47 kD and theoretical pI of 5􀆰52. The
amino ̄acid sequence similarities of LhsUGT with
other plant UGTs from Sesamum indicum (XP_
011101592􀆰1)ꎬ Lycium barbarum (BAG80544􀆰1)ꎬ
Medicago truncatula ( XP003601706􀆰1)ꎬ Oryza
sativa Japonica Group ( BAD34401)ꎬ Rhodiola
sachalinensis (ABP49574􀆰1) and Gossypium hi ̄
rsutum (ABN58740) were 68%ꎬ 66%ꎬ 53􀆰8%ꎬ
41􀆰4%ꎬ 36􀆰6%ꎬ and 26􀆰4%ꎬ respectively (Fig􀆰 3).
Using MITOPROT and Target P to analyze the
localization of LhsUGT in cells showed that
LhsUGT was probably a mitochondrial protein
with a leader peptide at the N ̄terminal (Fig. 2) .
A phylogenetic tree was constructed according to
the UGTs from L. heterophyllus and A. thaliana
(Fig. 4) . Secondary structure prediction showed
that LhsUGT contained α ̄helix ( 43􀆰1%)ꎬ β ̄
extended (17􀆰5%) and coil (39􀆰4%) structural
elements. With homology modelingꎬ a tertiary
structure of LhsUGT was constructed (Fig. 5) .
2􀆰 3  Expression of recombinant LhsUGT
Recombinant LhsUGT was expressed by
E. coli strain BL21 (DE3) and analyzed by SDS ̄
PAGE and Western blot. Results showed a band
of approximately 69 kD on SDS ̄PAGEꎬ similar
to the calculated molecular mass of 68􀆰4 kDꎬ
including tags of 17􀆰9 kD (Fig. 6: A) . The time
gradient was used to assay the optimum expres ̄
sive time after induction by IPTG. The results indi ̄
cated that with the extension of timeꎬ the expres ̄
sive amount of recombinant LhsUGT gradually
increased until 5 h after induction when it reached
maximum expression ( Fig. 6: A) . Western blot
analysis of samples confirmed the correct expres ̄
sion of LhsUGT in E. coli (Fig. 6: B) .
3  Discussion
Glycosyltransferases are a class of important
enzymes that function to glycosylate secondary
metabolites in plants. In this studyꎬ a UGT from
L. heterophyllus was cloned and characterized.
The results showed that LhsUGT had a highly
conserved plant secondary product GTase do ̄
main ( named PSPG domainꎬ Fig. 2 ) [8ꎬ 16ꎬ17]ꎬ
which was similar to UGTs from S. indicum and L.
barbarum and belonged to group L of the A.
thaliana family 1 UGTs according to phylogenetic
analysis.
The PSPG domain is related to substrate
recognition and catalytic activity of GTs and
contains 44 amino acidsꎬ with the 22ndꎬ 23rdꎬ and
44th amino acids playing important roles in the
choice of sugar donors[18] . Trp22 in PSPG is
responsible for recognizing UDP ̄glucoseꎬ while
Arg22 utilizes UDP ̄glucuronic acid as a sugar
donor[19-21] . Ser23 in PSPG of UDP ̄glucurono ̄
syltransferases is highly conserved. The His44 in
PSPG exhibits activity with UDP ̄galactose as a
sugar donorꎬ whereas Gln44 in PSPG exhibits
glucosyltransferase[22] . The 22ndꎬ 23rdꎬ and 44th
amino acids in the PSPG of LhsUGT are Trpꎬ Asn
and Glnꎬ so we might speculate that LhsUGT is a
glucosyltransferase using UDP ̄glucose as a
sugar donor.
The A. thaliana genome has been se ̄
quenced and annotatedꎬ with more than 100
genes predicted to express family 1 UGTs. Com ̄
prehensive phylogenetic analysis of the A. thalia ̄
na family 1 UGT sequences determined they were
grouped into 14 phylogenetic clusters (group A-
N)ꎬ which evolved from 14 different functional
ancestral genes[8ꎬ 16ꎬ17] . The phylogeny of the A.
thaliana family 1 UGTs suggests that if UGTs from
other plant species were integrated into the Ara ̄
bidopsis phylogenetic treeꎬ their functions could
be preliminarily predicted[8ꎬ 16ꎬ17ꎬ 23] . Thusꎬ we
executed the above strategy and a comprehensive
104  第 3期                      徐德宏等: 益母草糖基转移酶基因的克隆及原核表达分析(英文)
204 植 物 科 学 学 报 第 34卷 
304  第 3期                      徐德宏等: 益母草糖基转移酶基因的克隆及原核表达分析(英文)
UGT84A2
L
G
I
N
J
K
H
A
F
E
M
B
C
D
100
100
98
48
52
57
98
100
100
88
100
10
65
52
52
99
31
15
55
65
27
46
UGT84A1
UGT84B1
UGT75D1
UGT74B1
UGT74F2
UGT85A1
UGT83A1
UGT82A1
UGT87A1
UGT86A1
UGT76C1
UGT76C2
UGT91C1
UGT78D1
UGT72B1
UGT72E2
UGT71B6
UGT71C1
UGT92A1
UGT89B1
UGT90A2
UGT73C2
UGT73B2
LhsUGT
A. thaliana family1 UGTs are divided into 14 different functional
groups represented by A - N. The representative UGTs are
shown in each group. Boldface letters represent UGTs from L.
heterophyllus. GenBank accession numbers: UGT84A1 (XP_
002868202.1)ꎻ UGT84A2 ( XP_002883311.1 )ꎻ UGT84B1 (NP_
179907.1)ꎻ UGT75D1 (O23406. 2)ꎻ UGT74B1 (NP_173820.1)ꎻ
UGT74F2 (NP_181910.1)ꎻ UGT85A1 (NP_173656.1)ꎻ UGT83A1
(Q9SGA8.1)ꎻ UGT82A1 (Q9LHJ2.1)ꎻ UGT87A1 (O64732.1)ꎻ
UGT86A1 (Q9SJL0.1)ꎻ UGT76C1 (NP_196206.1)ꎻ UGT76C2 (NP_
196205.1)ꎻ UGT91C1 (Q9LTA3.1)ꎻ UGT78D1 (NP_564357.1)ꎻ
UGT72B1 (Q9M156.1 )ꎻ UGT72E2 (NP_201470.1 )ꎻ UGT71B6
(NP_ 188815.2 )ꎻ UGT71C1 (NP_ 180536.1)ꎻ UGT92A1
(Q9LXV0.1)ꎻ UGT89B1 (NP_177529.2)ꎻ UGT90A2 (Q9SY84.1)ꎻ
UGT73C2 (NP_181214.1)ꎻ UGT73B2 (XP_002867134.1) .
Fig.4  Phylogenetic tree analysis of UGTs from
Leonurus heterophyllus and Arabidopsis thaliana
The identity of LhsUGT with model ̄template ( SMTL id =
2PQ6.A) is 31􀆰36%.
Fig. 5  Tertiary structure prediction of LhsUGT
1
170
130
100
70
55
40
35
25
15
10
2 3 4 5 6 7
1 2 3 4 5 6 7
A
B
kD
A and B are SDS ̄PAGE and Western blot analysis of total
cellular protein under induced conditions in time gradientꎬ
respectively. Lane 1 shows the protein molecular weight
markersꎻ Lanes 2 -7 indicate 0 -5 h after induction with
0􀆰 5 mmol / L IPTG at 27℃ꎬ respectively. Arrow represents
the target bands.
Fig.6  Expression analysis of recombinant LhsUGT
in E. coli BL21 (DE3)
literature search on the UGTs of group L to pre ̄
dict the function of LhsUGT. Results indicated
that LhsUGT can probably glycosylate simple
phenolic compounds as other UGTs in group L
can catalyze simple phenolic compounds to
glycosylationꎬ such as Nicotiana tabacum UGT
(AF190634)ꎬ Rauvolfia serpentine UGT (Q9AR73)ꎬ
Rhodiola sachalinensis UGT (EF508689) [24-26] .
Tyrosol is one of the simple phenolic compounds
that might be glycosylated into salidroside by L.
heterophyllus.
A prokaryotic expression system of LhsUGT
was successfully constructed in this studyꎬ which
lays the foundation to help determine its function
in vitro as well as produce valuable secondary
metabolites via its biosynthesis in the future.
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(责任编辑: 刘艳玲)
504  第 3期                      徐德宏等: 益母草糖基转移酶基因的克隆及原核表达分析(英文)