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The wciN Gene Encodes an α-1,3-Galactosyltransferase Involved in the Biosynthesis of the Capsule Repeating Unit of Streptococcus pneumoniae Serotype 6B
journal contribution
posted on 2016-02-20, 16:27 authored by Weiqing Han, Li Cai, Baolin Wu, Lei Li, Zhongying Xiao, Jiansong Cheng, Peng G. WangAlmost all Streptococcus pneumoniae (pneumococcus)
capsule serotypes employ the Wzy-dependent pathway for their capsular
polysaccharide (CPS) biosynthesis. The assembly of the CPS repeating
unit (RU) is the first committed step in this pathway. The wciN gene was predicted to encode a galactosyltransferase
involved in the RU assembly of pneumococcus type 6B CPS. Herein, we
provide the unambiguous in vitro biochemical evidence
that wciN encodes an α-1,3-galactosyltransferase
catalyzing the transfer of galactosyl from UDP-Gal onto the Glcα-pyrophosphate-lipid
(Glcα-PP-lipid) acceptor to form Galα(1–3)Glcα-PP-lipid.
A chemically synthesized acceptor (Glcα-PP-O(CH2)10CH3) was used to characterize the WciN activity.
The disaccharide product, i.e., Galα(1–3)Glcα-PP-O(CH2)10CH3, was characterized by mass and
NMR spectroscopy. Substrate specificity study indicated that the acceptor
structural region composed of pyrophosphate and lipid moieties may
play an important role in the enzyme-acceptor recognition. Furthermore,
divalent metal cations were found indispensable to the WciN activity,
suggesting that this glycosyltransferase (GT) belongs to the GT-A
superfamily. By analyzing the activities of six WciN mutants, a DXD
motif involved in the coordination of a divalent metal cation was
identified. This work provides a chemical biology approach to characterize
the activities of pneumococcal CPS GTs in vitro and
will help to better understand the pneumococcal CPS biosynthetic pathway.
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Substrate specificity studyRUGalStreptococcus pneumoniae Serotype 6 BAlmostpneumococcal CPS biosynthetic pathwaydivalent metal cationdivalent metal cationsassemblychemical biology approachacceptorwciN Gene EncodesgalactosyltransferaseencodeNMRWciN activitypneumococcal CPS GTspneumococcus type 6 B CPSGlcDXD
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