title: Genetic and structural identification of an O-acyltransferase gene (oacC) responsible for the 3/4-O-acetylation on rhamnose III in Shigella flexneri serotype 6.
abstract: BACKGROUND
  O-antigen (O-polysaccharide) of the lipopolysaccharide is a highly variable cell component of the outer membrane in Shigella flexneri. It defines the serospecificity and plays an important role in the pathogenesis of shigellosis. There are two distinct O-antigen forms for the 19 serotypes of S. flexneri: one for serotypes 1-5, X, Y, 7 (and their subtypes), and the other for serotype 6. Although having different basal O-polysaccharide structures, the two forms share a common disaccharide fragment [→2)-α-l-Rhap III-(1 → 2)-α-l-Rhap II]. In serotype 6 and some non-6 serotypes, RhaIII is O-acetylated at position either 3 or 4 (3/4-O-acetylation), conferring to the hosts a novel antigenic determinant named O-factor 9. An acyltransferase gene (oacB) responsible for this modification has been identified in serotypes 1a, 1b, 2a, 5a, and Y, but not in serotype 6.
  
  
  RESULTS
  Using genetic, serological, and chemical approaches, another acyltransferase gene named oacC was demonstrated to be responsible for the 3/4-O-acetylation on RhaIII in the O-antigen of S. flexneri serotype 6. Inactivation of the oacC gene resulted in the loss of the 3/4-O-acetyltion, and the cloned oacC gene restored this modification upon transformation. In accordance with the similarity in the acceptor substrate structure and high sequence homology (72% identity) between oacC and oacB, oacC has the interchangeable function with the oacB gene in mediation of the 3/4-O-acetylation. The oacC gene is located in a prophage on the chromosome and presented in all 77 serotype 6 strains tested.
  
  
  CONCLUSIONS
  Identification and functional characterization of the O-acetyltransferase encoding gene, oacC, shows that it is involved in O-antigen modification by 3/4-O-acetylation on RhaIII specific to serotype 6.
authors.forename: Yuriy A
authors.initials: YA
authors.lastname: Knirel
authors.forename: Jianping
authors.initials: J
authors.lastname: Wang
authors.forename: Xia
authors.initials: X
authors.lastname: Luo
authors.forename: Sofya N
authors.initials: SN
authors.lastname: Senchenkova
authors.forename: Ruiting
authors.initials: R
authors.lastname: Lan
authors.forename: Anna M
authors.initials: AM
authors.lastname: Shpirt
authors.forename: Pengcheng
authors.initials: P
authors.lastname: Du
authors.forename: Alexander S
authors.initials: AS
authors.lastname: Shashkov
authors.forename: Nan
authors.initials: N
authors.lastname: Zhang
authors.forename: Jianguo
authors.initials: J
authors.lastname: Xu
authors.forename: Qiangzheng
authors.initials: Q
authors.lastname: Sun
mesh_terms: D000107:Acetylation; D000217:Acyltransferases / Q000235:genetics / Q000378:metabolism*; D019081:O Antigens / Q000378:metabolism*; D012210:Rhamnose / Q000378:metabolism*; D065288:Serogroup; D012763:Shigella flexneri / Q000145:classification / Q000201:enzymology* / Q000235:genetics
chemical_list: D019081:O Antigens; D000217:Acyltransferases; D012210:Rhamnose