ABSTRACT
Modification of the lipopolysaccharide O-antigen of Shigella converts the serotype, which is significant as acquired immune responses are serotype specific. Glucosyltransferases (Gtrs) modify the O-antigen by the addition of glucosyl-groups; however the precise mechanism of O-antigen modification is not fully understood. This study aims to substantiate inferences made on the GtrV topological structure using the substituted cysteine accessibility method (SCAM). Twenty-one amino acid residues were tested to clarify three features of GtrV: the extramembrane regions, a proposed reentrant loop, and a membrane border region. Overall, the results agreed with a previous topology proposed for GtrV. The topology of GtrV consists of 11 extramembrane regions with a cytoplasmic N-terminus, periplasmic C-terminus and 9 transmembrane (TM) helices. The existence of a reentrant loop between TM helices IV and V was verified, and the cytoplasmic membrane border region of TM helix II was examined in depth.
