质谱鉴定大肠杆菌O77中WbaD和WbaC糖基转移酶的功能

he wbaD gene and wbaC gene in Escherichia coli O77 O-antigen gene cluster were proposed to encode two distinctmannosyltransferases which together assemble O-antigen oligosaccharide repeat units. In this study, a synthetic acceptorP1-(11-phenoxyundecyl)-P2-(2-acetamido-2-deoxy-α-D-glucopyranosyl) diphosphate(GlcNAc-PP-PhU) was used as an acceptor and GDP-Man as a donor substrate,the activitiesofWbaD and WbaCwere identified and characterizedby detailed structural characterization of their lipooligosacharide enzyme products using high-sensitivity negative-ion electrospray ionization (ESI) collision-induced dissociation tandem mass spectrometry (CID) MS-MS. The extensive fragmentation unequivocally demonstrated that the Man-GlcNAc linkage in wbaD catalyzed reaction product and twoMan-Manlinkages in tandemwbaD/wbaC catalyzed reaction product werepresent, respectively. These results suggest that the O-repeating unit of E.coliO77is biosynthesized from GlcNAc-PP-PhU by successive sugar transferreactions..