Gene products required for surface expression of the capsular form of the group 1 K antigen in Escherichia coli (09a : K30)

The group 1 K30 antigen from Escherichia coli (O9a:K30) is present on the c ell surface as both a capsular structure composed of high-molecular-weight K30 polysaccharide and as short K30 oligosaccharides linked to lipid A-core in a lipopolysaccharide molecule (K30(LPS)). To determine the molecular pr ocesses that are responsible for the two forms of K antigen, the 16 kb chro mosomal cps region has been characterized, This region encodes 12 gene prod ucts required for the synthesis, polymerization and translocation of the K3 0 antigen. The gene products include four glycosyltransferases responsible for synthesis of the K30 repeat unit; a PST(1) exporter (Wzx), required to transfer lipid-linked K30 units across the plasma membrane to the periplasm ic space; and a K30-antigen polymerase (Wzy). These gene products are typic al of those seen in O-antigen biosynthesis gene clusters and they interact with the lipopolysaccharide translocation pathway to express K30(LPS) on th e cell surface. The same gene products also provide the biosynthetic interm ediates for the capsule assembly pathway, although they are not in themselv es sufficient for synthesis of the K30 capsule. Three additional genes, wza , wzb and wzc, encode homologues to proteins that are encoded by gene clust ers involved in expression of a variety of bacterial exopolysaccharides. Mu tant analysis indicates that Wza and Wzc are required for wild-type surface expression of the capsular structure but are not essential for polymerizat ion and play no role in the translocation of K30LPS These surface expressio n components provide the key feature that distinguishes the assembly system s for O antigens and capsules.