N-linked protein glycosylation is required for full competence in Campylobacter jejuni 81-176

The recent sequencing of the virulence plasmid of Campylobacter jejuni 81-176 revealed the presence of genes homologous to type IV secretion systems (TFSS) that have subsequently been found in Helicobacter pylori and Wolinella succinogenes. Mutational analyses of some of these genes have implicated their involvement in intestinal epithelial cell invasion and natural competence. In this report, we demonstrate that one of these type IV secretion homologs, Cjp3/VirB10, is a glycoprotein. Treatment with various glycosidases and binding to soybean agglutinin indicated that the structure of the glycan present on VirB10 contains a terminal GalNAc, consistent with previous reports of N-linked glycans in C. jejuni. Site-directed mutagenesis of five putative N-linked glycosylation sites indicated that VirB10 is glycosylated at two sites, N32 and N97. Mutants in the N-linked general protein glycosylation (pgl) system of C. jejuni are significantly reduced in natural transformation, which is likely due, in part, to lack of glycosylation of VirB10. The natural transformation defect in a virB10 mutant can be complemented in trans by using a plasmid expressing wild-type VirB10 or an N32A substitution but not by using a mutant expressing VirB10 with an N97A substitution. Taken together, these results suggest that glycosylation of VirB10 specifically at N97 is required for the function of the TFSS and for full competence in C. jejuni 81-176.