MENINGOCOCCAL PILIN - A GLYCOPROTEIN SUBSTITUTED WITH DIGALACTOSYL 2,4-DIACETAMIDO-2,4,6-TRIDEOXYHEXOSE

Neisseria meningitidis pili are filamentous protein structures that ar e essential adhesins in capsulate bacteria. Pili of adhesion variants of meningococcal strain C311 contain glycosyl residues on pilin (PilE) , their major structural subunit, Despite the presence of three potent ial N-linked glycosylation sites, none appears to be occupied in these pilins. Instead, a novel O-linked trisaccharide substituent, not prev iously found as a constituent of glycoproteins, is present within a pe ptide spanning amino acid residues 45 to 73 of the PilE molecule, This structure contains a terminal 1-4-linked digalactose moiety covalentl y linked to a 2,4-diacetamido-2,4,6-trideoxyhexose sugar which is dire ctly attached to pilin, Pilins derived from galactose epimerase (galE) mutants lack the digalactosyl moiety, but retain the diacetamidotride oxyherose substitution. Both parental (#3) pilins and those derived fr om a hyper-adherent variant (#16) contained identical sugar substituti ons in this region of pilin, and galE mutants of #3 were similar to th e parental phenotype in their adherence to host cells. These studies h ave confirmed our previous observations that meningococcal pili are gl ycosylated and provided the first structural evidence for the presence of covalently linked carbohydrate on pili. In addition, they have rev ealed a completely novel protein/saccharide linkage.