Isolation and characterisation of a heparosan capsular polysaccharide and a core oligosaccharide from Moraxella...

Moraxella lincolnii is a Gram-negative bacterium that resides in the upper respiratory tract (URT) of humans and may have a role as a member of a protective microbial community. Structural characterisation studies of its outer membrane glycan structures are very limited. We report here the isolation and structural characterisation (NMR, GLC-MS) of a capsular polysaccharide (CPS) and an oligosaccharide (OS) (lipooligosaccharide (LOS)-derived) isolated from strain CCUG 52988. The repeat disaccharide unit of the isolated CPS is unmodified heparosan: [→4)-β-D-GlcpA-(1→4)-α-D-GlcpNAc-(1→]_n, a glycosaminoglycan (GAG) also present in mammalian hosts. The core OS isolated was identified as a branched tetrasaccharide composed of: β-D-Glcp-(1→4)-[β-D-Glcp-(1→6)]-α-D-Glcp-(1→5)-α-Kdo-OH. This core OS structure is without heptose residues and is consistent with previously reported core OS structures from Moraxella spp. Genes encoding homologues of the Lgt6 and Lgt3 glycosyltransferases that catalyse these additions were identified in the genome. Additional glycosyltransferases and other proteins encoded downstream of lgt3 were considered to form the LOS biosynthesis locus. This is the first report of the isolation of CPS and core OS from M. lincolnii.