Structure of a 2-aminoethyl phosphate-containing O-specific polysaccharide of Proteus penneri 63 from a new serogroup O68.

Lipopolysaccharide of Proteus penneri strain 63 was degraded by mild acid to give a high molecular mass O-specific polysaccharide that was isolated by gel-permeation chromatography. Sugar and methylation analyses and NMR spectroscopic studies, including two-dimensional 1H, 1H COSY, TOCSY rotating-frame NOE spectroscopy, H-detected 1H,13C and 1H,31P heteronuclear multiple-quantum coherence (HMQC), and 1H, 13C HMQC-TOCSY experiments, demonstrated the following structure of the polysaccharide: where FucNAc is 2-acetamido-2,6-dideoxygalactose and PEtn is 2-aminoethyl phosphate. The polysaccharide studied shares some structural features, such as the presence of D-GlcNAc6PEtn and an alpha-L-FucNAc-(1-->3)-D-GlcNAc disaccharide, with other Proteus O-specific polysaccharides. A marked cross-reactivity of P. penneri 63 O-antiserum with P. vulgaris O12 was observed and substantiated by a structural similarity of the O-specific polysaccharides of the two strains. In spite of this, the polysaccharide of P. penneri 63 has the unique structure among Proteus O-antigens, and therefore a new, separate serogroup, O68, is proposed for this strain.