Structure and epitope characterisation of the O-specific polysaccharide of Proteus mirabilis O28 containing amides of D-galacturonic acid with L-serine and L-lysine.

The O-specific polysaccharide of Proteus mirabilis O28 was found to contain D-galactose, D-galacturonic acid (GalA), 2-acetamido-2-deoxy-D-glucose, L-serine, L-lysine, and O-acetyl groups in molar ratios 1:2:1:1:1:1, the amino acids being linked via their alpha-amino group to the carboxyl group of GalA. The polysaccharide was studied using 1H- and 13C-NMR spectroscopy, including selective spin-decoupling, one-dimensional total correlation spectroscopy, two-dimensional homonuclear correlation spectroscopy (COSY), heteronuclear 13C,1H COSY, one-dimensional NOE, and two-dimensional rotating-frame NOE spectroscopy and partial acid hydrolysis followed by borohydride reduction, methylation, and GLC/MS analysis of the derived glycosyl alditols. The following structure of the repeating unit was established: [formula: see text] Epitope specificity of the P. mirabilis O28 polysaccharide was analysed using a homologous rabbit polyclonal antiserum in quantitative precipitation, passive immunohemolysis, and inhibition of passive immunohemolysis. Study with related synthetic glycopolymers (2-acrylamidoethyl glycosides of amides of alpha-D-GalA with amino acids copolymerised with acrylamide) showed the importance of D-GalA(L-Lys) for manifesting serological specificity of the O-antigen. Serological cross-reactions between P. mirabilis O28, S1959, and R14/S1959 (a transient-like form) are discussed.