Structural and serological studies of the O-specific polysaccharide of the bacterium Proteus mirabilis O10 containing L-altruronic acid, a new component of O-antigens.

An acidic O-specific polysaccharide from the lipopolysaccharide of Proteus mirabilis O10 contains 2-acetamido-2-deoxy-D-glucose, 2-acetamido-2-deoxy-D-galactose, D-galacturonic acid, and L-altruronic acid, the last-named sugar having not been found hitherto in O-antigens. Structure of a branched tetrasaccharide repeating unit of the polysaccharide was established by 1H and 13C NMR spectroscopy, including two-dimensional COSY and rotating-frame NOE spectroscopy. The lateral L-altruronic acid residue plays the immunodominant role in manifestation of the O10 specificity of Proteus, whereas a disaccharide fragment of the main chain in common with the O-specific polysaccharide of P. mirabilis O43 provides the one-way serological cross-reactivity between anti-O10 serum and O43-antigen.