The linkage of lysine in the O-specific chains of Proteus mirabilis 1959

Lipopolysaccharides of qualitatively identical but quantitatively different sugar composition were extracted from Proteus mirabilis strain 1959. The lipopolysaccharide with the higher percentage of typical O-specific constituents was subjected to partial acid hydrolysis. An oligosaccharide B22 was separated by paper chromatography and electrophoresis. It was found to be composed of equimolar amounts of D-galacturonic acid, D-galactosamine and L-lysine. Dinitrophenylation of the oligosaccharide as well as of the genuine lipopolysaccharide afforded xi-dinitrophenyl-L-lysine after acid hydrolysis, showing that lysine was linked to the disaccharide via its alpha-amino group. Further studies including the Morgan-Elson and Elson-Morgan reactions, NaBH4-reduction, hydrazinolysis and periodate oxidation revealed the structure of oligosaccharide B22 as D-galacturonyl-(1 leads to 4)-D-galactosamine with lysine attached to the carboxylic group of galacturonic acid via its alpha-amino group. Judged from its high inhibition capacity this oligosaccharide has to be considered as an essential part of the serological determinant of Proteus mirabilis 1959. The frequent occurrence of lysine and galacturonic acid in Proteus mirabilis O-serogroups and their possible significance for the respective serological specificities are discussed.