Structural and serological studies on the O-antigen of Proteus mirabilis O14, a new polysaccharide containing 2-[(R)-1-carboxyethylamino]ethyl phosphate

An O-specific polysaccharide was obtained by mild acid degradation of Prote us mirabilis O14 lipopolysaccharide (LPS) and found to contain D-galactose, 2-acetamido-2-deoxy-D-glalactose, phosphate, N-(2-hydroxyethyl)-D-alanine (D-AlaEtn), and O-acetyl groups. Studies of the initial and O-deacetylated polysaccharides using one- and two-dimensional H-1- and C-13-NMR spectrosco py, including COSY, TOCSY, NOESY, H-detected H-1, C-13 heteronuclear multip le-quantum coherence, and heteronuclear multiple-bond correlation experimen ts, demonstrated the following structure of the repeating unit: [GRAPHICS] This is the second bacterial polysaccharide reported to contain alpha-D-Gal p6PAlaEtn, whereas the first one was the O-antigen of P. mirabilis EU313 ta ken erroneously as strain PrK 6/57 from the O3 serogroup [Vinogradov, E. V. , Kaca, W., Shashkov, A.S., Krajewska-Pietrasik, D., Rozalski, A., Knirel, Y.A. & Kochetkov, N.K. (1990) Eur. J. Biochem., 188, 645-651]. Anti-(P. mir abilis O14) serum cross-reacted with LPS of P. mirabilis EU313 and vice ver sa in passive hemolysis and ELISA. Absorption of both O-antisera with the h eterologous LPS decreased markedly but did not abolish the reaction with th e homologous LPS. These and chemical data indicated that both strains have similar but not identical O-antigens. Therefore, we propose that P. mirabil is EU313 should belong to a new subgroup of the O14 serogroup.