THE STRUCTURE OF THE CYCLIC ENTEROBACTERIAL COMMON ANTIGEN (ECA) FROMYERSINIA-PESTIS

Two antigenic acidic polysaccharides related to enterobacterial common antigen (ECA) were isolated from a vaccine strain of a pathogenic mic roorganism Yersinia pestis. The low molecular weight polysaccharide (L MP) is composed of equal amounts of 2-acetamido-2-deoxy-D-mannuronic a cid, 4-acetamido-4,6-dideoxy-D-galactose (Fuc4NAc), and 2-amino-2-deox y-D-glucose which is partially N- and partially 6-O-acetylated. The st ructure of the trisaccharide repeating unit was established by analyse s of LMP and the completely N-acetylated LMP (LMP-NAc) using H-1 and C -13 NMR spectroscopy, including 2D COSY and 1D NOE spectroscopy. Deami nation of LMP with nitrous acid gave a set of oligomers terminated wit h 2,5-anhydromannose and ranging from tri- to dodeca-saccharides, thus indicating a random distribution of free amino groups. FABMS analyses of LMP and LMP-NAc showed that LMP consists mainly of the cyclic tetr amer of the trisaccharide repeating unit together with a small amount of the cyclic trimer and a very small amount of the cyclic pentamer an d has, thus, the following structure: [GRAPHICS] where R is Ac or H (s imilar to 1:1), R' is Ac or H(similar to 1:4), and n = 4 (major), 3, 5 (minor). Small proportions of the linear trimer and the linear tetram er were also detected in the preparations. The high molecular weight p olysaccharide is linear and has the same (or a very similar) repeating unit as LMP.