OLIGOSACCHARIDE-RECEPTOR INTERACTION OF THE GAL-ALPHA-1-4GAL BINDING ADHESIN OF STREPTOCOCCUS-SUIS - COMBINING SITE ARCHITECTURE AND CHARACTERIZATION OF 2 VARIANT ADHESIN SPECIFICITIES

The sugar binding specificities of two groups of Streptococcus suis, a pig pathogen that causes meningitis also in man, were determined. Bot h the group represented by a recently characterized strain inhibitable by galactose and N-acetylgalactosamine (type P-N) and the group inhib itable by galactose (type P-O) were found by hemagglutination and soli d-phase binding inhibition experiments to recognize the disaccharide G al alpha 1-4Gal of the P-1 and P-k blood group antigens. Both types pr eferred the disaccharide in terminal position. P-N showed some, wherea s P-O showed almost no, binding to the globoside oligosaccharide conta ining an additional GalNAc beta 1-3 residue. The complete hydrogen bon ding patterns were determined by using deoxy and other synthetic deriv atives of the receptor disaccharide, and the constructed models of the interactions were compared with that of Escherichia coli PapG(396) ad hesin. The essential hydroxyls for binding were the HO-4', HO-6', HO-2 , and HO-3 hydroxyls on the beta' alpha-side of the Gal alpha 1-4Gal m olecule. Type P, adhesin also formed weak interactions with the hydrox yls HO-6 and HO-3'. The mechanism differed from that of E. coli, which binds to a cluster of five hydroxyls (HO-6, HO-2', HO-3', HO-4', and HO-6') and thus to a different part of the receptor disaccharide. Thes e results represent the first example of the comparison of the sacchar ide receptor hydrogen bonding patterns of two bacterial organisms of d ifferent origin and show that the same saccharide may be recognized by two different binding mechanisms.