Peptidoglycan and lipopolysaccharide bind to the same binding site on lymphocytes (original) (raw)

Abstract

Bacterial cell wall peptidoglycan (PGN) and lipopolysaccharide (LPS), which are both macrophage activators and polyclonal B cell mitogens, were shown to bind to the same dominant 70-kDa 6.5 PI protein on the surface of mouse B lymphocytes. This conclusion was supported by the following results: (a) the PGNand LPS-binding proteins co-migrated following photoaffinity cross-linking and two-dimensional polyacrylamide gel electrophoresis; (b) cross-linking of PGN to this 70-kDa protein was competitively inhibited by LPS (ICs0 = 7.3 p~) , LPS from a deep rough mutant (ICs0 = 6.9 p~) , and lipid A (ICso = 18-72 p~) ; (c) cross-linking of LPS to this 70-kDa protein was competitively inhibited by polymeric soluble PGN (Iceo = 0.09 p~) and sonicated high M, PGN (ICs0 = 0.6 p~) ; (d) cross-linking of both PGN and LPS to this 70-kDa protein was also competitively inhibited by dextran sulfate (ICs0 = 115-124 p~) ; (e) cross-linking of both PGN and LPS to this 70-kDa protein was inhibited by a (GlcNAc)z-specific lectin; and (f) peptide maps of the 70-kDa proteins digested with chymotrypsin, subtilisin, staphylococcal protease V, or papain were identical for PGN-and LPS-binding proteins and unique for each enzyme. Based on competitive inhibition experiments, binding of PGN to the 70-kDa protein was 20-1200 times stronger than the binding of LPS or lipid A on a per mol basis. However, when aggregated micellar structures of LPS or lipid A were considered, the avidities of LPS and PGN binding were similar. These results demonstrate binding of PGN and LPS to the same 70-kDa protein on lymphocytes and suggest that the binding is specific for the (GlcNAc-MurNAc), backbone of PGN and the (GlcNAc)z part of lipid A. Peptidoglycan (PGN)' is the major cell wall constituent of all bacteria (1). Lipopolysaccharide (LPS) is the major constituent of the outer membrane layer of the cell wall of Gramnegative bacteria (2). Several in vivo effects of PGN and LPS are strikingly similar: they both can reproduce most of the major signs and symptoms associated with bacterial infections (fever, inflammation, leukocytosis, macrophage and lympho

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