A 28 kDa protein of normal mouse serum binds lipopolysaccharides of Gram-negative and lipoteichoic acids of Gram-positive bacteria

Abstract

A 28 kDa protein from normal mouse serum known to bind to the inner core region of bacterial lipopolysaccharide (LPS) was found to bind also to bacterial poly(glycerophosphate) lipoteichoic acid (LTA). Twenty-nine preparations of LTA were isolated from 19 different bacterial species, purified, chemically analysed, and tested for their ability to bind the 28 kDa protein in a complement-dependent hemolysis and hemolysis inhibition assay. All but one were active in one or both systems and one half of the preparations were active in both. Reactivity patterns were not strictly correlated with the chemical structure of LTA considering the substitution of the poly(glycerophosphate) chain with alanine ester and glycosyl residues and the type of lipid anchor. The isolated lipid anchor alone was unable to bind the serum factor. Comparing the binding to LTA and LPS from Acinetobacter calcoaceticus indicated complete cross-reactivity of LTA and LPS in various serological approaches. Thus, LPS and LTA which are unique amphiphiles in Gram-negative and Gram-positive bacteria, respectively, share a similar function in terms of binding the 28 kDa mouse serum protein.