Multiple glucan-binding proteins of Streptococcus sobrinus

Abstract

Several proteins from culture supernatants of Streptococcus sobrinus were able to bind avidly to Sephadex G-75. The proteins could be partially eluted from the Sephadex by low-molecular-weight ␣-1,6 glucan or fully eluted by 4 M guanidine hydrochloride. Elution profiles were complex, yielding proteins of 16, 45, 58 to 60, 90, 135, and 145 kDa, showing that the wild-type strain possessed multiple glucan-binding proteins. Two mutants of Streptococcus sobrinus incapable of aggregation by high-molecular-weight ␣-1,6 glucan were isolated. One mutant was spontaneous, from a cell suspension to which glucan had been added, whereas the other was induced by ethyl methanesulfonate. Both mutants were devoid of a 60-kDa protein, as shown by gel electrophoresis of culture supernatants and whole cells. Amino acid analysis showed that the 58-to 60-kDa protein and the 90-kDa protein were distinct, although both were N-terminally blocked. Both mutants retained their ability to adhere to glass in the presence of sucrose and to ferment mannitol and sorbitol. Both mutants retained their glucosytransferase activities, as shown by activity gels. Western blots (immunoblots), employing antibody against a glucan-binding protein of Streptococcus mutans, failed to reveal cross-reactivity with S. sobrinus proteins. The results show that even though S. sobrinus produces several proteins capable of binding ␣-1,6 glucans, the 60-kDa protein is probably the lectin needed for glucan-dependent cellular aggregation.Bacterial lectins seem to have evolved for the purpose of permitting the bacteria to adhere to glycoconjugate-containing surfaces. Members of the genus Streptococcus, found in the oral cavities of humans and animals, are able to adhere to a variety of surfaces when incubated in the presence of sucrose. The disaccharide sucrose serves as a substratum for glucosyltransferases (GTFs) to yield glucans rich in ␣-1,6 and/or ␣-1,3 linkages. Many of the streptococci produce glucan-binding lectins (GBLs) or glucan-binding proteins (GBPs). Several years ago, McCabe and colleagues were able to purify streptococcal GBPs by using Sephadex as an affinity matrix (12,16,17). Others have now used similar chromatographic techniques to purify streptococcal GBPs (2,14,22,23,28,29). Banas et al. (3) were able to clone and sequence a GBP from Streptococcus mutans Ingbritt. In addition to GBLs, the streptococcal GTFs possess glucan-binding domains (19,27). Many of the bacteria which possess cell surface GTFs are not aggregated by glucans, suggesting that the GTFs do not act as lectins. The purpose of the present study was to define which surface protein of Streptococcus sobrinus is involved in glucan-dependent aggregation. To avoid confusion, a GBP is defined as any protein capable of binding reversibly to Sephadex, whereas a GBL is defined as any Sephadex-binding protein capable of conferring the ability of the bacteria to be aggregated by ␣-1,6 glucan. It is here shown that S. sobrinus possesses at least five GBPs, but only one of these, the 60-kDa band of ...

Glucan-binding Proteins of the Oral Streptococci

“…After the taxonomic split, it was apparent that S. sobrinus strains more readily aggregated than did strains of S. mutans, and a major GBP from S. sobrinus was designated the glucan-binding lectin (GBL) (Drake et al, 1988). Subsequently, Ma et al (1996) defined GBLs as GBPs that confer upon bacteria the property of aggregation in the presence of exogenous alpha-1,6 glucan. According to this definition, all GTFs and GBLs are glucan-binding proteins, but not all glucan-binding proteins are GTFs or GBLs.…”

Regulation of gbpC Expression in Streptococcus mutans

“…GbpC has been shown to be involved in rapid, dextran (glucan)-dependent aggregation (ddag) of bacteria, a phenomenon in which cells grown in liquid cultures autoaggregate upon exposure to exogenously added dextran, a polysaccharide related to glucan (25,41,42). This ddag phenotype is growth phase independent but depends on the growth conditions (40).…”

Passive Transfer of Immunoglobulin Y Antibody to Streptococcus mutans Glucan Binding Protein B Can Confer Protection against Experimental Dental Caries

“…These cariogenic streptococci then accumulate in the dental biofilm following enzymatic synthesis of extracellular glucans which provide multiple binding sites for glucan binding proteins (GBPs) associated with the bacterial cell. At least six proteins with glucan binding properties (i.e., the ability to bind ␣-1,6-glucan) have been identified in Streptococcus mutans (2,21,23) and Streptococcus sobrinus (10,16,26,31), the two mutans streptococcal species most closely associated with human disease. Three of these GBPs, all from S. mutans, have been cloned and sequenced (GBP-A, GBP-B, and GBP-C).…”