Anti-Adhesins of Streptococcus Sobrinus

Abstract

Several members of the genus Streptococcus seem to be able to elaborate surface lectins. The oral streptococci have been reported to bind sialic acid ( S. sanguis) and α-glucans (Gibbons and Fitzgerald 1969). The organisms capable of binding α-glucans include S. cricetus and S. sobrinus. A few members of the highly cariogenic S. mutans also can complex with glucans. Most oral streptococci are also capable of interacting with α-glucans via lectin-independent sites (Robyt, 1995; Mooser, 1992). In the lectin-independent interactions, glucan synthases (dextransucrases or glucosyltransferases, GTFs) use glucans as acceptors for chain extension. The glucan-binding sites on these enzymes are distinct from the catalytic sites acting on sucrose, the sole and natural substrate of the enzymes (Mooser, 1992; Mooser and Wong, 1988; Robyt, 1982).). In the presence of sucrose, streptococci are able to adhere to and colonize enamel surfaces leading to dental decay. Adhesion is a first step leading to dental caries. There have been numerous studies in the past few decades describing adhesion mechanisms of oral streptococci. If suitable anti-adhesins were available, it follows that bacterial colonization could be prevented. There are several factors which modify oral microbial adhesion, including antibodies, lysozyme, salivary amylase, salivary proteins (statherin and proline-rich proteins, PRPs), and resident microbiota capable of producing proteases and glycosidases. Some of the above named factors promote adhesion, whereas others inhibit streptococcal binding to enamel. In this paper, results are presented which show that an anti-adhesin of S. sobrinus, periodate-oxidized α-1,6 glucan, is a potent anti-caries agent. The periodate-oxidized glucan not only inhibits glucan-binding lectin (GBL) activities, but also is an inhibitor of streptococcal GTFs.