Sequence Analysis of the Streptococcus mulans Ingbritt dexA Gene Encoding Extracellular Dex&anase

摘要

Mutans streptococci, especially Streptococcus mutans and Streptococcus sobrintts, ar6 closely associated with dental caries. The formation of extracellular glucans from sucrose and the ability to produce acids from a variety of sugars are believed tobe major cariogcnic factors of these bacteria (13, 22). S. mutans is able to produce a water-soluble ghiean (WSG), mainly alpha-1,6-linked glucan, and a water-insoluble glucan (WIG), mainly alpha-l,3-linked glucan (4,1 3). Extracellular dex-tranase produced by S. mutans is an endo-en/yme which cleaves alpha-l,6-linkages in the glucans and produces iso-maltosaccharides as its reaction products from the glucans (13, 18). Although the precise role(s) of extracellular dextranase in the virulence of S. mutans has not yet been clearly understood, the following observations have been reported. Dextranase can partially degrade WIG (11, 40), inhibit synthesis of WIG (32, 40), inhibit the adherence of the S. mutans cells to the'smooth surface of the tooth (12, 32), and inhibit plaque formation and dental caries development (10,27).