Development of a caries risk assessment system using genetic polymorphisms influencing cariogenicities of mutans streptococci.

变形链球菌被认为与龋齿有很强的相关性。据报道，携带这种细菌的儿童有明显更高的龋齿患病率和发展。变形链球菌可以通过葡聚糖的合成在牙齿表面定植和堆积。在变形链球菌的三种葡糖转移酶中，由GTFB基因编码的GTF-I是合成水不溶性葡聚糖(WIG)最重要的酶。为了探讨GTFB的遗传多样性与假发合成的关系，我们收集了小学生石蜡刺激的唾液，并从这些唾液中分离出了21株变形链球菌。用直接测序的方法测定了这些菌株的GTFB的碱基序列，发现GTF-I在409-427位有ANDVNSNPVVAEQLNWL(19位氨基酸)，在446-454位有DSIRVDAVD(9位氨基酸)，这些序列对GTF-I的酶活性是非常重要的。在GTFB的3‘端有直接重复单元，是葡聚糖结合区。这些重复单位对葡聚糖的合成也很重要。本研究揭示了GTF B编码区和酶催化位置(409-427和446-454)之前的序列在临床分离株中高度保守，一些假发合成较低的菌株在GTF-I的C端存在直接重复单位的缺失。

Streptococcus mutans is considered as strongly associated with dental caries. It was reported that children carrying this bacteria had significantly higher caries prevalence and development. S.mutans can colonize and accumulate on the tooth surface by glucan synthesis. GTF-I coded by gtfB gene is the most important enzyme on water-insoluble glucan (WIG) synthesis among three glucosyltransferase of S.mutans. The aim of this study was to investigate the association between genetic diversity of gtfB and WIG synthesis.We collected paraffin-stimulated saliva from primary schoolchildren, and 21 clinical strains of S.mutans were isolated from these saliva samples. Base sequences of gtfB of these strains were determined by direct sequencing analysis.In these days, it was revealed that GTF-I has ANDVDNSNPVVQAEQLNWL (19 aa) at 409-427 and DSIRVDAVD (9 aa) at 446-454, and these sequences are very important for enzyme activity of GTF-I. There are direct repeating units in 3'-terminal of gtfB, which are glucan binding domain. This repeating units are also important for glucan synthesis.In this study, it was revealed that the sequence preceding the coding region of gtf B and enzymatic catalysis position (409-427 and 446-454) are highly conserved among the clinical isolates and that some strains whose WIG synthesis are low have deletion of direct repeating units in C-terminal of GTF-I.