Ma Y, Lassiter M O, Banas J A, Galperín M Y, Taylor K G, Doyle R J
Department of Microbiology and Immunology, Academic Health Center, University of Louisville, Kentucky 40292, USA.
J Bacteriol. 1996 Mar;178(6):1572-7. doi: 10.1128/jb.178.6.1572-1577.1996.
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 alpha-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 alpha-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 alpha-1,6 glucans, the 60-kDa protein is probably the lectin needed for glucan-dependent cellular aggregation.
远缘链球菌培养上清液中的几种蛋白质能够与葡聚糖凝胶G-75紧密结合。这些蛋白质可以被低分子量的α-1,6葡聚糖部分洗脱，或被4M盐酸胍完全洗脱。洗脱曲线很复杂，得到了分子量为16、45、58至60、90、135和145kDa的蛋白质，表明野生型菌株拥有多种葡聚糖结合蛋白。分离出了两种不能被高分子量α-1,6葡聚糖聚集的远缘链球菌突变体。一个突变体是自发产生的，来自添加了葡聚糖的细胞悬液，而另一个是由甲磺酸乙酯诱导产生的。如培养上清液和全细胞的凝胶电泳所示，两种突变体都缺乏一种60kDa的蛋白质。氨基酸分析表明，58至60kDa的蛋白质和90kDa的蛋白质是不同的，尽管两者的N端都被封闭。两种突变体在蔗糖存在下仍保留其粘附于玻璃的能力以及发酵甘露醇和山梨醇的能力。如活性凝胶所示，两种突变体都保留了其葡糖基转移酶活性。使用针对变形链球菌葡聚糖结合蛋白的抗体进行的蛋白质印迹（免疫印迹）未显示与远缘链球菌蛋白质的交叉反应性。结果表明，即使远缘链球菌产生几种能够结合α-1,6葡聚糖的蛋白质，60kDa的蛋白质可能是葡聚糖依赖性细胞聚集所需的凝集素。
