Paik Sehmi, Brown Arunsri, Munro Cindy L, Cornelissen Cynthia Nau, Kitten Todd
The Philips Institute of Oral and Craniofacial Molecular Biology, Virginia Commonwealth University, Richmond, Virginia 23298, USA.
J Bacteriol. 2003 Oct;185(20):5967-75. doi: 10.1128/JB.185.20.5967-5975.2003.
Streptococcus mutans belongs to the viridans group of oral streptococci, which is the leading cause of endocarditis in humans. The LraI family of lipoproteins in viridans group streptococci and other bacteria have been shown to function as virulence factors, adhesins, or ABC-type metal transporters. We previously reported the identification of the S. mutans LraI operon, sloABCR, which encodes components of a putative metal uptake system composed of SloA, an ATP-binding protein, SloB, an integral membrane protein, and SloC, a solute-binding lipoprotein, as well as a metal-dependent regulator, SloR. We report here the functional analysis of this operon. By Western blotting, addition of Mn to the growth medium repressed SloC expression in a wild-type strain but not in a sloR mutant. Other metals tested had little effect. Cells were also tested for aerobic growth in media stripped of metals then reconstituted with Mg and either Mn or Fe. Fe at 10 micro M supported growth of the wild-type strain but not of a sloA or sloC mutant. Mn at 0.1 micro M supported growth of the wild-type strain and sloR mutant but not of sloA or sloC mutants. The combined results suggest that the SloABC proteins transport both metals, although the SloR protein represses this system only in response to Mn. These conclusions are supported by (55)Fe uptake studies with Mn as a competitor. Finally, a sloA mutant demonstrated loss of virulence in a rat model of endocarditis, suggesting that metal transport is required for endocarditis pathogenesis.
变形链球菌属于口腔链球菌中的草绿色链球菌群，是人类心内膜炎的主要病因。草绿色链球菌群及其他细菌中的LraI脂蛋白家族已被证明可作为毒力因子、黏附素或ABC型金属转运蛋白发挥作用。我们之前报道了变形链球菌LraI操纵子sloABCR的鉴定，该操纵子编码一个假定的金属摄取系统的组成部分，包括一个ATP结合蛋白SloA、一个整合膜蛋白SloB、一个溶质结合脂蛋白SloC，以及一个金属依赖性调节因子SloR。我们在此报告该操纵子的功能分析。通过蛋白质免疫印迹法，向生长培养基中添加锰可抑制野生型菌株中SloC的表达，但在sloR突变体中则不会。所测试的其他金属影响很小。还对细胞在去除金属后用镁以及锰或铁重新配制的培养基中的需氧生长情况进行了测试。10微摩尔的铁支持野生型菌株的生长，但不支持sloA或sloC突变体的生长。0.1微摩尔的锰支持野生型菌株和sloR突变体的生长，但不支持sloA或sloC突变体的生长。综合结果表明，SloABC蛋白可转运这两种金属，尽管SloR蛋白仅在对锰作出反应时才抑制该系统。这些结论得到了以锰作为竞争者的(55)铁摄取研究的支持。最后，一个sloA突变体在大鼠心内膜炎模型中表现出毒力丧失，这表明金属转运是心内膜炎发病机制所必需的。
