Kilic Ali O, Honeyman Allen L, Tao Lin
Department of Oral Biology, College of Dentistry, University of Illinois at Chicago, IL 60612, USA.
FEMS Microbiol Lett. 2007 Jan;266(2):218-23. doi: 10.1111/j.1574-6968.2006.00522.x.
Sugar metabolism by Streptococcus mutans is associated with tooth decay. The most abundant sugars in the human diet are sucrose and maltose, a derivative of starch. Previously, we reported a binding protein-dependent transport system (msm) in S. mutans that transports sucrose and maltose, but its associated enzymes do not metabolize maltose. By searching the S. mutans genomic sequence for a maltose system (mal), we found a gene cluster encoding proteins with homology to those of msm and the Escherichia coli maltose system. Mutants were constructed by deleting msm or mal, or both, and tested for sugar utilization. Deletion of the mal system diminished the ability of S. mutans to ferment maltose, but deletion of only the mal transporter genes or msm showed reduced utilization of chromogenic maltosides. Maltose, sucrose, glucose, fructose, mannose, and N-acetyl glucosamine inhibited utilization of chromogenic maltosides by the wild-type strain and mutants. In conclusion, the two binding protein-dependent systems in S. mutans appear to transport collaboratively their common substrate sugars, notably sucrose and maltose.
变形链球菌的糖代谢与龋齿相关。人类饮食中最丰富的糖类是蔗糖和麦芽糖（淀粉的一种衍生物）。此前，我们报道了变形链球菌中一种依赖结合蛋白的转运系统（msm），该系统可转运蔗糖和麦芽糖，但其相关酶不能代谢麦芽糖。通过在变形链球菌基因组序列中搜索麦芽糖系统（mal），我们发现了一个基因簇，其编码的蛋白质与msm和大肠杆菌麦芽糖系统的蛋白质具有同源性。通过缺失msm或mal，或两者同时缺失来构建突变体，并对其糖利用情况进行测试。mal系统的缺失降低了变形链球菌发酵麦芽糖的能力，但仅缺失mal转运蛋白基因或msm时，对生色麦芽糖苷的利用减少。麦芽糖、蔗糖、葡萄糖、果糖、甘露糖和N-乙酰葡糖胺抑制野生型菌株和突变体对生色麦芽糖苷的利用。总之，变形链球菌中的两个依赖结合蛋白的系统似乎协同转运它们的共同底物糖，特别是蔗糖和麦芽糖。
