Department of Bioengineering, University of Washington, Box 355013, Seattle, WA 98195-5013, USA.
Department of Bioengineering, University of Washington, Box 355013, Seattle, WA 98195-5013, USA.
J Mol Biol. 2018 Oct 12;430(20):3764-3773. doi: 10.1016/j.jmb.2018.07.005. Epub 2018 Jul 10.
Streptococcus mutans is a bacterial species that predominates in the oral microbiome. S. mutans binds to the tooth surface, metabolizes sugars and produces acid, leading to cavity formation. S. mutans can also cause infectious endocarditis. Recent evidence suggests that S. mutans biofilms contain amyloid fibrils. Amyloids are insoluble fibrillar protein aggregates, and bacteria use functional amyloids to improve robustness of their biofilms. While the functional amyloids in bacteria such as Escherichia coli and Staphylococcus aureus have been heavily investigated, little is known about the mechanism of S. mutans amyloid formation. Previous results from our laboratory with the amyloidogenic proteins and peptides from the aforementioned bacteria and other mammalian amyloid systems suggest that amyloid formation progresses via an intermediate that adopts a unique secondary structure-α-sheet. De novo designed peptides with alternating l- and d-amino acid also adopt an α-sheet secondary structure and inhibit amyloid formation by binding to soluble oligomeric species during amyloidogenesis. Inhibition of fibrillization by α-sheet peptides suggests the presence of α-sheet during amyloid formation. To investigate the mechanism of functional amyloid formation in S. mutans, α-sheet peptides were compared to epigallocatechin gallate for their ability to inhibit fibril formation in S. mutans. Inhibition was demonstrated in a biofilm plate assay and on hydroxyapatite surfaces both in S. mutans alone and in bacteria from human saliva. The observed inhibition suggests that an α-sheet mediated mechanism may be operative during functional amyloid formation.
变形链球菌是一种在口腔微生物群中占优势的细菌物种。变形链球菌附着在牙齿表面，代谢糖并产生酸，导致龋齿形成。变形链球菌也可引起感染性心内膜炎。最近的证据表明，变形链球菌生物膜中含有淀粉样纤维。淀粉样纤维是不溶性纤维状蛋白聚集体，细菌利用功能性淀粉样纤维来提高其生物膜的稳健性。尽管大肠杆菌和金黄色葡萄球菌等细菌中的功能性淀粉样纤维已得到深入研究，但对于变形链球菌淀粉样形成的机制知之甚少。我们实验室之前对上述细菌和其他哺乳动物淀粉样系统的淀粉样蛋白和肽的研究结果表明，淀粉样形成通过一种独特的二级结构-α-片层的中间产物进行。具有交替的 l-和 d-氨基酸的从头设计肽也采用α-片层二级结构，并通过在淀粉样形成过程中与可溶性寡聚体结合来抑制淀粉样形成。α-片层肽对原纤维形成的抑制表明在淀粉样形成过程中存在α-片层。为了研究变形链球菌中功能性淀粉样纤维形成的机制，将α-片层肽与表没食子儿茶素没食子酸酯进行比较，以研究它们抑制变形链球菌纤维形成的能力。在生物膜平板测定和羟基磷灰石表面都证明了在单独的变形链球菌和来自人唾液的细菌中抑制纤维形成的能力。观察到的抑制作用表明，在功能性淀粉样纤维形成过程中可能存在α-片层介导的机制。
