Department of Microbiology and Molecular Genetics, University of Texas Health Science Center, Houston, TX 77030.
Proc Natl Acad Sci U S A. 2014 Mar 11;111(10):3835-40. doi: 10.1073/pnas.1321417111. Epub 2014 Feb 24.
The formation of dental plaque, a highly complex biofilm that causes gingivitis and periodontitis, requires specific adherence among many oral microbes, including the coaggregation of Actinomyces oris with Streptococcus oralis that helps to seed biofilm development. Here, we report the discovery of a key coaggregation factor for this process. This protein, which we named coaggregation factor A (CafA), is one of 14 cell surface proteins with the LPXTG motif predicted in A. oris MG1, whose function was hitherto unknown. By systematic mutagenesis of each of these genes and phenotypic characterization, we found that the Actinomyces/Streptococcus coaggregation is only abolished by deletion of cafA. Subsequent biochemical and cytological experiments revealed that CafA constitutes the tip of a unique form of the type 2 fimbria long known for its role in coaggregation. The direct and predominant role of CafA in adherence is evident from the fact that CafA or an antibody against CafA inhibits coaggregation, whereas the shaft protein FimA or a polyclonal antibody against FimA has no effect. Remarkably, FimA polymerization was blocked by deletion of genes for both CafA and FimB, the previously described tip protein of the type 2 fimbria. Together, these results indicate that some surface proteins not linked to a pilus gene cluster in Gram-positive bacteria may hijack the pilus. These unique tip proteins displayed on a common pilus shaft may serve distinct physiological functions. Furthermore, the pilus shaft assembly in Gram-positive bacteria may require a tip, as is true for certain Gram-negative bacterial pili.
牙菌斑的形成是一种高度复杂的生物膜，会导致牙龈炎和牙周炎，需要许多口腔微生物之间的特定附着，包括放线菌与口腔链球菌的共聚集，这有助于启动生物膜的发展。在这里，我们报告了这一过程的一个关键共聚因子的发现。这种蛋白质，我们称之为共聚因子 A（CafA），是在 A. oris MG1 中预测的 14 个具有 LPXTG 基序的细胞表面蛋白之一，其功能迄今未知。通过对这些基因的系统诱变和表型特征分析，我们发现只有 cafA 的缺失才会导致放线菌/链球菌的共聚作用完全丧失。随后的生化和细胞学实验表明，CafA 构成了一种独特形式的 2 型菌毛的尖端，这种菌毛长期以来因其在共聚中的作用而闻名。CafA 在黏附中的直接和主要作用从以下事实中显而易见：CafA 或针对 CafA 的抗体抑制共聚，而轴蛋白 FimA 或针对 FimA 的多克隆抗体则没有影响。值得注意的是，CafA 和 FimB 基因的缺失（FimB 是以前描述的 2 型菌毛的尖端蛋白）阻断了 FimA 的聚合。这些结果表明，革兰氏阳性菌中与菌毛基因簇无关的某些表面蛋白可能劫持了菌毛。这些显示在共同菌毛轴上的独特尖端蛋白可能具有不同的生理功能。此外，革兰氏阳性菌中菌毛轴的组装可能需要一个尖端，就像某些革兰氏阴性菌的菌毛一样。
