Department of Restorative Dentistry and Endodontology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
Department of Bacteriology, Hiroshima University Graduate School of Biomedical and Health Sciences, Hiroshima, Japan.
Microbiol Immunol. 2022 Mar;66(3):145-156. doi: 10.1111/1348-0421.12958. Epub 2022 Feb 22.
Streptococcus mutans, a cariogenic pathogen, adheres to the tooth surface and forms a biofilm. Bacterial cell surface proteins are associated with adherence to substrates. Sortase A (SrtA) mediates the localization of proteins with an LPXTG motif-containing proteins to the cell surface by covalent binding to peptidoglycan. In S. mutans UA159, six SrtA-dependent proteins, SpaP, WapA, WapE, DexA, FruA, and GbpC, were identified. Although some of these proteins were characterized, a comprehensive analysis of the six proteins has not been reported. In this study, we constructed mutants deficient in each of these proteins and the SrtA-deficient mutant. The SrtA-deficient mutant showed drastically decreased binding to salivary components, biofilm formation, bacterial coaggregation activity, hydrophobicity, and cellular matrix binding (collagen type I, fibronectin, and laminin). The SpaP-deficient mutant showed significantly reduced binding to salivary components and partially increased coaggregation with Porphyromonas gingivalis, and decreased hydrophobicity, and collagen binding. The WapA-deficient mutant showed slightly decreased coaggregation with Fusobacterium nucleatum. Although the SrtA-deficient mutant showed drastically altered phenotypes, all SrtA-dependent protein-deficient mutants, except the SpaP-deficient mutant, did not show considerable alterations in binding to salivary components. These results indicate that the six proteins may coordinately contribute to these activities. In addition, using genomic data of 125 S. mutans strains, the amino acid sequences of each surface protein were compared and many variations were found among strains, which may affect the phenotype of cell surface proteins in S. mutans.
变形链球菌是一种致龋病原体，能够黏附于牙齿表面并形成生物膜。细菌表面蛋白与黏附于基质有关。天冬氨酸转肽酶 A（SrtA）通过与肽聚糖的共价结合，介导含有 LPXTG 基序的蛋白定位于细胞表面。在变形链球菌 UA159 中，鉴定出了 6 种 SrtA 依赖性蛋白，分别为 SpaP、WapA、WapE、DexA、FruA 和 GbpC。尽管对其中一些蛋白进行了表征，但尚未对这 6 种蛋白进行全面分析。在本研究中，我们构建了这些蛋白缺失突变体和 SrtA 缺失突变体。SrtA 缺失突变体与唾液成分的结合能力、生物膜形成能力、细菌共聚活性、疏水性和细胞基质结合（I 型胶原、纤连蛋白和层粘连蛋白）显著降低。SpaP 缺失突变体与唾液成分的结合能力显著降低，与牙龈卟啉单胞菌的共聚作用部分增加，疏水性和胶原结合能力降低。WapA 缺失突变体与核梭杆菌的共聚作用略有降低。尽管 SrtA 缺失突变体表现出明显改变的表型，但除 SpaP 缺失突变体外，所有 SrtA 依赖性蛋白缺失突变体与唾液成分的结合均未发生明显改变。这些结果表明这 6 种蛋白可能共同参与了这些活性。此外，利用 125 株变形链球菌的基因组数据，比较了每种表面蛋白的氨基酸序列，发现菌株之间存在许多变异，这可能影响变形链球菌表面蛋白的表型。
