Back C R, Douglas S K, Emerson J E, Nobbs A H, Jenkinson H F
School of Oral and Dental Sciences, University of Bristol, Bristol, UK.
Mol Oral Microbiol. 2015 Oct;30(5):411-24. doi: 10.1111/omi.12106. Epub 2015 Jun 9.
Streptococcus gordonii SspA and SspB proteins, members of the antigen I/II (AgI/II) family of Streptococcus adhesins, mediate adherence to cysteine-rich scavenger glycoprotein gp340 and cells of other oral microbial species. In this article we investigated further the mechanism of coaggregation between S. gordonii DL1 and Actinomyces oris T14V. Previous mutational analysis of S. gordonii suggested that SspB was necessary for coaggregation with A. oris T14V. We have confirmed this by showing that Lactococcus lactis surrogate host cells expressing SspB coaggregated with A. oris T14V and PK606 cells, while L. lactis cells expressing SspA did not. Coaggregation occurred independently of expression of A. oris type 1 (FimP) or type 2 (FimA) fimbriae. Polysaccharide was prepared from cells of A. oris T14V and found to contain 1,4-, 4,6- and 3,4-linked glucose, 1,4-linked mannose, and 2,4-linked galactose residues. When immobilized onto plastic wells this polysaccharide supported binding of L. lactis expressing SspB, but not binding of L. lactis expressing other AgI/II family proteins. Purified recombinant NAVP region of SspB, comprising amino acid (aa) residues 41-847, bound A. oris polysaccharide but the C-domain (932-1470 aa residues) did not. A site-directed deletion of 29 aa residues (Δ691-718) close to the predicted binding cleft within the SspB V-region ablated binding of the NAVP region to polysaccharide. These results infer that the V-region head of SspB recognizes an actinomyces polysaccharide ligand, so further characterizing a lectin-like coaggregation mechanism occurring between two important primary colonizers.
戈登氏链球菌SspA和SspB蛋白是链球菌粘附素抗原I/II（AgI/II）家族的成员，介导与富含半胱氨酸的清道夫糖蛋白gp340以及其他口腔微生物物种的细胞的粘附。在本文中，我们进一步研究了戈登氏链球菌DL1与口腔放线菌T14V之间的共聚机制。先前对戈登氏链球菌的突变分析表明，SspB是与口腔放线菌T14V共聚所必需的。我们通过以下实验证实了这一点：表达SspB的乳酸乳球菌替代宿主细胞与口腔放线菌T14V和PK606细胞共聚，而表达SspA的乳酸乳球菌细胞则不发生共聚。共聚的发生与口腔放线菌1型（FimP）或2型（FimA）菌毛的表达无关。从口腔放线菌T14V细胞中制备了多糖，发现其含有1,4-、4,6-和3,4-连接的葡萄糖、1,4-连接的甘露糖以及2,4-连接的半乳糖残基。当固定在塑料孔上时，这种多糖支持表达SspB的乳酸乳球菌的结合，但不支持表达其他AgI/II家族蛋白的乳酸乳球菌的结合。纯化的SspB重组NAVP区域，包含氨基酸（aa）残基41 - 847，能结合口腔放线菌多糖，但C结构域（932 - 1470 aa残基）则不能。在SspB V区域内靠近预测结合裂隙处进行的29个aa残基（Δ691 - 718）的定点缺失消除了NAVP区域与多糖的结合。这些结果表明，SspB的V区域头部识别放线菌多糖配体，从而进一步阐明了两种重要的早期定植菌之间发生的类似凝集素的共聚机制。
