Department of Odontology, Umeå University, Umeå, Sweden.
J Mol Biol. 2010 Apr 2;397(3):740-51. doi: 10.1016/j.jmb.2010.01.065. Epub 2010 Feb 4.
Streptococcus gordonii is a primary colonizer and is involved in the formation of dental plaque. This bacterium expresses several surface proteins. One of them is the adhesin SspB, which is a member of the Antigen I/II family of proteins. SspB is a large multi-domain protein that has interactions with surface molecules on other bacteria and on host cells, and is thus a key factor in the formation of biofilms. Here, we report the crystal structure of a truncated form of the SspB C-terminal domain, solved by single-wavelength anomalous dispersion to 1.5 A resolution. The structure represents the first of a C-terminal domain from a streptococcal Antigen I/II protein and is comprised of two structurally related beta-sandwich domains, C2 and C3, both with a Ca(2+) bound in equivalent positions. In each of the domains, a covalent isopeptide bond is observed between a lysine and an asparagine, a feature that is believed to be a common stabilization mechanism in Gram-positive surface proteins. S. gordonii biofilms contain attachment sites for the periodontal pathogen Porphyromonas gingivalis and the SspB C-terminal domain has been shown to have one such recognition motif, the SspB adherence region. The motif protrudes from the protein, and serves as a handle for attachment. The structure suggests several additional putative binding surfaces, and other binding clefts may be created when the full-length protein is folded.
戈登链球菌是一种主要的定植菌，参与牙菌斑的形成。该细菌表达几种表面蛋白。其中一种是黏附素 SspB，它是抗原 I/II 家族蛋白的成员。SspB 是一种大型多结构域蛋白，与其他细菌和宿主细胞表面分子相互作用，因此是生物膜形成的关键因素。在这里，我们报道了通过单波长反常分散法解决到 1.5A 分辨率的 SspB C 端结构域截断形式的晶体结构。该结构代表了第一个来自链球菌抗原 I/II 蛋白的 C 端结构域，由两个结构相关的β-三明治结构域 C2 和 C3 组成，两者均在等效位置结合 Ca(2+)。在每个结构域中，观察到赖氨酸和天冬酰胺之间的共价异肽键，这一特征被认为是革兰氏阳性表面蛋白的常见稳定机制。龈卟啉单胞菌生物膜含有牙周病原体牙龈卟啉单胞菌的附着位点，并且已经表明 SspB C 端结构域具有这样的识别基序，即 SspB 附着区域。该基序从蛋白质中突出，充当附着的把手。该结构表明了几个额外的潜在结合表面，并且当全长蛋白质折叠时，可能会形成其他结合裂缝。
