Korotkov Konstantin V, Pardon Els, Steyaert Jan, Hol Wim G J
Department of Biochemistry, Biomolecular Structure Center, University of Washington, Seattle, WA 98195, USA.
Structure. 2009 Feb 13;17(2):255-65. doi: 10.1016/j.str.2008.11.011.
Secretins are among the largest bacterial outer membrane proteins known. Here we report the crystal structure of the periplasmic N-terminal domain of GspD (peri-GspD) from the type 2 secretion system (T2SS) secretin in complex with a nanobody, the VHH domain of a heavy-chain camelid antibody. Two different crystal forms contained the same compact peri-GspD:nanobody heterotetramer. The nanobody contacts peri-GspD mainly via CDR3 and framework residues. The peri-GspD structure reveals three subdomains, with the second and third subdomains exhibiting the KH fold which also occurs in ring-forming proteins of the type 3 secretion system. The first subdomain of GspD is related to domains in phage tail proteins and outer membrane TonB-dependent receptors. A dodecameric peri-GspD model is proposed in which a solvent-accessible beta strand of the first subdomain interacts with secreted proteins and/or T2SS partner proteins by beta strand complementation.
分泌素是已知最大的细菌外膜蛋白之一。在此，我们报道了来自2型分泌系统（T2SS）分泌素的GspD周质N端结构域（peri-GspD）与纳米抗体（重链骆驼科抗体的VHH结构域）复合物的晶体结构。两种不同的晶体形式包含相同的紧密peri-GspD：纳米抗体异源四聚体。纳米抗体主要通过互补决定区3（CDR3）和构架残基与peri-GspD接触。peri-GspD结构揭示了三个亚结构域，其中第二和第三亚结构域呈现出KH折叠，这种折叠也出现在3型分泌系统的成环蛋白中。GspD的第一个亚结构域与噬菌体尾部蛋白和外膜TonB依赖性受体中的结构域相关。我们提出了一个十二聚体peri-GspD模型，其中第一个亚结构域的一个溶剂可及β链通过β链互补与分泌蛋白和/或T2SS伴侣蛋白相互作用。
