Institute of Structural and Molecular Biology at UCL and Birkbeck, Malet Street, London WC1E7HX, United Kingdom.
J Bacteriol. 2010 May;192(9):2315-23. doi: 10.1128/JB.01384-09. Epub 2010 Feb 19.
Type IV secretion (T4S) systems are involved in several secretion processes, including secretion of virulence factors, such as toxins or transforming molecules, or bacterial conjugation whereby two mating bacteria exchange genetic material. T4S systems are generally composed of 12 protein components, three of which, termed VirB4, VirB11, and VirD4, are ATPases. VirB4 is the largest protein of the T4S system, is known to play a central role, and interacts with many other T4S system proteins. In this study, we have biochemically characterized the protein TraB, a VirB4 homologue from the pKM101 conjugation T4S system. We demonstrated that TraB is a modular protein, composed of two domains, both able to bind DNA in a non-sequence-specific manner. Surprisingly, both TraB N- and C-terminal domains can bind ATP, revealing a new degenerated nucleotide-binding site in the TraB N-terminal domain. TraB purified from the membrane forms stable dimers and is unable to hydrolyze ATP while, when purified from the soluble fraction, TraB can form hexamers capable of hydrolyzing ATP. Remarkably, both the N- and C-terminal domains display ATP-hydrolyzing activity. These properties define a new class of VirB4 proteins.
IV 型分泌系统（T4S）参与多种分泌过程，包括毒力因子（如毒素或转化分子）的分泌，或细菌接合，其中两个交配细菌交换遗传物质。T4S 系统通常由 12 个蛋白质组成，其中 3 个，称为 VirB4、VirB11 和 VirD4，是 ATP 酶。VirB4 是 T4S 系统中最大的蛋白质，已知它起着核心作用，并与许多其他 T4S 系统蛋白质相互作用。在这项研究中，我们对来自 pKM101 接合 T4S 系统的 VirB4 同源物 TraB 进行了生化特性分析。我们证明 TraB 是一种模块化蛋白，由两个结构域组成，都能够以非序列特异性的方式结合 DNA。令人惊讶的是，TraB 的 N 端和 C 端结构域都可以结合 ATP，揭示了 TraB N 端结构域中存在一个新的退化核苷酸结合位点。从膜中纯化的 TraB 形成稳定的二聚体，不能水解 ATP，而从可溶性部分纯化的 TraB 可以形成能够水解 ATP 的六聚体。值得注意的是，N 端和 C 端结构域都显示出 ATP 水解活性。这些特性定义了一类新的 VirB4 蛋白。
