CNRS, UMR 5048, Université Montpellier 1 and Université Montpellier 2, Centre de Biochimie Structurale, Montpellier, France.
J Bacteriol. 2012 Nov;194(22):6255-63. doi: 10.1128/JB.01424-12. Epub 2012 Sep 14.
MgtC is a virulence factor of unknown function important for survival inside macrophages in several intracellular bacterial pathogens, including Mycobacterium tuberculosis. It is also involved in adaptation to Mg(2+) deprivation, but previous work suggested that MgtC is not a Mg(2+) transporter. In this study, we demonstrated that the amount of the M. tuberculosis MgtC protein is not significantly increased by Mg(2+) deprivation. Members of the MgtC protein family share a conserved membrane N-terminal domain and a more divergent cytoplasmic C-terminal domain. To get insights into MgtC functional and structural organization, we have determined the nuclear magnetic resonance (NMR) structure of the C-terminal domain of M. tuberculosis MgtC. This structure is not affected by the Mg(2+) concentration, indicating that it does not bind Mg(2+). The structure of the C-terminal domain forms a βαββαβ fold found in small molecule binding domains called ACT domains. However, the M. tuberculosis MgtC ACT domain differs from canonical ACT domains because it appears to lack the ability to dimerize and to bind small molecules. We have shown, using a bacterial two-hybrid system, that the M. tuberculosis MgtC protein can dimerize and that the C-terminal domain somehow facilitates this dimerization. Taken together, these results indicate that M. tuberculosis MgtC does not have an intrinsic function related to Mg(2+) uptake or binding but could act as a regulatory factor based on protein-protein interaction that could be facilitated by its ACT domain.
MgtC 是一种未知功能的毒力因子，对于几种细胞内细菌病原体（包括结核分枝杆菌）在巨噬细胞内的存活非常重要。它还参与适应镁（Mg）缺乏，但之前的工作表明 MgtC 不是镁（Mg）转运体。在这项研究中，我们证明了结核分枝杆菌 MgtC 蛋白的数量不会因 Mg 剥夺而显著增加。MgtC 蛋白家族的成员共享一个保守的膜 N 端结构域和一个更具差异性的细胞质 C 端结构域。为了深入了解 MgtC 的功能和结构组织，我们确定了结核分枝杆菌 MgtC 的 C 端结构域的核磁共振（NMR）结构。该结构不受 Mg 浓度的影响，表明它不结合 Mg。C 端结构域的结构形成了一种 βαββαβ 折叠，存在于小分子结合域中，称为 ACT 结构域。然而，结核分枝杆菌 MgtC 的 ACT 结构域与典型的 ACT 结构域不同，因为它似乎缺乏二聚化和结合小分子的能力。我们使用细菌双杂交系统表明，结核分枝杆菌 MgtC 蛋白可以二聚化，并且 C 端结构域以某种方式促进这种二聚化。总之，这些结果表明，结核分枝杆菌 MgtC 没有与镁摄取或结合相关的固有功能，但可能作为一种基于蛋白质-蛋白质相互作用的调节因子发挥作用，其 ACT 结构域可能有助于这种相互作用。
