State Key Laboratory of Biomembrane and Membrane Biotechnology, Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing, China.
PLoS One. 2011 Jan 27;6(1):e16498. doi: 10.1371/journal.pone.0016498.
The Sec translocase mediates the post-translational translocation of a number of preproteins through the inner membrane in bacteria. In the initiatory translocation step, SecB targets the preprotein to the translocase by specific interaction with its receptor SecA. The latter is the ATPase of Sec translocase which mediates the post-translational translocation of preprotein through the protein-conducting channel SecYEG in the bacterial inner membrane. We examined the structures of Escherichia coli Sec intermediates in solution as visualized by negatively stained electron microscopy in order to probe the oligomeric states of SecA during this process. The symmetric interaction pattern between the SecA dimer and SecB becomes asymmetric in the presence of proOmpA, and one of the SecA protomers predominantly binds to SecB/proOmpA. Our results suggest that during preprotein translocation, the two SecA protomers are different in structure and may play different roles.
Sec 转运酶介导了许多前体蛋白通过细菌内膜的翻译后转运。在起始转运步骤中，SecB 通过与受体 SecA 的特异性相互作用将前体蛋白靶向转运酶。后者是 Sec 转运酶的 ATP 酶，通过细菌内膜中的蛋白导通道 SecYEG 介导前体蛋白的翻译后转运。我们通过负染色电子显微镜观察了大肠杆菌 Sec 中间体在溶液中的结构，以探测 SecA 在这个过程中的寡聚状态。在存在 proOmpA 的情况下，SecA 二聚体和 SecB 之间的对称相互作用模式变得不对称，并且 SecA 单体中的一个主要与 SecB/proOmpA 结合。我们的结果表明，在前体蛋白转运过程中，两个 SecA 单体在结构上可能不同，并且可能发挥不同的作用。
