Hand Nicholas J, Klein Reinhard, Laskewitz Anke, Pohlschröder Mechthild
Department of Biology, University of Pennsylvania, 201 Leidy Laboratories, 415 South University Ave., Philadelphia, Pennsylvania 19104, USA.
J Bacteriol. 2006 Feb;188(4):1251-9. doi: 10.1128/JB.188.4.1251-1259.2006.
The majority of secretory proteins are translocated into and across hydrophobic membranes via the universally conserved Sec pore. Accessory proteins, including the SecDF-YajC Escherichia coli membrane complex, are required for efficient protein secretion. E. coli SecDF-YajC has been proposed to be involved in the membrane cycling of SecA, the cytoplasmic bacterial translocation ATPase, and in the stabilizing of SecG, a subunit of the Sec pore. While there are no identified archaeal homologs of either SecA or SecG, many archaea possess homologs of SecD and SecF. Here, we present the first study that addresses the function of archaeal SecD and SecF homologs. We show that the SecD and SecF components in the model archaeon Haloferax volcanii form a cytoplasmic membrane complex in the native host. Furthermore, as in E. coli, an H. volcanii deltasecFD mutant strain exhibits both severe cold sensitivity and a Sec-specific protein translocation defect. Taken together, these results demonstrate significant functional conservation among the prokaryotic SecD and SecF homologs despite the distinct composition of their translocation machineries.
大多数分泌蛋白通过普遍保守的Sec孔道转运进入疏水膜并穿过该膜。包括大肠杆菌膜复合物SecDF - YajC在内的辅助蛋白是高效蛋白质分泌所必需的。有人提出大肠杆菌的SecDF - YajC参与SecA（一种细胞质细菌转运ATP酶）的膜循环以及Sec孔道亚基SecG的稳定。虽然尚未鉴定出SecA或SecG的古菌同源物，但许多古菌拥有SecD和SecF的同源物。在此，我们首次对古菌SecD和SecF同源物的功能进行了研究。我们发现，在模式古菌嗜盐嗜碱菌中，SecD和SecF组分在天然宿主中形成一种细胞质膜复合物。此外，与大肠杆菌一样，嗜盐嗜碱菌的deltasecFD突变株既表现出严重的冷敏感性，又存在Sec特异性的蛋白质转运缺陷。综上所述，尽管原核生物SecD和SecF同源物的转运机制组成不同，但这些结果表明它们之间存在显著的功能保守性。
