Clemons William M, Ménétret Jean-François, Akey Christopher W, Rapoport Tom A
Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA.
Curr Opin Struct Biol. 2004 Aug;14(4):390-6. doi: 10.1016/j.sbi.2004.07.006.
A structurally conserved protein translocation channel is formed by the heterotrimeric Sec61 complex in eukaryotes, and SecY complex in archaea and bacteria. Electron microscopy studies suggest that the channel may function as an oligomeric assembly of Sec61 or SecY complexes. Remarkably, the recently determined X-ray structure of an archaeal SecY complex indicates that the pore is located at the center of a single molecule of the complex. This structure suggests how the pore opens perpendicular to the plane of the membrane to allow the passage of newly synthesized secretory proteins across the membrane and opens laterally to allow transmembrane segments of nascent membrane proteins to enter the lipid bilayer. The electron microscopy and X-ray results together suggest that only one copy of the SecY or Sec61 complex within an oligomer translocates a polypeptide chain at any given time.
在真核生物中，异源三聚体Sec61复合物形成结构保守的蛋白质转运通道，而在古细菌和细菌中则由SecY复合物形成。电子显微镜研究表明，该通道可能作为Sec61或SecY复合物的寡聚体发挥作用。值得注意的是，最近确定的古细菌SecY复合物的X射线结构表明，孔位于复合物单个分子的中心。这种结构揭示了孔如何垂直于膜平面打开，以使新合成的分泌蛋白穿过膜，以及如何侧向打开，以使新生膜蛋白的跨膜片段进入脂质双层。电子显微镜和X射线结果共同表明，在任何给定时间，寡聚体内SecY或Sec61复合物的只有一个拷贝转运一条多肽链。
