Economou A, Wickner W
Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755-3844.
Cell. 1994 Sep 9;78(5):835-43. doi: 10.1016/s0092-8674(94)90582-7.
SecA, the peripheral subunit of E. coli preprotein translocase, alternates between a membrane inserted and a deinserted state as part of the catalytic cycle of preprotein translocation. When SecA is complexed with SecY/E and preprotein, ATP drives a profound conformational change, leading to membrane insertion of a 30 kDa domain of SecA. The inserted domain is protease-inaccessible from the cytosolic side of the membrane, but becomes accessible upon membrane disruption. Concomitant with 30 kDa domain insertion, approximately 20 aminoacyl residues of the preprotein are translocated. Additional ATP, which may be hydrolyzed at the second ATP site of SecA, releases the translocated preprotein and allows the 30 kDa domain to deinsert, whence it can exchange with cytosolic SecA. Thus, SecA is the mobile subunit of an integral membrane transporter, consuming ATP during both the insertion and deinsertion phases of its catalytic cycle while guiding preprotein segments across the membrane.
SecA是大肠杆菌前体蛋白转位酶的外周亚基，作为前体蛋白转位催化循环的一部分，它在插入膜和从膜上脱嵌的状态之间交替变化。当SecA与SecY/E和前体蛋白形成复合物时，ATP驱动其发生深刻的构象变化，导致SecA的一个30 kDa结构域插入膜中。从膜的胞质侧来看，插入的结构域对蛋白酶是不可接近的，但在膜破裂时会变得可接近。伴随30 kDa结构域的插入，前体蛋白约20个氨酰基残基发生转位。额外的ATP（可能在SecA的第二个ATP位点水解）释放已转位的前体蛋白，并使30 kDa结构域脱嵌，之后它可以与胞质中的SecA进行交换。因此，SecA是一种整合膜转运体的可移动亚基，在其催化循环的插入和脱嵌阶段都消耗ATP，同时引导前体蛋白片段穿过膜。
