Oliver D B
Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut 06459.
Mol Microbiol. 1993 Jan;7(2):159-65. doi: 10.1111/j.1365-2958.1993.tb01107.x.
Recent insight into the biochemical mechanisms of protein translocation in Escherichia coli indicates that SecA ATPase is required both for the initial binding of preproteins to the inner membrane as well as subsequent translocation across this structure. SecA appears to promote these events by direct recognition of the preprotein or preprotein-SecB complex, binding to inner-membrane anionic phospholipids, insertion into the membrane bilayer and association with the preprotein translocator, SecY/SecE. ATP binding appears to control the affinity of SecA for the various components of the system and ATP hydrolysis promotes cycling between its different biochemical states. As a component likely to catalyse a rate-determining step in protein secretion, SecA synthesis is co-ordinated with the activity of the protein export pathway. This form of negative regulation appears to rely on SecA protein binding to its mRNA and repressing translation if conditions of rapid protein secretion prevail within the cell. A precise biochemical scheme for SecA-dependent catalysis of protein export and the details of secA regulation appear to be close at hand. The evolutionary conservation of SecA protein among eubacteria as well as the general requirement for translocation ATPases in other protein secretion systems argues for a mechanistic commonality of all prokaryotic protein export pathways.
最近对大肠杆菌中蛋白质转运生化机制的深入了解表明，SecA ATP酶对于前体蛋白与内膜的初始结合以及随后穿过该结构的转运都是必需的。SecA似乎通过直接识别前体蛋白或前体蛋白-SecB复合物、与内膜阴离子磷脂结合、插入膜双层以及与前体蛋白转运体SecY/SecE结合来促进这些事件。ATP结合似乎控制SecA对系统各组分的亲和力，而ATP水解促进其不同生化状态之间的循环。作为可能催化蛋白质分泌中限速步骤的一个组分，SecA的合成与蛋白质输出途径的活性相协调。这种负调控形式似乎依赖于SecA蛋白与其mRNA结合，并在细胞内存在快速蛋白质分泌的情况下抑制翻译。SecA依赖的蛋白质分泌催化的精确生化方案以及secA调控的细节似乎即将明晰。SecA蛋白在真细菌中的进化保守性以及其他蛋白质分泌系统中对转运ATP酶的普遍需求表明，所有原核生物蛋白质输出途径在机制上具有共性。
