Factors involved in the stop transfer process in membrane protein biogenesis

(1st我们构建了一个模型膜蛋白proOmpAl 65-LacY（TM 12）-PhoA，并分析了SecY在其整合入膜中的作用。我们发现，由于secY 125突变株中的strop转移反应效率低于野生型菌株，该模型蛋白质较不稳定地整合到膜中。另一方面，在prIA（secY）4-1突变株中，终止转移反应以增强的效率发生。这些结果有力地表明，SecY直接参与了膜蛋白生物合成中的停止转移过程。(2nd我们以前建议FtsH参与停止转移过程。结果表明：（1）FtsH与变性碱性磷酸酶有亲和力，（2）FtsH与变性碱性磷酸酶的结合不依赖于ATP，（3）FtsH不能降解结合的碱性磷酸酶。FtsH的这种变性蛋白结合活性可能在膜蛋白的生物合成，特别是停止转移过程中起一定作用。

(1st year) We constructed a model membrane protein, proOmpAl65-LacY(TM12)-PhoA, and analyzed the roles of SecY in its integration into the membrane. We found that this model protein was less stably integrated into the membrane as a result of inefficient strop transfer reaction in the secY125 mutant strain than in the wild type strain. On the other hand, the stop transfer reaction occurred with the enhanced efficiency in the prIA(secY) 4-1 mutant strain. These results strongly suggest that SecY is directly involved in the stop transfer process in biogenesis of membrane proteins.(2nd year) We suggested previously that FtsH is involved in the stop transfer process. We found that, 1) FtsH has affinity to a denatured alkaline phosphatase, 2) the binding of FtsH to a denatured alkaline phosphatase is independent of ATP, 3) FtsH is unable to degrade bound alkaline phosphatase. This denatured protein binding activity of FtsH may have some role in the biogenesis of membrane proteins, especially the stop transfer process.