Biochemical Characterization of a Mutationally Altered Protein Translocase: Proton Motive Force Stimulation of the Initiation Phase of Translocation
Biochemical Characterization of a Mutationally Altered Protein Translocase: Proton Motive Force Stimulation of the Initiation Phase of Translocation
复制标题
突变蛋白易位酶的生化表征：易位起始阶段的质子动力刺激
作者：
H. Mori;Koreaki Ito
SecYEG整合膜复合物和SecA ATP酶的协同作用促进蛋白质跨膜转运。secY突变（secY39）影响Arg357，一个进化上保守的和功能上重要的残基，并损害体内和体外的易位功能。在这项研究中，我们使用了“超活性”的突变形式的SecA，抑制SecY39缺陷，突变改变SecY39EG易位酶的特点。结果发现，SecY39介导的前蛋白易位表现出绝对依赖于质子动力。质子动力依赖的步骤被证明是在信号肽裂解之前。我们认为，质子动力有助于蛋白质易位的起始阶段。
ABSTRACT Protein translocation across the Escherichia coli plasma membrane is facilitated by concerted actions of the SecYEG integral membrane complex and the SecA ATPase. A secY mutation (secY39) affects Arg357, an evolutionarily conserved and functionally important residue, and impairs the translocation function in vivo and in vitro. In this study, we used the “superactive” mutant forms of SecA, which suppress the SecY39 deficiency, to characterize the mutationally altered SecY39EG translocase. It was found that SecY39-mediated preprotein translocation exhibited absolute dependence on the proton motive force. The proton motive force-dependent step proved to lie before signal peptide cleavage. We suggest that the proton motive force assists in the initiation phase of protein translocation.