Nouwen N, de Kruijff B, Tommassen J
Department of Molecular Cell Biology, Institute of Biomembranes, Utrecht University, The Netherlands.
Proc Natl Acad Sci U S A. 1996 Jun 11;93(12):5953-7. doi: 10.1073/pnas.93.12.5953.
The SecY protein of Escherichia coli is an integral membrane component of the protein export apparatus. Suppressor mutations in the secY gene (prlA alleles) have been isolated that restore the secretion of precursor proteins with defective signal sequences. These mutations have never been shown to affect the translocation of wild-type precursor proteins. Here, we report that prlA suppressor mutations relieve the proton-motive force (pmf) dependency of the translocation of wild-type precursors, both in vivo and in vitro. Furthermore, the proton-motive force dependency of the translocation of a precursor with a stably folded domain in the mature region was suppressed by prlA mutations in vitro. These data show that prlA mutations cause a general relaxation of the export apparatus rather than a specific change that results in bypassing of the recognition of the signal sequence. In addition, these results are indicative for a mechanism in which the proton-motive force stimulates translocation by altering the conformation of the translocon.
大肠杆菌的SecY蛋白是蛋白质输出装置的一个整合膜成分。已分离出secY基因中的抑制突变（prlA等位基因），这些突变可恢复信号序列有缺陷的前体蛋白的分泌。这些突变从未被证明会影响野生型前体蛋白的转运。在此，我们报告prlA抑制突变在体内和体外均能减轻野生型前体转运对质子动力势（pmf）的依赖性。此外，体外实验中，成熟区域具有稳定折叠结构域的前体蛋白转运对质子动力势的依赖性被prlA突变所抑制。这些数据表明，prlA突变导致输出装置普遍松弛，而非导致绕过信号序列识别的特异性变化。此外，这些结果表明存在一种机制，其中质子动力势通过改变转运体的构象来刺激转运。
