Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
J Cell Biol. 2012 Dec 10;199(6):907-18. doi: 10.1083/jcb.201207163.
A critical event in protein translocation across the endoplasmic reticulum is the structural transition between the closed and open conformations of Sec61, the eukaryotic translocation channel. Channel opening allows signal sequence insertion into a gap between the N- and C-terminal halves of Sec61. We have identified a gating motif that regulates the transition between the closed and open channel conformations. Polar amino acid substitutions in the gating motif cause a gain-of-function phenotype that permits translocation of precursors with marginally hydrophobic signal sequences. In contrast, hydrophobic substitutions at certain residues in the gating motif cause a protein translocation defect. We conclude that the gating motif establishes the hydrophobicity threshold for functional insertion of a signal sequence into the Sec61 complex, thereby allowing the wild-type translocation channel to discriminate between authentic signal sequences and the less hydrophobic amino acid segments in cytosolic proteins. Bioinformatic analysis indicates that the gating motif is conserved between eubacterial and archaebacterial SecY and eukaryotic Sec61.
蛋白质跨内质网易位的一个关键事件是 Sec61（真核易位通道）构象从关闭到开放的结构转变。通道打开允许信号序列插入 Sec61 的 N 端和 C 端半体之间的间隙中。我们已经确定了一个门控基序，它调节关闭和开放通道构象之间的转变。门控基序中的极性氨基酸取代导致获得功能表型，允许具有边缘疏水性信号序列的前体易位。相比之下，门控基序中某些残基的疏水性取代会导致蛋白质易位缺陷。我们的结论是，门控基序为信号序列功能性插入 Sec61 复合物建立了疏水性阈值，从而使野生型易位通道能够区分真实的信号序列和胞质蛋白中疏水性较低的氨基酸片段。生物信息学分析表明，门控基序在真细菌和古细菌 SecY 以及真核 Sec61 之间是保守的。
