Skach William R
Department of Biochemistry and Molecular Biology, Oregon Health & Sciences University, Portland, OR 97239, USA.
J Cell Biol. 2007 Dec 31;179(7):1333-5. doi: 10.1083/jcb.200711107.
Eukaryotic polytopic membrane proteins are cotranslationally inserted into the ER membrane by a multisubunit protein-conducting channel called the Sec61 translocon. Although most major translocon components have been identified and reconstituted, their stoichiometry and functional organization remain unknown. This has led to speculative and sometimes conflicting models describing how multiple transmembrane (TM) segments might be oriented and integrated during nascent polytopic protein biogenesis. Kida et al. (see p. 1441 of this issue) shed new insight into this area by demonstrating that functional translocons exhibit a remarkable flexibility by simultaneously accommodating at least two hydrophilic translocating peptides that are separated by multiple hydrophobic TMs. These surprising findings support an expanded role for the translocon in membrane protein biogenesis and require reassessment of current views based on a single small functional pore.
真核生物多跨膜蛋白通过一种称为Sec61易位子的多亚基蛋白质传导通道共翻译插入内质网（ER）膜中。尽管大多数主要的易位子成分已被鉴定和重组，但其化学计量和功能组织仍不清楚。这导致了一些推测性的、有时相互矛盾的模型，这些模型描述了在新生多跨膜蛋白生物合成过程中多个跨膜（TM）片段可能如何定向和整合。木田等人（见本期第1441页）通过证明功能性易位子通过同时容纳至少两个被多个疏水TM隔开的亲水性转运肽而表现出显著的灵活性，为该领域提供了新的见解。这些惊人的发现支持了易位子在膜蛋白生物合成中的扩展作用，并要求重新评估基于单个小功能孔的当前观点。
