Nature2014-06-17 4:46 PM

来自嗜碱芽孢杆菌的YidC的结构 Structural basis of Sec-independent membrane protein insertion by YidC

论文摘要 

细菌蛋白YidC (线粒体Oxa1和叶绿体Alb3的一个同源物)不仅仅只是一个伴侣分子,与Sec机构合作来促进其膜蛋白基质的正确折叠和膜拓扑,它还独立于Sec将几个单跨或双跨膜蛋白插入到膜内。Osamu Nureki 及同事发表了等待已久的YidC结构,它让我们对这种膜蛋白的第二个作用能够有所认识。该结构显示,YidC并没有采用一个与多肽传导通道相似的架构。相反,该蛋白内一个新颖的皱褶形成一个带正电的亲水性槽。作者通过基于结构的功能分析发现,该槽中一个保守的Arg残基与一个基质蛋白的N-端区域的酸残基之间的静电相互作用,是该基质由YidC介导的向膜内的插入所必需的。

Abstract 

Newly synthesized membrane proteins must be accurately inserted into the membrane, folded and assembled for proper functioning. The protein YidC inserts its substrates into the membrane, thereby facilitating membrane protein assembly in bacteria; the homologous proteins Oxa1 and Alb3 have the same function in mitochondria and chloroplasts, respectively1, 2. In the bacterial cytoplasmic membrane, YidC functions as an independent insertase and a membrane chaperone in cooperation with the translocon SecYEG3, 4, 5. Here we present the crystal structure of YidC from Bacillus halodurans, at 2.4 Å resolution. The structure reveals a novel fold, in which five conserved transmembrane helices form a positively charged hydrophilic groove that is open towards both the lipid bilayer and the cytoplasm but closed on the extracellular side. Structure-based in vivo analyses reveal that a conserved arginine residue in the groove is important for the insertion of membrane proteins by YidC. We propose an insertion mechanism for single-spanning membrane proteins, in which the hydrophilic environment generated by the groove recruits the extracellular regions of substrates into the low-dielectric environment of the membrane.

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