Molecular Mechanisms Underlying the Early Stage of Protein Translocation through the Sec Translocon
Molecular Mechanisms Underlying the Early Stage of Protein Translocation through the Sec Translocon
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DOI：
10.1021/bi901594w
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发表时间：
2010-02-09
期刊：
影响因子：
2.9
通讯作者：
Sugita, Yuji
中科院分区：
文献类型：
--
作者：
Mori, Takaharu;Ishitani, Ryuichiro;Sugita, Yuji
Sec 易位子是一种蛋白质传导通道，由异三聚体复合物（细菌中的 SecYEG 和真核生物中的 Sec61 alpha beta gamma）组成，为分泌蛋白跨膜或膜蛋白整合到膜中提供途径。 See 易位子本身是一个被动通道，蛋白质易位需要与通道伙伴（包括细菌中的核糖体或 SecA ATP 酶）结合。最近发表的三种 SecY 晶体结构被认为代表了闭合（静止状态）、预开放（通过模拟 SecA 相互作用的结合 Fab 片段确定的过渡状态）和 SecA 结合形式。为了阐明封闭形式和预开放形式之间的转变机制，我们在显式溶剂和膜中对嗜热栖热菌 SecYE 的预开放形式和詹氏甲烷球菌 SecYE beta 的封闭形式进行了全原子分子动力学模拟。我们发现 SecY 的闭合形式是稳定的，而没有 Fab 片段的预开放形式经历了向闭合形式的较大构象变化。 SecY 与 Fab 的预开放形式保持不变，表明模拟 SecA 结合的胞质相互作用稳定了 SecY 的预开放形式。重要的是，似乎需要侧门区域的脂质分子来维持膜中的预打开形式。我们提出，与 SecA 结合后，SecY 从关闭状态到预打开状态的构象转变有利于磷脂在侧门的嵌入，诱导带正电的信号肽最初进入通道。
The Sec translocon, a protein-conducting channel, consists of a heterotrimeric complex (SecYEG in bacteria and Sec61 alpha beta gamma in eukaryotes) that provides a pathway for secretary proteins to cross membranes, or for membrane proteins to integrate into the membrane. The See translocon alone is a passive channel, and association with channel partners, including the ribosome or SecA ATPase in bacteria, is needed for protein translocation. Three recently published crystal structures of SecY are considered to represent the closed (resting state), pre-open (transitional state determined with the bound Fab fragment mimicking SecA interaction), and SecA-bound forms. To elucidate mechanisms of transition between closed and pre-open forms, we performed all-atom molecular dynamics simulations for the pre-open form of Thermus thermophilus SecYE and the closed form of Methanococcus janaschii SecYE beta in explicit solvent and membranes. We found that the closed form of SecY is stable, while the pre-open form without the Fab fragment undergoes large conformational changes toward the closed form. The pre-open form of SecY with Fab remains unchanged, suggesting that the cytosolic interaction mimicking SecA binding stabilizes the pre-open form of SecY. Importantly, a lipid molecule at the lateral gate region appears to be required to maintain the pre-open form in the membrane. We propose that the conformational transition from closed to pre-open states of SecY upon association with SecA facilitates intercalation of phospholipids at the lateral gate, inducing initial entry of the positively charged signal peptide into the channel.