Mateja Agnieszka, Szlachcic Anna, Downing Maureen E, Dobosz Malgorzata, Mariappan Malaiyalam, Hegde Ramanujan S, Keenan Robert J
Department of Biochemistry & Molecular Biology, The University of Chicago, Gordon Center for Integrative Science, Room W238, 929 East 57th Street, Chicago, Illinois 60637, USA.
Nature. 2009 Sep 17;461(7262):361-6. doi: 10.1038/nature08319. Epub 2009 Aug 12.
Targeting of newly synthesized membrane proteins to the endoplasmic reticulum is an essential cellular process. Most membrane proteins are recognized and targeted co-translationally by the signal recognition particle. However, nearly 5% of membrane proteins are 'tail-anchored' by a single carboxy-terminal transmembrane domain that cannot access the co-translational pathway. Instead, tail-anchored proteins are targeted post-translationally by a conserved ATPase termed Get3. The mechanistic basis for tail-anchored protein recognition or targeting by Get3 is not known. Here we present crystal structures of yeast Get3 in 'open' (nucleotide-free) and 'closed' (ADP.AlF(4)(-)-bound) dimer states. In the closed state, the dimer interface of Get3 contains an enormous hydrophobic groove implicated by mutational analyses in tail-anchored protein binding. In the open state, Get3 undergoes a striking rearrangement that disrupts the groove and shields its hydrophobic surfaces. These data provide a molecular mechanism for nucleotide-regulated binding and release of tail-anchored proteins during their membrane targeting by Get3.
将新合成的膜蛋白靶向内质网是一个重要的细胞过程。大多数膜蛋白由信号识别颗粒共翻译识别并靶向。然而，近5%的膜蛋白通过单个羧基末端跨膜结构域“尾锚定”，该结构域无法进入共翻译途径。相反，尾锚定蛋白由一种名为Get3的保守ATP酶在翻译后靶向。Get3识别或靶向尾锚定蛋白的机制基础尚不清楚。在这里，我们展示了处于“开放”（无核苷酸）和“封闭”（结合ADP·AlF₄⁻）二聚体状态的酵母Get3的晶体结构。在封闭状态下，Get3的二聚体界面包含一个巨大的疏水凹槽，突变分析表明该凹槽与尾锚定蛋白结合有关。在开放状态下，Get3发生显著重排，破坏了凹槽并屏蔽了其疏水表面。这些数据为Get3在将尾锚定蛋白靶向膜的过程中核苷酸调节的结合和释放提供了分子机制。
