The mechanism of membrane-associated steps in tail-anchored protein insertion

摘要

Tall-anchored (TA) membrane proteins destined for the endoplasmic reticulum are chaperoned by cytosolic targeting factors that deliver them to a membrane receptor for insertion. Although a basic framework for TA protein recognition is now emerging, the decisive targeting and membrane insertion steps are not understood. Here we reconstitute the TA protein insertion cycle with purified components, present crystal structures of key complexes between these components and perform mutational analyses based on the structures. We show that a committed targeting complex, formed by a TA protein bound to the chaperone ATPase Get3, is initially recruited to the membrane through an interaction with Get2. Once the targeting complex has been recruited, Getl interacts with Get3 to drive TA protein release in an ATPase-dependent reaction. After releasing its TA protein cargo, the now-vacant Get3 recycles back to the cytosol concomitant with ATP binding. This work provides a detailed structural and mechanistic framework for the minimal TA protein insertion cycle.%大约5％的真核膜蛋白(被称为尾部固定的蛋白或TA蛋白)被一个“C-端跨膜域”固定到类脂双层上。"Get3 ATP酶”以那些以内质网(ER)为目的地的TA蛋白为目标，而“基质-Get3复合物”则与ER中被称为Getl和Get2的两个膜蛋白结合存起。