Department of Cell Biology, Harvard Medical School, Boston, MA.
Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA.
J Cell Biol. 2020 Mar 2;219(3). doi: 10.1083/jcb.201908142.
Clathrin-coated vesicles lose their clathrin lattice within seconds of pinching off, through the action of the Hsc70 "uncoating ATPase." The J- and PTEN-like domain-containing proteins, auxilin 1 (Aux1) and auxilin 2 (GAK), recruit Hsc70. The PTEN-like domain has no phosphatase activity, but it can recognize phosphatidylinositol phosphate head groups. Aux1 and GAK appear on coated vesicles in successive transient bursts, immediately after dynamin-mediated membrane scission has released the vesicle from the plasma membrane. These bursts contain a very small number of auxilins, and even four to six molecules are sufficient to mediate uncoating. In contrast, we could not detect auxilins in abortive pits or at any time during coated pit assembly. We previously showed that clathrin-coated vesicles have a dynamic phosphoinositide landscape, and we have proposed that lipid head group recognition might determine the timing of Aux1 and GAK appearance. The differential recruitment of Aux1 and GAK correlates with temporal variations in phosphoinositide composition, consistent with a lipid-switch timing mechanism.
网格蛋白包被小泡在脱离质膜的几秒钟内，通过 Hsc70“解包被 ATP 酶”的作用失去网格蛋白晶格。J 和 PTEN 样结构域包含蛋白辅助蛋白 1（Aux1）和辅助蛋白 2（GAK）募集 Hsc70。PTEN 样结构域没有磷酸酶活性，但它可以识别磷酸肌醇磷酸头部基团。Aux1 和 GAK 在动力蛋白介导的膜断裂后，立即在覆盖的小泡上连续短暂爆发，从小泡从质膜上释放出来。这些爆发包含非常少量的辅助蛋白，即使是四到六个分子也足以介导解包被。相比之下，我们在中止凹坑或在包被小窝组装的任何时间都无法检测到辅助蛋白。我们之前表明，网格蛋白包被小泡具有动态的磷酯酰肌醇景观，我们提出脂质头部基团识别可能决定 Aux1 和 GAK 出现的时间。Aux1 和 GAK 的差异募集与磷酯酰肌醇组成的时间变化相关，与脂质开关时间机制一致。
