Roles of clathrin-adaptor-like proteins in intracellular protein traffic.

笼蛋白包裹的囊泡参与蛋白质从跨高尔基体网络(TGN)到溶酶体的运输和质膜受体的内吞作用。网状蛋白在TGN和质膜上的募集是由适配器蛋白(AP)复合体介导的。AP-1和AP-2复合体分别参与TGN和质膜包膜囊泡的形成。这些AP复合体由两个大的、一个中等的和一个小的亚基组成。最近，新的接头复合体AP-3和AP-4已被发现，并被证明在TGN和内小体中发挥作用。此外，我们最近发现了一个新的适配器样蛋白家族，GGA1-GGA3，其C端的EAR结构域与AP-1的γ-Adaptin亚基的结构域同源，并表明它们在TGN中发挥功能。在本研究中，我们对这些接头蛋白进行了如下研究：a)我们已经证明γ-Adaptin和GGAs的C-末端EAR结构域与γ-Synergin和Rabaptin-5结合，这两个结构域在TGN和内体中发挥作用。此外，我们还揭示了γ-Adaptin EAR结构域的X射线晶体结构，并揭示了它与γ-增效剂和Rabaptin-5.b相互作用的分子基础。b)我们发现GGAS的N-末端VMS结构域与甘露糖6-磷酸受体和山梨素细胞质结构域中的酸性簇-二亮氨酸(ACL)基序结合。此外，我们还揭示了VHS结构域与ACLL多肽之间的络合物的X射线晶体结构。c)我们利用酵母三杂交系统揭示了AP亚基之间的相互作用模式。

Clathrin-coated vesicles are involved in protein traffic from the trans-Golgi network (TGN) to lysosomes and in endocytosis of plasma membrane receptors. Recruitment of clathrin onto TGN and plasma membranes is mediated by adaptor protein (AP) complexes. The AP-1 and AP-2 complexes are involved in the formation of clathrin-coated vesicles from the TGN and plasma membrane, respectively. These AP complexes are composed of two large, one medium, and one small subunits. Recently, novel adaptor complexes, AP-3 and AP-4, have been identified and shown to function in the TGN and endosomes. Furthermore, We have recently identified a novel family of adaptor-like proteins, GGA1-GGA3, whose C-terminal ear domains are homologous to that of the, AP-1 γ-adaptin subunit, and shown that they function in the TGN. In this study, we have shown the followings on these adaptor proteins.a) We have shown that the C-terminal ear domains of γ-adaptin and GGAs bind toγ-synergin and rabaptin-5, which function in the TGN and endosomes. Furthermore, we have revealed the X-ray crystal structures of the γ-adaptin ear domain and shown the molecular basis of its interaction with γ-synergin and rabaptin-5.b) We have shown that the N-terminal VMS domain of GGAs binds to acidic cluster-dileucine (ACLL) motifs within the cytoplasmic domains of mannose 6-phosphate receptors and sortilin. Furthermore, we have revealed the X-ray crystal structure of the complex between the VHS domain and the ACLL peptide.c) We have revealed the interaction modes among the AP subunits using the yeast three-hybrid system.