Shvets Elena, Fass Ephraim, Scherz-Shouval Ruthie, Elazar Zvulun
Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel.
J Cell Sci. 2008 Aug 15;121(Pt 16):2685-95. doi: 10.1242/jcs.026005. Epub 2008 Jul 24.
LC3 belongs to a novel ubiquitin-like protein family that is involved in different intracellular trafficking processes, including autophagy. All members of this family share a unique three-dimensional structure composed of a C-terminal ubiquitin core and two N-terminal alpha-helices. Here, we focus on the specific contribution of these regions to autophagy induced by amino acid deprivation. We show that the ubiquitin core by itself is sufficient for LC3 processing through the conjugation machinery and for its consequent targeting to the autophagosomal membrane. The N-terminal region was found to be important for interaction between LC3 and p62/SQSTM1 (hereafter termed p62). This interaction is dependent on the first 10 amino acids of LC3 and on specific residues located within the ubiquitin core. Knockdown of LC3 isoforms and overexpression of LC3 mutants that fail to interact with p62 blocked the incorporation of p62 into autophagosomes. The accumulation of p62 was accompanied by elevated levels of polyubiquitylated detergent-insoluble structures. p62, however, is not required for LC3 lipidation, autophagosome formation and targeting to lysosomes. Our results support the proposal that LC3 is responsible for recruiting p62 into autophagosomes, a process mediated by phenylalanine 52, located within the ubiquitin core, and the N-terminal region of the protein.
LC3属于一个新型泛素样蛋白家族，参与包括自噬在内的不同细胞内运输过程。该家族的所有成员都具有独特的三维结构，由一个C端泛素核心和两个N端α螺旋组成。在这里，我们重点关注这些区域对氨基酸剥夺诱导的自噬的具体贡献。我们发现，泛素核心本身就足以通过缀合机制进行LC3加工，并使其随后靶向自噬体膜。发现N端区域对于LC3与p62/SQSTM1（以下简称p62）之间的相互作用很重要。这种相互作用取决于LC3的前10个氨基酸以及泛素核心内的特定残基。敲低LC3异构体以及过表达无法与p62相互作用的LC3突变体，会阻止p62掺入自噬体。p62的积累伴随着多聚泛素化去污剂不溶性结构水平的升高。然而，p62对于LC3脂化、自噬体形成以及靶向溶酶体并非必需。我们的结果支持以下观点，即LC3负责将p62招募到自噬体中，这一过程由位于泛素核心内的苯丙氨酸52以及该蛋白的N端区域介导。
