Suzuki Sho W, Yamamoto Hayashi, Oikawa Yu, Kondo-Kakuta Chika, Kimura Yayoi, Hirano Hisashi, Ohsumi Yoshinori
Frontier Research Center and Department of Biological Information, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama 226-8501, Japan; and.
Frontier Research Center and
Proc Natl Acad Sci U S A. 2015 Mar 17;112(11):3350-5. doi: 10.1073/pnas.1421092112. Epub 2015 Mar 3.
During autophagosome formation, autophagosome-related (Atg) proteins are recruited hierarchically to organize the preautophagosomal structure (PAS). Atg13, which plays a central role in the initial step of PAS formation, consists of two structural regions, the N-terminal HORMA (from Hop1, Rev7, and Mad2) domain and the C-terminal disordered region. The C-terminal disordered region of Atg13, which contains the binding sites for Atg1 and Atg17, is essential for the initiation step in which the Atg1 complex is formed to serve as a scaffold for the PAS. The N-terminal HORMA domain of Atg13 is also essential for autophagy, but its molecular function has not been established. In this study, we searched for interaction partners of the Atg13 HORMA domain and found that it binds Atg9, a multispanning membrane protein that exists on specific cytoplasmic vesicles (Atg9 vesicles). After the Atg1 complex is formed, Atg9 vesicles are recruited to the PAS and become part of the autophagosomal membrane. HORMA domain mutants, which are unable to interact with Atg9, impaired the PAS localization of Atg9 vesicles and exhibited severe defects in starvation-induced autophagy. Thus, Atg9 vesicles are recruited to the PAS via the interaction with the Atg13 HORMA domain. Based on these findings, we propose that the two distinct regions of Atg13 play crucial roles in distinct steps of autophagosome formation: In the first step, Atg13 forms a scaffold for the PAS via its C-terminal disordered region, and subsequently it recruits Atg9 vesicles via its N-terminal HORMA domain.
在自噬体形成过程中，自噬体相关（Atg）蛋白按层次被招募以构建前自噬体结构（PAS）。Atg13在PAS形成的起始步骤中起核心作用，它由两个结构区域组成，即N端的HORMA（来自Hop1、Rev7和Mad2）结构域和C端的无序区域。Atg13的C端无序区域包含与Atg1和Atg17的结合位点，对于Atg1复合物形成以作为PAS支架的起始步骤至关重要。Atg13的N端HORMA结构域对于自噬也必不可少，但其分子功能尚未明确。在本研究中，我们寻找了Atg13 HORMA结构域的相互作用伙伴，发现它与Atg9结合，Atg9是一种存在于特定细胞质囊泡（Atg9囊泡）上的多次跨膜蛋白。Atg1复合物形成后，Atg9囊泡被招募到PAS并成为自噬体膜的一部分。无法与Atg9相互作用的HORMA结构域突变体损害了Atg9囊泡在PAS的定位，并在饥饿诱导的自噬中表现出严重缺陷。因此，Atg9囊泡通过与Atg13 HORMA结构域的相互作用被招募到PAS。基于这些发现，我们提出Atg13的两个不同区域在自噬体形成的不同步骤中发挥关键作用：第一步，Atg13通过其C端无序区域为PAS形成支架，随后通过其N端HORMA结构域招募Atg9囊泡。
