title: A HORMA domain in Atg13 mediates PI 3-kinase recruitment in autophagy.
abstract: Autophagy-related 13 (Atg13) is a key early-acting factor in autophagy and the major locus for nutrient-dependent regulation of autophagy by Tor. The 2.3-Å resolution crystal structure of the N-terminal domain of Atg13 reveals a previously unidentified HORMA (Hop1p, Rev1p and Mad2) domain similar to that of the spindle checkpoint protein Mad2. Mad2 has two different stable conformations, O-Mad2 and C-Mad2, and the Atg13 HORMA structure corresponds to the C-Mad2 state. The Atg13 HORMA domain is required for autophagy and for recruitment of the phosphatidylinositol (PI) 3-kinase subunit Atg14 but is not required for Atg1 interaction or Atg13 recruitment to the preautophagosomal structure. The Atg13 HORMA structure reveals a pair of conserved Arg residues that constitute a putative phosphate sensor. One of the Arg residues is in the region corresponding to the "safety belt" conformational switch of Mad2, suggesting conformational regulation of phosphate binding. These two Arg residues are essential for autophagy, suggesting that the Atg13 HORMA domain could function as a phosphoregulated conformational switch.
authors.affiliation: Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Christine C
authors.initials: CC
authors.lastname: Jao
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Ragusa
authors.forename: Robin E
authors.initials: RE
authors.lastname: Stanley
authors.forename: James H
authors.initials: JH
authors.lastname: Hurley
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry* / Q000378:metabolism*; D001343:Autophagy / Q000235:genetics*; D000071183:Autophagy-Related Proteins; D015153:Blotting, Western; D018797:Cell Cycle Proteins / Q000378:metabolism; D018360:Crystallography, X-Ray; D064246:Mad2 Proteins; D008856:Microscopy, Fluorescence; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000071183:Autophagy-Related Proteins; D018797:Cell Cycle Proteins; D064246:Mad2 Proteins; D009687:Nuclear Proteins; D019869:Phosphatidylinositol 3-Kinases; D029701:Saccharomyces cerevisiae Proteins; C413216:ATG13 protein, S cerevisiae; C577695:MAD2 protein, S cerevisiae