title: Electron cryomicroscopy structure of a membrane-anchored mitochondrial AAA protease.
abstract: FtsH-related AAA proteases are conserved membrane-anchored, ATP-dependent molecular machines, which mediate the processing and turnover of soluble and membrane-embedded proteins in eubacteria, mitochondria, and chloroplasts. Homo- and hetero-oligomeric proteolytic complexes exist, which are composed of homologous subunits harboring an ATPase domain of the AAA family and an H41 metallopeptidase domain. Mutations in subunits of mitochondrial m-AAA proteases have been associated with different neurodegenerative disorders in human, raising questions on the functional differences between homo- and hetero-oligomeric AAA proteases. Here, we have analyzed the hetero-oligomeric yeast m-AAA protease composed of homologous Yta10 and Yta12 subunits. We combined genetic and structural approaches to define the molecular determinants for oligomer assembly and to assess functional similarities between Yta10 and Yta12. We demonstrate that replacement of only two amino acid residues within the metallopeptidase domain of Yta12 allows its assembly into homo-oligomeric complexes. To provide a molecular explanation, we determined the 12 Å resolution structure of the intact yeast m-AAA protease with its transmembrane domains by electron cryomicroscopy (cryo-EM) and atomic structure fitting. The full-length m-AAA protease has a bipartite structure and is a hexamer in solution. We found that residues in Yta12, which facilitate homo-oligomerization when mutated, are located at the interface between neighboring protomers in the hexamer ring. Notably, the transmembrane and intermembrane space domains are separated from the main body, creating a passage on the matrix side, which is wide enough to accommodate unfolded but not folded polypeptides. These results suggest a mechanism regarding how proteins are recognized and degraded by m-AAA proteases.
authors.affiliation: Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Sukyeong
authors.initials: S
authors.lastname: Lee
authors.forename: Steffen
authors.initials: S
authors.lastname: Augustin
authors.forename: Takashi
authors.initials: T
authors.lastname: Tatsuta
authors.forename: Florian
authors.initials: F
authors.lastname: Gerdes
authors.forename: Thomas
authors.initials: T
authors.lastname: Langer
authors.forename: Francis T F
authors.initials: FT
authors.lastname: Tsai
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism; D000818:Animals; D020285:Cryoelectron Microscopy; D006801:Humans; D008666:Metalloendopeptidases / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000201:enzymology*; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D019636:Neurodegenerative Diseases / Q000201:enzymology / Q000235:genetics; D017510:Protein Folding; D055503:Protein Multimerization / Q000502:physiology; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D024101:Mitochondrial Proteins; D029701:Saccharomyces cerevisiae Proteins; D008666:Metalloendopeptidases; C114583:m-AAA proteases; D000251:Adenosine Triphosphatases; C102166:YTA12 protein, S cerevisiae; C090045:AFG3 protein, S cerevisiae