title: Crystal structures of mitochondrial processing peptidase reveal the mode for specific cleavage of import signal sequences.
abstract: BACKGROUND
  Mitochondrial processing peptidase (MPP) is a metalloendopeptidase that cleaves the N-terminal signal sequences of nuclear-encoded proteins targeted for transport from the cytosol to the mitochondria. Mitochondrial signal sequences vary in length and sequence, but each is cleaved at a single specific site by MPP. The cleavage sites typically contain an arginine at position -2 (in the N-terminal portion) from the scissile peptide bond in addition to other distal basic residues, and an aromatic residue at position +1. Mitochondrial import machinery recognizes amphiphilic helical conformations in signal sequences. However, it is unclear how MPP specifically recognizes diverse presequence substrates.
  
  
  RESULTS
  The crystal structures of recombinant yeast MPP and a cleavage-deficient mutant of MPP complexed with synthetic signal peptides have been determined. MPP is a heterodimer; its alpha and beta subunits are homologous to the core II and core I proteins, respectively, of the ubiquinol-cytochrome c oxidoreductase complex. Crystal structures of two different synthetic substrate peptides cocrystallized with the mutant MPP each show the peptide bound in an extended conformation at the active site. Recognition sites for the arginine at position -2 and the +1 aromatic residue are observed.
  
  
  CONCLUSIONS
  MPP bound two mitochondrial import presequence peptides in extended conformations in a large polar cavity. The presequence conformations differ from the amphiphilic helical conformation recognized by mitochondrial import components. Our findings suggest that the presequences adopt context-dependent conformations through mitochondrial import and processing, helical for recognition by mitochondrial import machinery and extended for cleavage by the main processing component.
authors.affiliation: Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
authors.forename: A B
authors.initials: AB
authors.lastname: Taylor
authors.forename: B S
authors.initials: BS
authors.lastname: Smith
authors.forename: S
authors.initials: S
authors.lastname: Kitada
authors.forename: K
authors.initials: K
authors.lastname: Kojima
authors.forename: H
authors.initials: H
authors.lastname: Miyaura
authors.forename: Z
authors.initials: Z
authors.lastname: Otwinowski
authors.forename: A
authors.initials: A
authors.lastname: Ito
authors.forename: J
authors.initials: J
authors.lastname: Deisenhofer
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D014450:Electron Transport Complex III / Q000737:chemistry / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000235:genetics / Q000378:metabolism; D008291:Malate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008666:Metalloendopeptidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D010455:Peptides / Q000138:chemical synthesis / Q000378:metabolism; D011487:Protein Conformation; D021382:Protein Sorting Signals; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D000096122:Mitochondrial Processing Peptidase
chemical_list: D014450:Electron Transport Complex III; D003576:Electron Transport Complex IV; D008291:Malate Dehydrogenase; D008565:Membrane Proteins; D008666:Metalloendopeptidases; D010455:Peptides; D021382:Protein Sorting Signals; D011994:Recombinant Proteins; D000096122:Mitochondrial Processing Peptidase