title: Role of ATP in mitochondrial protein import. Conformational alteration of a precursor protein can substitute for ATP requirement.
abstract: The role of nucleoside triphosphates (NTPs) in the import of porin into the mitochondrial outer membrane was investigated with two forms of the porin precursor: the in vitro synthesized biosynthetic precursor (bs-porin) and a water-soluble form of porin (ws-porin) obtained by subjecting the membrane-derived porin to an acid-base treatment (exposure to trichloroacetic acid, followed by alkali and rapid neutralization). The import of ws-porin into mitochondria did not require NTPs, whereas the import of bs-porin required NTPs. In other characteristics, such as binding to a specific receptor protein on the mitochondrial surface, two-step insertion into the outer membrane, and formation of specific membrane channels, ws-porin was indistinguishable from bs-porin. Thus, the acid-base treatment applied in the preparation of ws-porin can substitute for the NTP-requiring step in mitochondrial protein import. We conclude that NTPs are required for unfolding mitochondrial precursor proteins ("translocation competent folding").
authors.affiliation: Institut für Physiologische Chemie, Universität München, Federal Republic of Germany.
authors.forename: N
authors.initials: N
authors.lastname: Pfanner
authors.forename: R
authors.initials: R
authors.lastname: Pfaller
authors.forename: R
authors.initials: R
authors.lastname: Kleene
authors.forename: M
authors.initials: M
authors.lastname: Ito
authors.forename: M
authors.initials: M
authors.lastname: Tropschug
authors.forename: W
authors.initials: W
authors.lastname: Neupert
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001081:Apyrase / Q000378:metabolism; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D001693:Biological Transport, Active; D008565:Membrane Proteins / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D000226:Mitochondrial ADP, ATP Translocases / Q000378:metabolism; D009492:Neurospora crassa; D018272:Porins; D011487:Protein Conformation; D011498:Protein Precursors / Q000378:metabolism*; D011817:Rabbits
chemical_list: D001425:Bacterial Outer Membrane Proteins; D008565:Membrane Proteins; D018272:Porins; D011498:Protein Precursors; D000255:Adenosine Triphosphate; D000226:Mitochondrial ADP, ATP Translocases; D001081:Apyrase