title: Machinery for protein sorting and assembly in the mitochondrial outer membrane.
abstract: Mitochondria contain translocases for the transport of precursor proteins across their outer and inner membranes. It has been assumed that the translocases also mediate the sorting of proteins to their submitochondrial destination. Here we show that the mitochondrial outer membrane contains a separate sorting and assembly machinery (SAM) that operates after the translocase of the outer membrane (TOM). Mas37 forms a constituent of the SAM complex. The central role of the SAM complex in the sorting and assembly pathway of outer membrane proteins explains the various pleiotropic functions that have been ascribed to Mas37 (refs 4, 11-15). These results suggest that the TOM complex, which can transport all kinds of mitochondrial precursor proteins, is not sufficient for the correct integration of outer membrane proteins with a complicated topology, and instead transfers precursor proteins to the SAM complex.
authors.affiliation: Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder-Str. 7, D-79104 Freiburg, Germany.
authors.forename: Nils
authors.initials: N
authors.lastname: Wiedemann
authors.forename: Vera
authors.initials: V
authors.lastname: Kozjak
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Chacinska
authors.forename: Birgit
authors.initials: B
authors.lastname: Schönfisch
authors.forename: Sabine
authors.initials: S
authors.lastname: Rospert
authors.forename: Michael T
authors.initials: MT
authors.lastname: Ryan
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Pfanner
authors.forename: Chris
authors.initials: C
authors.lastname: Meisinger
mesh_terms: D017353:Gene Deletion; D007425:Intracellular Membranes / Q000378:metabolism*; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D011498:Protein Precursors / Q000378:metabolism; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism
chemical_list: D046911:Macromolecular Substances; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D011498:Protein Precursors; C092812:SAM37 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C066555:Tom40 protein, S cerevisiae