title: Distinct forms of mitochondrial TOM-TIM supercomplexes define signal-dependent states of preprotein sorting.
abstract: Mitochondrial import of cleavable preproteins occurs at translocation contact sites, where the translocase of the outer membrane (TOM) associates with the presequence translocase of the inner membrane (TIM23) in a supercomplex. Different views exist on the mechanism of how TIM23 mediates preprotein sorting to either the matrix or inner membrane. On the one hand, two TIM23 forms were proposed, a matrix transport form containing the presequence translocase-associated motor (PAM; TIM23-PAM) and a sorting form containing Tim21 (TIM23(SORT)). On the other hand, it was reported that TIM23 and PAM are permanently associated in a single-entity translocase. We have accumulated distinct transport intermediates of preproteins to analyze the translocases in their active, preprotein-carrying state. We identified two different forms of active TOM-TIM23 supercomplexes, TOM-TIM23(SORT) and TOM-TIM23-PAM. These two supercomplexes do not represent separate pathways but are in dynamic exchange during preprotein translocation and sorting. Depending on the signals of the preproteins, switches between the different forms of supercomplex and TIM23 are required for the completion of preprotein import.
authors.affiliation: Institut für Biochemie und Molekularbiologie, ZBMZ, Stefan-Meier-Strasse 17, 79104 Freiburg, Germany.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Chacinska
authors.forename: Martin
authors.initials: M
authors.lastname: van der Laan
authors.forename: Carola S
authors.initials: CS
authors.lastname: Mehnert
authors.forename: Bernard
authors.initials: B
authors.lastname: Guiard
authors.forename: David U
authors.initials: DU
authors.lastname: Mick
authors.forename: Dana P
authors.initials: DP
authors.lastname: Hutu
authors.forename: Kaye N
authors.initials: KN
authors.lastname: Truscott
authors.forename: Nils
authors.initials: N
authors.lastname: Wiedemann
authors.forename: Chris
authors.initials: C
authors.lastname: Meisinger
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Pfanner
authors.forename: Peter
authors.initials: P
authors.lastname: Rehling
mesh_terms: D002352:Carrier Proteins / Q000502:physiology*; D026901:Membrane Transport Proteins / Q000502:physiology*; D008928:Mitochondria / Q000378:metabolism; D033681:Mitochondrial Membrane Transport Proteins / Q000378:metabolism; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins / Q000502:physiology*; D046912:Multiprotein Complexes; D021382:Protein Sorting Signals; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism / Q000502:physiology*; D013762:Tetrahydrofolate Dehydrogenase / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D046912:Multiprotein Complexes; D021382:Protein Sorting Signals; D029701:Saccharomyces cerevisiae Proteins; C083081:TIM23 protein, S cerevisiae; C500397:Tim21 protein, S cerevisiae; D013762:Tetrahydrofolate Dehydrogenase