title: Different import pathways through the mitochondrial intermembrane space for inner membrane proteins.
abstract: Earlier work on the protein import system of yeast mitochondria has identified two soluble 70 kDa protein complexes in the intermembrane space. One complex contains the essential proteins Tim9p and Tim10p and mediates transport of cytosolically-made metabolite carrier proteins from the outer to the inner membrane. The other complex contains the non-essential proteins Tim8p and Tim13p as well as loosely associated Tim9p; its function was unclear, but it interacted structurally or functionally with the Tim9p-Tim10p complex. We now show that the two 70 kDa complexes each mediate the import of a different subset of integral inner membrane proteins and that they can transfer these proteins to one of three different membrane insertion sites: the TIM22 complex, the TIM23 complex or an as yet uncharacterized insertion site. Yeast mitochondria thus use multiple pathways for escorting hydrophobic inner membrane proteins across the aqueous intermembrane space.
authors.affiliation: Biozentrum der Universität Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland.
authors.forename: D
authors.initials: D
authors.lastname: Leuenberger
authors.forename: N A
authors.initials: NA
authors.lastname: Bally
authors.forename: G
authors.initials: G
authors.lastname: Schatz
authors.forename: C M
authors.initials: CM
authors.lastname: Koehler
mesh_terms: D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D008954:Models, Biological; D016296:Mutagenesis; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D013696:Temperature; D013997:Time Factors
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D029701:Saccharomyces cerevisiae Proteins; C102549:TIM22 protein, S cerevisiae; C083081:TIM23 protein, S cerevisiae; C116366:Tim9 protein, S cerevisiae