title: Import of small Tim proteins into the mitochondrial intermembrane space.
abstract: Proteins of the intermembrane space (IMS) of mitochondria are typically synthesized without presequences. Little is known about their topogenesis. We used Tim13, a member of the 'small Tim protein' family, as model protein to investigate the mechanism of translocation into the IMS. Tim13 contains four conserved cysteine residues that bind a zinc ion as cofactor. Import of Tim13 did not depend on the membrane potential or ATP hydrolysis. Upon import into mitochondria Tim13 adopted a stably folded conformation in the IMS. Mutagenesis of the cysteine residues or pretreatment with metal chelators interfered with folding of Tim13 in vitro and impaired its import into mitochondria. Upon depletion of metal ions or modification of cysteine residues, imported Tim13 diffused back out of the IMS. We propose an import pathway in which (1) Tim13 can pass through the TOM complex into and out of the IMS in an unfolded conformation, and (2) cofactor acquisition stabilizes folding on the trans side of the outer membrane and traps Tim13 in the IMS, and drives unidirectional movement of the protein across the outer membrane of mitochondria.
authors.affiliation: Institut für Physiologische Chemie, Universität München, Butenandtstrasse 5, 81377 München, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Lutz
authors.forename: Walter
authors.initials: W
authors.lastname: Neupert
authors.forename: Johannes M
authors.initials: JM
authors.lastname: Herrmann
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003545:Cysteine / Q000737:chemistry; D008564:Membrane Potentials; D026901:Membrane Transport Proteins; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D008954:Models, Biological; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011487:Protein Conformation; D017510:Protein Folding; D011498:Protein Precursors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013438:Sulfhydryl Compounds / Q000737:chemistry; D014357:Trypsin; D015032:Zinc / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D011498:Protein Precursors; D029701:Saccharomyces cerevisiae Proteins; D013438:Sulfhydryl Compounds; C403093:TIM13 protein, S cerevisiae; C485737:TIMM13 protein, human; C118122:TIMM8A protein, human; D000255:Adenosine Triphosphate; D014357:Trypsin; D015032:Zinc; D003545:Cysteine