title: Genetic and structural characterization of the human mitochondrial inner membrane translocase.
abstract: Translocation of nuclear-encoded mitochondrial preproteins is mediated by translocases in the outer and inner membranes. In the yeast Saccharomyces cerevisiae, translocation of preproteins into the matrix requires the membrane proteins Tim23, Tim17 and Tim44, which drive translocation in cooperation with mtHsp70 and its co-chaperone Mge1p. We have cloned and functionally analyzed the human homologues of Tim17, Tim23 and Tim44. In contrast to yeast, two TIM17 genes were found to be expressed in humans. TIM44, TIM23 and TIM17a genes were mapped to chromosomes 19p13.2-p13.3, 10q11. 21-q11.23 and 1q32. The TIM17b gene mapped to Xp11.23, near the fusion point where an autosomal region was proposed to have been added to the "ancient" part of the X chromosome about 80-130 MY ago. The primary sequences of the two proteins, hTim17a and hTim17b, are essentially identical, significant differences being restricted to their C termini. They are ubiquitously expressed in fetal and adult tissues, and both show expression levels comparable to that of hTim23. Biochemical characterization of the human Tim components revealed that hTim44 is localized in the matrix and, in contrast to yeast, only loosely associated with the inner membrane. hTim23 is organized into two distinct complexes in the inner membrane, one containing hTim17a and one containing hTim17b. Both TIM complexes display a native molecular mass of 110 kDa. We suggest that the structural organization of TIM23.17 preprotein translocases is conserved from low to high eukaryotes.
authors.affiliation: Institut für Klinische Chemie Molekularbiologische Diagnostik und Mitochondriale Genetik und Institut für Diabetesforschung, Akad, Krankenhaus München-Schwabing, Kölner Platz 1, München, D-80804, Germany. bauer@bio.med.uni-muenchen.de
authors.forename: M F
authors.initials: MF
authors.lastname: Bauer
authors.forename: K
authors.initials: K
authors.lastname: Gempel
authors.forename: A S
authors.initials: AS
authors.lastname: Reichert
authors.forename: G A
authors.initials: GA
authors.lastname: Rappold
authors.forename: P
authors.initials: P
authors.lastname: Lichtner
authors.forename: K D
authors.initials: KD
authors.lastname: Gerbitz
authors.forename: W
authors.initials: W
authors.lastname: Neupert
authors.forename: M
authors.initials: M
authors.lastname: Brunner
authors.forename: S
authors.initials: S
authors.lastname: Hofmann
mesh_terms: D000328:Adult; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics*; D002874:Chromosome Mapping; D002878:Chromosomes, Human, Pair 1; D002879:Chromosomes, Human, Pair 10; D002888:Chromosomes, Human, Pair 19; D018076:DNA, Complementary; D005333:Fetus; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics*; D026901:Membrane Transport Proteins; D051379:Mice; D000226:Mitochondrial ADP, ATP Translocases / Q000737:chemistry / Q000235:genetics*; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D009928:Organ Specificity; D051381:Rats; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry; D012097:Repressor Proteins; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014960:X Chromosome
chemical_list: D002352:Carrier Proteins; D018076:DNA, Complementary; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins; D011994:Recombinant Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; C091191:TIM17 protein, S cerevisiae; C083081:TIM23 protein, S cerevisiae; C077016:TIM44 protein, S cerevisiae; C534731:TIMM17A protein, human; C489671:TIMM44 protein, human; C489672:Timm44 protein, mouse; C489673:Timm44 protein, rat; D000226:Mitochondrial ADP, ATP Translocases