title: On the mechanism of preprotein import by the mitochondrial presequence translocase.
abstract: Mitochondria are organelles of endosymbiontic origin that contain more than one thousand different proteins. The vast majority of these proteins is synthesized in the cytosol and imported into one of four mitochondrial subcompartments: outer membrane, intermembrane space, inner membrane and matrix. Several import pathways exist and are committed to different classes of precursor proteins. The presequence translocase of the inner mitochondrial membrane (TIM23 complex) mediates import of precursor proteins with cleavable amino-terminal presequences. Presequences direct precursors across the inner membrane. The combination of this presequence with adjacent regions determines if a precursor is fully translocated into the matrix or laterally sorted into the inner mitochondrial membrane. The membrane-embedded TIM23(SORT) complex mediates the membrane potential-dependent membrane insertion of precursor proteins with a stop-transfer sequence downstream of the mitochondrial targeting signal. In contrast, translocation of precursor proteins into the matrix requires the recruitment of the presequence translocase-associated motor (PAM) to the TIM23 complex. This ATP-driven import motor consists of mitochondrial Hsp70 and several membrane-associated co-chaperones. These two structurally and functionally distinct forms of the TIM23 complex (TIM23(SORT) and TIM23(MOTOR)) are in a dynamic equilibrium with each other. In this review, we discuss recent advances in our understanding of the mechanisms of matrix translocation and membrane insertion by the TIM23 machinery.
authors.affiliation: Institut für Biochemie und Molekularbiologie, Universität Freiburg, D-79104 Freiburg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: van der Laan
authors.forename: Dana P
authors.initials: DP
authors.lastname: Hutu
authors.forename: Peter
authors.initials: P
authors.lastname: Rehling
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D008564:Membrane Potentials; D026901:Membrane Transport Proteins / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology* / Q000378:metabolism; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D008954:Models, Biological; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D002352:Carrier Proteins; D018840:HSP70 Heat-Shock Proteins; D026901:Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D029701:Saccharomyces cerevisiae Proteins; C083081:TIM23 protein, S cerevisiae; D000255:Adenosine Triphosphate