title: Remodelling of the active presequence translocase drives motor-dependent mitochondrial protein translocation.
abstract: Proteins with N-terminal targeting signals are transported across the inner mitochondrial membrane by the presequence translocase. To drive precursor translocation, the Hsp70-import motor associates with the protein-conducting channel of the TIM23 complex. It is unknown how the ATPase cycle of Hsp70 is regulated in the context of a translocating polypeptide chain. Here we establish an assay to monitor protein dynamics in the precursor-occupied presequence translocase and find that regulatory subunits of the import motor, such as the ATPase-stimulating J-protein Pam18, are recruited into the translocation intermediate. The presence of all Hsp70 co-chaperones at the import channel is not sufficient to promote matrix protein import, instead a recharging of the active translocase with Pam18 is required for motor activity. Thus, a replenishment cycle of co-chaperones at the TIM23 complex is an integral part of Hsp70's ATPase cycle at the channel exit site and essential to maintain motor-driven mitochondrial protein import.
authors.affiliation: Department of Cellular Biochemistry, University Medical Center Göttingen, D-37073 Göttingen, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Schulz
authors.affiliation: 1] Department of Cellular Biochemistry, University Medical Center Göttingen, D-37073 Göttingen, Germany [2] Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Rehling
mesh_terms: D000251:Adenosine Triphosphatases / Q000502:physiology; D002352:Carrier Proteins / Q000502:physiology*; D018840:HSP70 Heat-Shock Proteins / Q000502:physiology; D026901:Membrane Transport Proteins / Q000502:physiology*; D033681:Mitochondrial Membrane Transport Proteins / Q000502:physiology*; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D018832:Molecular Chaperones / Q000502:physiology; D020409:Molecular Motor Proteins / Q000502:physiology; D021381:Protein Transport / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000502:physiology*
chemical_list: D002352:Carrier Proteins; D018840:HSP70 Heat-Shock Proteins; D026901:Membrane Transport Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D018832:Molecular Chaperones; D020409:Molecular Motor Proteins; C480348:PAM18 J protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C083081:TIM23 protein, S cerevisiae; D000251:Adenosine Triphosphatases