The Mitochondrial Protein Import Motor
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Andreas Strub
Abstract
Mitochondrial proteins are synthesized as precursor proteins in the cytosol and are posttranslationally imported into the organelle. A complex system of translocation machineries recognizes and transports the precursor polypeptide across the mitochondrial membranes. Energy for the translocation process is mainly supplied by the mitochondrial membrane potential (∆ψ) and the hydrolysis of ATP. Mitochondrial Hsp70 (mtHsp70) has been identified as the major ATPase driving the membrane transport of the precursor polypeptides into the mitochondrial matrix. Together with the partner proteins Tim44 and Mge1, mtHsp70 forms an import motor complex interacting with the incoming preproteins at the inner face of the inner membrane. This import motor complex drives the movement of the polypeptides in the translocation channel and the unfolding of carboxy-terminal parts of the preproteins on the outside of the outer membrane. Two models of the molecular mechanism of mtHsp70 during polypeptide translocation are discussed. In the ‘trapping’ model, precursor movement is generated by Brownian movement of the polypeptide chain in the translocation pore. This random movement is made vectorial by the interaction with mtHsp70 in the matrix. The detailed characterization of conditional mutants of the import motor complex provides the basis for an extended model. In this ‘pulling’ model, the attachment of mtHsp70 at the inner membrane via Tim44 and a conformational change induced by ATP results in the generation of an inward-directed force on the bound precursor polypeptide. This active role of the import motor complex is necessary for the translocation of proteins containing tightly folded domains. We suggest that both mechanisms complement each other to reach a high efficiency of preprotein import.
Copyright © 2000 by Walter de Gruyter GmbH & Co. KG
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Articles in the same Issue
- Alexander J. Varshavsky Felix Hoppe-Seyler Lecturer 2000
- The Ubiquitin System and the N-End Rule Pathway
- Paper of the Year 1999: Award to Igor Stagljar
- A Clockwork Organ
- The Transgeneticists Toolbox: Novel Methods for the Targeted Modification of Eukaryotic Genomes
- Interdependence of Filamentous Actin and Microtubules for Asymmetric Cell Division
- Genetic Analysis of Mammalian Cyclin-Dependent Kinases and Their Inhibitors
- Phosphorylcholine Substituents in Nematodes: Structures, Occurrence and Biological Implications
- Selenium in Biology: Facts and Medical Perspectives
- The Role of Se, Mo and Fe in the Structure and Function of Carbon Monoxide Dehydrogenase
- Molecular Basis for Interactions of the DnaK Chaperone with Substrates
- Protein Import: the Hitchhikers Guide into Chloroplasts
- Pathway Analysis and Metabolic Engineering in Corynebacterium glutamicum
- Metabolic Networks: a Signal-Oriented Approach to Cellular Models
- Representing and Analysing Molecular and Cellular Function Using the Computer
- Protein Aggregation and Pathogenesis of Huntingtons Disease: Mechanisms and Correlations
- The Mitochondrial Protein Import Motor
- The Immunoglobulin κ Gene Families of Human and Mouse: a Cottage Industry Approach
- Protein-Protein Interactions in Receptor Activation and Intracellular Signalling
- Molecular Genetic Analysis of Glucocorticoid Signaling Using the Cre/loxP System
- Macromolecular Intelligence in Microorganisms
- Thyroid Hormone Receptors Bind to an Element in the Connexin43 Promoter
- Analysis of the Deubiquitinating Enzymes of the Yeast Saccharomyces cerevisiae
- Helical Tubes of FtsZ from Methanococcus jannaschii
- Surface Topography of Microtubule Walls Decorated with Monomeric and Dimeric Kinesin Constructs
- Histone Deacetylase Activity Is Required for the Induction of the MyoD Muscle Cell Lineage in Xenopus
- The Effect of Heat Shock on 20S/26S Proteasomes
- Sec61p Is the Main Ribosome Receptor in the Endoplasmic Reticulum of Saccharomyces cerevisiae
