heat shock protein;
Mge1;
mitochondria;
mtHsp70;
protein import;
Tim44;
D O I:
10.1515/BC.2000.115
中图分类号:
Q5 [生物化学];
Q7 [分子生物学];
学科分类号:
071010 ;
081704 ;
摘要:
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 (Delta psi) 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.
机构:
MEM SLOAN KETTERING CANC CTR, CELLULAR BIOCHEM & BIOPHYS PROGRAM, NEW YORK, NY 10021 USAMEM SLOAN KETTERING CANC CTR, CELLULAR BIOCHEM & BIOPHYS PROGRAM, NEW YORK, NY 10021 USA
机构:
MEM SLOAN KETTERING CANC CTR, CELLULAR BIOCHEM & BIOPHYS PROGRAM, NEW YORK, NY 10021 USAMEM SLOAN KETTERING CANC CTR, CELLULAR BIOCHEM & BIOPHYS PROGRAM, NEW YORK, NY 10021 USA