Regulated Cycling of Mitochondrial Hsp70 at the Protein Import Channel

Author:

Liu Qinglian12,D'Silva Patrick1,Walter William1,Marszalek Jaroslaw1,Craig Elizabeth A.1

Affiliation:

1. Department of Biochemistry,

2. Graduate Program in Biomolecular Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.

Abstract

Hsp70 of the mitochondrial matrix (mtHsp70) provides a critical driving force for the import of proteins into mitochondria. Tim44, a peripheral inner-membrane protein, tethers it to the import channel. Here, regulated interactions were found to maximize occupancy of the active, adenosine 5′-triphosphate (ATP)–bound mtHsp70 at the channel through its intrinsic high affinity for Tim44, as well as through release of adenosine diphosphate (ADP)–bound mtHsp70 from Tim44 by the cofactor Mge1. A model peptide substrate rapidly released mtHsp70 from Tim44, even in the absence of ATP hydrolysis. In vivo, the analogous interaction of translocating polypeptide would release mtHsp70 from the channel. Consistent with the ratchet model of translocation, subsequent hydrolysis of ATP would trap the polypeptide, driving import by preventing its movement back toward the cytosol.

Publisher

American Association for the Advancement of Science (AAAS)

Subject

Multidisciplinary

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