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Timing the catch

Nature Structural & Molecular Biology volume 11, pages 6–8 (2004)Cite this article

The mitochondrial 70 kDa heat shock protein (mtHsp70) drives the import of presequence-containing polypeptides into the matrix of mitochondria. A new essential component of the import motor was discovered that regulates the ATP hydrolysis activity of mtHsp70, thereby timing its binding to the incoming polypeptide chain.

The evolutionary success of eukaryotic organisms relies on the compartmentalization of metabolic processes. The drawback of this feature is the necessity to efficiently transport the appropriate proteins into the different compartments and organelles such as the endoplasmatic reticulum (ER) and mitochondria. Approximately 1,000 different proteins are imported into mitochondria through the translocases of the outer and inner membrane, TOM, TIM22 and TIM23 (refs. 1,2). The driving force for the transport of the vast majority of them through the presequence-specific TIM23 complex is supplied by the membrane potential, Δψ, and by the ATP hydrolyzing mtHsp70, which constitutes the energy-consuming part of the import motor. In the early 1990's two other essential components of the mitochondrial import motor were discovered, the peripheral membrane protein Tim44, which interacts with mtHsp70 and the TIM23 complex, and Mge1, the nucleotide exchange factor of mtHsp70. Based on the observed interactions and activities of these proteins, two contentious models for the mechanism of the protein import were proposed, the 'Brownian ratchet' and 'power stroke' models1,3.

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Figure 1: Import of presequence-containing protein into mitochondria.

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  1. Zentrum für Molekulare Biologie, Universität Heidelberg, Im Neuenheimer Feld 282, Heidelberg, 69120, Germany

    Matthias P Mayer

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  1. Matthias P Mayer
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Mayer, M. Timing the catch. Nat Struct Mol Biol 11, 6–8 (2004). https://doi.org/10.1038/nsmb0104-6

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