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Protein Science (2007), 16:316-322. Published by Cold Spring Harbor Laboratory Press. Copyright © 2007 The Protein Society
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The Pam18/Tim14–Pam16/Tim16 complex of the mitochondrial translocation motor: The formation of a stable complex from marginally stable proteins

Ohad Iosefson, Ran Levy, Milit Marom, Olga Slutsky-Leiderman, and Abdussalam Azem

Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69778, Israel

(RECEIVED July 24, 2006; FINAL REVISION October 17, 2006; ACCEPTED November 19, 2006)

The vast majority of mitochondrial proteins are imported from the cytosol. For matrix-localized proteins, the final step of translocation across the inner membrane is mediated by the mitochondrial translocation motor, of which mhsp70 is a key component. The ATP-dependent function of mhsp70 is regulated by a complex, composed of a J-protein (called Pam18 or Tim14) and a J-like protein (called Pam16 or Tim16), and the nucleotide exchange factor Mge1. In this study, we investigated the structural properties of a recombinant purified Pam18/Tim14–Pam16/Tim16 complex using cross-linking with the bifunctional reagent DSS and CD-spectroscopy. The results of the study show that both Pam18/Tim14 and Pam16/Tim16 are thermally unstable proteins that unfold at very low temperatures (Tm values of 16.5°C and 29°C, respectively). Upon mixing the proteins in vitro, or when both proteins are co-overexpressed in bacteria, Pam18/Tim14 and Pam16/Tim16 form a heterodimer that is thermally more stable than the individual proteins (Tm = 41°C). Analysis of the properties of the complex in GdnHCl shows that dissociation of the heterodimer is the limiting step in achieving full denaturation.

Keywords: mitochondrial import; translocation motor; Pam18/Tim14; Pam16/Tim16


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O. Slutsky-Leiderman, M. Marom, O. Iosefson, R. Levy, S. Maoz, and A. Azem
The Interplay between Components of the Mitochondrial Protein Translocation Motor Studied Using Purified Components
J. Biol. Chem., November 23, 2007; 282(47): 33935 - 33942.
[Abstract] [Full Text] [PDF]


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