Published online 31 October 2005. doi:10.1083/jcb.200507147
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 171, Number 3, 419-423
How does the TOM complex mediate insertion of precursor proteins into the mitochondrial outer membrane?
Doron Rapaport
Institute for Physiological Chemistry, Ludwig-Maximilians University, 81377 Munich, Germany
Correspondence to Doron Rapaport: rapaport{at}med.uni-muenchen.de
Abstract
A multisubunit translocase of the outer mitochondrial membrane (TOM complex) mediates both the import of mitochondrial precursor proteins into the internal compartments of the organelle and the insertion of proteins residing in the mitochondrial outer membrane. The proposed ß-barrel structure of Tom40, the pore-forming component of the translocase, raises the question of how the apparent uninterrupted ß-barrel topology can be compatible with a role of Tom40 in releasing membrane proteins into the lipid core of the bilayer. In this review, I discuss insertion mechanisms of proteins into the outer membrane and present alternative models based on the opening of a multisubunit ß-barrel TOM structure or on the interaction of outer membrane precursors with the outer face of the Tom40 ß-barrel structure.
Abbreviations used in this paper: 3D, three dimensional; TOM, translocase of outer mitochondrial membrane; TM, transmembrane.

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