Mitochondrial biogenesis. Protein import into and across the inner membrane

Abstract

The mitochondrion has developed an elaborate translocation system for the import of nuclear-coded proteins and the export of proteins coded on the mitochondrial genome. Precursor proteins contain targeting and sorting information to reach the mitochondrion, while the translocons recognize the information and direct the pre-cursor to the correct compartment. The outer membrane contains the TOM (translocase of the outer membrane) complex while the inner membrane has developed a more complex system. The TIM23 (translocase of the inner membrane) mediates the import of mitochondrial proteins with a typical amino-terminal targeting sequence, and the TIM22 complex mediates the import of polytopic inner membrane proteins. Based on its prokaryotic origin, the inner membrane also contains several components that mediate the export and assembly of proteins from within the matrix. Together the export complexes and TIM translocons coordinate mitochondrial inner membrane biogenesis.