Assembly of beta-barrel proteins in the mitochondrial outer membrane

摘要

Mitochondria evolved through endosymbiosis of a Gram-negative progenitor with a host cell to generate eukatyotes. Therefore, the outer membrane of mitochondria and Gram-negative bacteria contain pore proteins with beta-barrel topology. After synthesis in the cytosol, beta-barrel precursor proteins are first transported into the mitochondrial intermembrane space. Folding and membrane integration of beta-barrel proteins depend on the mitochondrial sorting and assembly machinery (SAM) located in the outer membrane, which is related to the beta-barrel assembly machinery (BAM) in bacteria. The SAM complex recognizes beta-barrel proteins by a beta-signal in the C-terminal beta-strand that is required to initiate beta-barrel protein insertion into the outer membrane. In addition, the SAM complex is crucial to form membrane contacts with the inner mitochondrial membrane by interacting with the mitochondrial contact site and cristae organizing system (MICOS) and shares a subunit with the endoplasmic reticulum-mitochondria encounter structure (ERMES) that links the outer mitochondrial membrane to the endoplasmic reticulum (ER). (C) 2014 Elsevier B.V. All rights reserved.