Mitochondrial outer membrane channels: Emerging diversity in transport processes
Becker T, Wagner R.
Mitochondrial function and biogenesis depends on the transport of proteins, lipids, ions and metabolites across the two surrounding membranes. Various specific transporter proteins have been identified in the inner membrane. In contrast, it was thought that only a handful of beta-barrel proteins allow the passage of proteins and small molecules across the outer membrane. The voltage dependent anion channel (VDAC) forms a pore that allow the passage of metabolites and ions. Tom40 of the translocase of the mitochondrial outer membrane (TOM) and Sam50 of the sorting assembly machinery (SAM) form protein-conducting channels. Recent studies indicated that the number of channel-forming outer membrane proteins is larger than originally anticipated. In total five channel activities have been identified in outer membrane vesicles or with reconstituted outer membrane proteins. Furthermore, structural analysis reveal how protein-conducting channel can transport a large set of different proteins. In this review, we describe the emerging diversity of outer membrane transport processes.
