Mechanistic insights into fungal mitochondrial outer membrane protein biogenesis.

The majority of mitochondrial proteins are nuclear-encoded and need to be transported into the mitochondria, including the proteins in the outer mitochondrial membrane. For β-barrel proteins, the preproteins are initially recognized and imported by the TOM complex, then shuttled to the SAM complex via small Tim proteins. For ⍺-helical proteins, some preproteins are recognized by the TOM complex and imported into the membrane by the MIM complex.

Building Better Barrels - β-barrel Biogenesis and Insertion in Bacteria and Mitochondria.

β-barrel proteins are folded and inserted into outer membranes by multi-subunit protein complexes that are conserved across different types of outer membranes. In Gram-negative bacteria this complex is the barrel-assembly machinery (BAM), in mitochondria it is the sorting and assembly machinery (SAM) complex, and in chloroplasts it is the outer envelope protein Oep80. Mitochondrial β-barrel precursor proteins are translocated from the cytoplasm to the intermembrane space by the translocase of the outer membrane (TOM) complex, and stabilized by molecular chaperones before interaction with the assembly machinery.

Structural insight into mitochondrial β-barrel outer membrane protein biogenesis.

In mitochondria, β-barrel outer membrane proteins mediate protein import, metabolite transport, lipid transport, and biogenesis. The Sorting and Assembly Machinery (SAM) complex consists of three proteins that assemble as a 1:1:1 complex to fold β-barrel proteins and insert them into the mitochondrial outer membrane. We report cryoEM structures of the SAM complex from Myceliophthora thermophila, which show that Sam50 forms a 16-stranded transmembrane β-barrel with a single polypeptide-transport-associated (POTRA) domain extending into the intermembrane space.

Cloning and Multi-Subunit Expression of Mitochondrial Membrane Protein Complexes in Saccharomyces cerevisiae.

Saccharomyces cerevisiae is a useful eukaryotic expression system for mitochondrial membrane proteins due to its ease of growth and ability to provide a native membrane environment. The development of the pBEVY vector system has further increased the potential of S. cerevisiae as an expression system by creating a method for expressing multiple proteins simultaneously.