Shaping the import system of mitochondria

Abstract

Evidence is accumulating that unrelated species have independently evolved the same way of importing proteins in their mitochondria.

Keywords: MIM complex; S. cerevisiae; TOM complex; biochemistry; chemical biology; convergent evolution; mitochondria; outer membrane; trypanosome.

Figure 1.. Protein import complexes in mitochondria.

The outer mitochondrial membrane (OM) contains embedded protein complexes – such as the SAM, TOM and MIM complexes – that import proteins from the cytosol into the mitochondria. The SAM and TOM complexes interact to import β-barrel proteins (left). Certain subunits in the complexes (Tom22, Tom40 and Sam50) are highly conserved in all eukaryotes. However, the MIM complex, which imports α-helix proteins (right), is only present in fungi. Vitali et al. now show that pATOM36, an import protein found in the trypanosome T. brucei, and the MIM complex are functionally equivalent, despite their sequences being very different. This presents an exciting case of convergent evolution in a core protein import machinery of mitochondria. TOM: translocase complex of the outer membrane; SAM: sorting and assembly machinery; MIM: mitochondrial import machinery.