Independent evolution of functionally exchangeable mitochondrial outer membrane import complexes

Assembly and/or insertion of a subset of mitochondrial outer membrane (MOM)
proteins, including subunits of the main MOM translocase, require the fungi-specific Mim1/Mim2
complex. So far it was unclear which proteins accomplish this task in other eukaryotes. Here, we
show by reciprocal complementation that the MOM protein pATOM36 of trypanosomes is a
functional analogue of yeast Mim1/Mim2 complex, even though these proteins show neither
sequence nor topological similarity. Expression of pATOM36 rescues almost all growth,
mitochondrial biogenesis, and morphology defects in yeast cells lacking Mim1 and/or Mim2.
Conversely, co-expression of Mim1 and Mim2 restores the assembly and/or insertion defects of
MOM proteins in trypanosomes ablated for pATOM36. Mim1/Mim2 and pATOM36 form native-like
complexes when heterologously expressed, indicating that additional proteins are not part of these
structures. Our findings indicate that Mim1/Mim2 and pATOM36 are the products of convergent
evolution and arose only after the ancestors of fungi and trypanosomatids diverged.