The Biogenesis of Mitochondrial Outer Membrane Proteins Show Variable Dependence on Import Factors

Biogenesis of mitochondrial outer membrane proteins involves their integration into the lipid bilayer. Among these proteins are those that form a single-span topology, but our understanding of their biogenesis is scarce. In this study, we found that the MIM complex is required for the membrane insertion of some single-span proteins. However, other such proteins integrate into the membrane in a MIM-independent manner. Moreover, the biogenesis of the studied proteins was dependent to a variable degree on the TOM receptors Tom20 and Tom70. We found that Atg32 C-terminal domain mediates dependency on Tom20, whereas the cytosolic domains of Atg32 and Gem1 facilitate MIM involvement. Collectively, our findings (1) enlarge the repertoire of MIM substrates to include also tail-anchored proteins, (2) provide new mechanistic insights to the functions of the MIM complex and TOM import receptors, and (3) demonstrate that the biogenesis of MOM single-span proteins shows variable dependence on import factors.