An Msp1-containing complex removes orphaned proteins in the mitochondrial outer membrane of trypanosomes (SILAC-IP data)

The AAA-ATPase Msp1 extracts mislocalized outer membrane proteins and thus contributes to mitochondrial proteostasis. Using pull down experiments, we show that trypanosomal Msp1 localizes to both the glycosome and the mitochondrial outer membrane, where it forms a stable complex with four outer membrane proteins. The trypanosome-specific pATOM36 mediates complex assembly of alpha-helically anchored mitochondrial outer membrane proteins, such as protein translocase subunits. Inhibition of complex assembly triggers a pathway that results in the proteasomal digestion of unassembled substrates. Using inducible single, double and triple RNAi cell lines combined with proteomic analyses, we demonstrate that both TbMsp1 and the trypanosomal homolog of a cytosolic AAA-ATPase, VCP, are implicated in this quality control pathway. Moreover, in the absence of TbVCP, three out of the four TbMsp1-interacting mitochondrial proteins are required for efficient proteasomal digestion of pATOM36 substrates, suggesting they act in concert with TbMsp1. pATOM36 is a functional analogue of the yeast MIM complex, and possibly of human MTCH2, suggesting that similar mitochondrial quality control pathways linked to Msp1 might also exist in yeast and humans.