9.B.178 The MdmD Complementing Protein 1 (Mcp1) Family

The yeast mitochondrial outer membrane (MOM) protein Mdm10 is involved in at least three different processes: (1) association of mitochondria with the endoplasmic reticulum and mitochondrial lipid homeostasis (2) membrane assembly of MOM proteins, and (3) inheritance and morphogenesis of mitochondria. To decipher the precise role of Mdm10 in mitochondrial function, Tan et al. 2013 screened for high-copy suppressors of the severe growth defect of a mdm10Δ mutant. They identified two novel mitochondrial proteins (open reading frames YOR228c and YLR253w) that were named Mdm10 complementing protein (Mcp) 1 and Mcp2. Overexpression of Mcp1 or Mcp2 restored the alterations in morphology and stability of respiratory chain complexes of mitochondria devoid of Mdm10, but the observed defect in assembly of MOM proteins was not rescued. Lipid analyses demonstrated that elevated levels of Mcp1 and Mcp2 restore the alterations in mitochondrial phospholipid and ergosterol homeostasis in cells lacking Mdm10. Thus, two novel proteins play a role in mitochondrial lipid homeostasis A role of Mdm10 in ergosterol trafficking is suggested (Tan et al. 2013).