The Endoplasmic Reticulum-Mitochondria Encounter Structure Complex Coordinates Coenzyme Q Biosynthesis.

Loss of the endoplasmic reticulum (ER)-mitochondria encounter structure (ERMES) complex that resides in contact sites between the yeast ER and mitochondria leads to impaired respiration; however, the reason for that is not clear. We find that in null mutants, there is an increase in the level of mRNAs encoding for biosynthetic enzymes of coenzyme Q (CoQ), an essential electron carrier of the mitochondrial respiratory chain. We show that the mega complexes involved in CoQ biosynthesis (CoQ synthomes) are destabilized in ERMES mutants. This, in turn, affects the level and distribution of CoQ within the cell, resulting in reduced mitochondrial CoQ. We suggest that these outcomes contribute to the reduced respiration observed in ERMES mutants. Fluorescence microscopy experiments demonstrate close proximity between the CoQ synthome and ERMES, suggesting a spatial coordination. The involvement of the ER-mitochondria contact site in regulation of CoQ biogenesis highlights an additional level of communication between these two organelles.