Coenzyme Q biosynthetic proteins assemble in a substrate-dependent manner into domains at ER–mitochondria contacts

Abstract

Coenzyme Q (CoQ) lipids are ancient electron carriers that, in eukaryotes, function in the mitochondrial respiratory chain. In mitochondria, CoQ lipids are built by an inner membrane–associated, multicomponent, biosynthetic pathway via successive steps of isoprenyl tail polymerization, 4-hydroxybenzoate head-to-tail attachment, and head modification, resulting in the production of CoQ. In yeast, we discovered that head-modifying CoQ pathway components selectively colocalize to multiple resolvable domains in vivo, representing supramolecular assemblies. In cells engineered with conditional ON or OFF CoQ pathways, domains were strictly correlated with CoQ production and substrate flux, respectively, indicating that CoQ lipid intermediates are required for domain formation. Mitochondrial CoQ domains were also observed in human cells, underscoring their conserved functional importance. CoQ domains within cells were highly enriched adjacent to ER–mitochondria contact sites. Together, our data suggest that CoQ domains function to facilitate substrate accessibility for processive and efficient CoQ production and distribution in cells.

COQ11 deletion mitigates respiratory deficiency caused by mutations in the gene encoding the coenzyme Q chaperone protein Coq10

“…(23). Two recent studies demonstrated that mitochondria isolated from yeast lacking COQ10 have a reduced number of CoQ domain puncta (23,24). This is likely due to lower levels of certain Coq polypeptides and partial CoQ synthome destabilization in the coq10Δ mutant (17,19), which was confirmed in this work ( Fig.…”

“…When Coq9-yEGFP was used as a marker for CoQ domains, coq11Δ had increased CoQ domain intensity that stemmed from amplified expression of Coq9-yEGFP, although the number of domains was similar to wild type. Mutants lacking essential Coq polypeptides coq1-coq9, or coq10, displayed significantly less Coq9-labeled domains (24). The CoQ synthome stabilization seen in coq11Δ via 2D-BN/SDS-PAGE analyses performed in this work ( Fig.…”

“…This observation has prompted speculation that Coq10 acts as a Q 6 chaperone protein required for delivery of Q 6 from its synthesis site to sites where Q 6 functions as an antioxidant and to the respiratory complexes, thereby bridging efficient de novo Q 6 biosynthesis with respiration (17). Recent studies have shown a spatial compartmentalization of the mitochondrial inner membrane with the identification of different sites, such as the inner boundary membrane, the cristae membrane, and the ER-mitochondrial contact sites (22)(23)(24)(25). Thus, for optimal respiratory competence, newly synthesized Q 6 must move from its site of synthesis (i.e.…”

“…Thus, for optimal respiratory competence, newly synthesized Q 6 must move from its site of synthesis (i.e. the ER-mitochondrial contact sites (23,24)) to the cristae membrane where the respiratory complexes are concentrated (22). The presence of Coq10-Coq11 fusions in fungal species indicates that Coq11 may have a functional association with the Coq10 chaperone to facilitate or regulate Q 6 transport for respiration in yeast.…”

Mitochondrial Enzymes of the Urea Cycle Cluster at the Inner Mitochondrial Membrane

“…While co-immunoprecipitation of the three proteins suggests stable interactions, the large difference in their abundance (Raijman 1976;Cohen, et al 1982;Sonoda and Tatibana 1983;Wang, et al 2019a) raises questions regarding stoichiometry of such complex. Our data, taken together with large differences in abundance of NAGS, CPS1 and OTC, are consistent with clustering of the three proteins at the IMM, similar to enzymes for biosynthesis of coenzyme Q and purines Chan, et al 2015;French, et al 2016;Subramanian, et al 2019) Enzyme clustering provides metabolic advantages without the need for evolution of complimentary protein-protein interfaces (Sweetlove and Fernie 2018). Theoretical modeling and experiments with engineered proteins in E. coli show that clustering of enzymes that catalyze consecutive reactions of a metabolic pathway can increase flux through the pathway by 100-fold; this is achieved through increased local concentrations of enzymes and metabolites in the cluster (Castellana, et al 2014).…”