biorxiv2026-11-03score 96
A ubiquinone-biosynthesis microdomain, not bulk Q supply, is required for succinate dehydrogenase in Toxoplasma that lacks Complex I
Toxoplasma gondii has no Complex I. In that mitochondrion, ubiquinone (UQ) biosynthesis proteins physically associate with parasite-specific succinate dehydrogenase (SDH) subunits and co-migrate as a high-molecular-weight assembly. Knockdown of TgCoq4 lowers SDH activity, and adding exogenous UQ to the assay does not restore it. Succinate over-reduces the UQ pool and fails to reach the uncoupler-stimulated ceiling that malate and TMPD/ascorbate can still reach. Complex III also sits with the UQ-synthesis machinery. Respiration here is organized as a biosynthesis-SDH microdomain, not as a freely mixing Q pool.
