Atypical kinase involved in the biosynthesis of coenzyme Q, also named ubiquinone, an essential lipid-soluble electron transporter for aerobic cellular respiration. Its substrate specificity is unclear: does not show any protein kinase activity. Probably acts as a small molecule kinase, possibly a lipid kinase that phosphorylates a prenyl lipid in the ubiquinone biosynthesis pathway, as suggested by its ability to bind coenzyme Q lipid intermediates. Shows an unusual selectivity for binding ADP over ATP. Autoinhibited by the N-terminal domain, containing the KxGQ motif, that completely occludes the typical substrate binding pocket. Nucleotide-binding relieves inhibition. Cofactor biosynthesis; ubiquinone biosynthesis. Homodimer; homodimerizes via its transmembrane region. Interacts with the multi-subunit COQ enzyme complex. Adopts an atypical protein kinase-like fold: while it adopts a core fold similar to that of well-characterized protein kinase-like domains. The KxGQ motif completely occludes the typical substrate binding pocket. Nucleotide-binding opens the substrate binding pocket and flips the active site from inside the hydrophobic core into a catalytically competent, solvent-exposed posture. Belongs to the protein kinase superfamily. ADCK protein kinase family.