Atypical kinase involved in the biosynthesis of coenzyme Q, also named ubiquinone, an essential lipid-soluble electron transporter for aerobic cellular respiration (PubMed:27499294). Its substrate specificity is unclear: does not show any protein kinase activity (PubMed:27499294). 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 (By similarity). Shows an unusual selectivity for binding ADP over ATP (By similarity). 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, composed of at least COQ3, COQ4, COQ5, COQ6, COQ7 and COQ9. Present in various tissues (at protein level). Adopts an atypical protein kinase-like fold: while it adopts a core fold similar to that of well-characterized protein kinase-like domains, a number of features are positioned to inhibit the kinase activity: (1) an atypical AAAS motif in an alanine-rich (A-rich) loop that replaces the canonical glycine-rich (G-rich) nucleotide-binding loop and limits ATP binding by establishing an unusual selectivity for ADP and (2) an N-terminal domain, containing the KxGQ motif, that 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. Mice were born at the expected Mendelian frequency and do not show overt phenotype under normal conditions. They however develop a slowly progressive loss of coordination after birth and develop ataxia and seizures. Defects are due to dysfunctional cerebellar Purkinje cells and defective skeletal muscle. Mice display tissue-specific coenzyme Q deficiency: coenzyme Q levels are normal in younger mice but significantly and specifically reduced in skeletal muscle. However, normal coenzyme Q levels are observed in whole cerebella, suggesting that cerebellar Purkinje cells are specifically affected. Belongs to the protein kinase superfamily. ADCK protein kinase family.