Atypical kinase involved in the biosynthesis of coenzyme Q, also named ubiquinone, an essential lipid-soluble electron transporter for aerobic cellular respiration (PubMed:25498144, PubMed:21296186, PubMed:25540914, PubMed:27499294). Its substrate specificity is unclear: does not show any protein kinase activity (PubMed:25498144, 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 (PubMed:25498144, PubMed:27499294). Shows an unusual selectivity for binding ADP over ATP (PubMed:25498144). Autoinhibited by the N-terminal domain, containing the KxGQ motif, that completely occludes the typical substrate binding pocket. Nucleotide-binding relieves inhibition (PubMed:27499294). Cofactor biosynthesis; ubiquinone biosynthesis. Homodimer; homodimerizes via its transmembrane region (PubMed:25216398). Interacts with the multi-subunit COQ enzyme complex, composed of at least COQ3, COQ4, COQ5, COQ6, COQ7 and COQ9 (PubMed:27499294, PubMed:27499296). Widely expressed, with highest levels in adrenal gland, heart, pancreas, nasal mucosa, stomach, uterus and skeletal muscle. By p53/TP53. 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 (PubMed:25498144). Nucleotide-binding opens the substrate binding pocket and flips the active site from inside the hydrophobic core into a catalytically competent, solvent-exposed posture (PubMed:27499294). The disease is caused by variants affecting the gene represented in this entry. Belongs to the protein kinase superfamily. ADCK protein kinase family.