Anti-hydroxylysine kinase antibodies are used in the immunodetection of the protein encoded by the HYKK gene. In humans, the canonical protein has a reported length of 373 amino acid residues and a mass of 41.9 kDa. Its subcellular localization is in the cytoplasm. Alternative splicing is reported to yield 3 different isoforms for this protein. A member of the Aminoglycoside phosphotransferase protein family, it is known to catalyze the GTP-dependent phosphorylation of 5-hydroxy-L-lysine. Other names for this target antigen include 5-hydroxylysine kinase, aminoglycoside phosphotransferase domain-containing protein 1, and 5-hydroxy-L-lysine kinase.