LYK5 belongs to the protein kinase superfamily, STE Ser/Thr protein kinase family, STE20 subfamily. It contains 1 protein kinase domain. LYK5 is a pseudokinase which, in complex with CAB39, binds to and activates STK11. It relocates STK11 from the nucleus to the cytoplasm and plays an essential role in STK11-mediated G1 cell cycle arrest.