LYK5, also STE20-related Adaptor Protein (STRAD) are members of STE-20 like kinase family that are known to stimulate MAPK pathways by directly activating MAPKKK. LYK5 is a novel pseudokinase member of this family consisting of a STE-20 like kinase domain but lacks several residues that are required for its catalytic activity. It specifically binds LKB1 and plays a key role in regulating tumor suppressor activities of LKB1. It functions as an upstream activator of LKB1 and also directs the sub-cellular localization of LKB1 by anchoring it in the cytoplasm. STRAD-LKB1 interaction results in phosphorylation of STRAD and enhanced autophosphorylation of LKB1.