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Pseudokinase domain of STE20-related kinase adapter protein The pseudokinase domain shows similarity to protein kinases but lacks crucial residues for catalytic activity. STRAD forms a complex with the scaffolding protein MO25, and the serine/threonine kinase (STK), LKB1, resulting in the activation of the kinase. In the complex, LKB1 phosphorylates and activates adenosine monophosphate-activated protein kinases (AMPKs), which regulate cell energy metabolism and cell polarity. LKB1 is a tumor suppressor linked to the rare inherited disease, Peutz-Jeghers syndrome, which is characterized by a predisposition to benign polyps and hyperpigmentation of the buccal mucosa. There are two forms of STRAD, alpha and beta, that complex with LKB1 and MO25. The structure of STRAD-alpha is available and shows that this protein binds ATP, has an ordered activation loop, and adopts a closed conformation typical of fully active protein kinases. It does not possess activity due to nonconservative substitutions of essential catalytic residues. ATP binding enhances the affinity of STRAD for MO25. The conformation of STRAD-alpha stabilized through ATP and MO25 may be needed to activate LKB1. The STRAD subfamily is part of a larger superfamily that includes the catalytic domains of STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",