Differential AMP-activated protein kinase (AMPK) recognition mechanism of Ca²⁺/calmodulin-dependent protein kinase kinase isoforms

Ca²⁺/calmodulin-dependent protein kinase kinase β (CaMKKβ) is a known activating kinase for AMP-activated protein kinase (AMPK). In vitro, CaMKKβ phosphorylates Thr¹⁷² in the AMPKα subunit more efficiently than CaMKKα, with a lower K_m (∼2 μM) for AMPK, whereas the CaMKIα phosphorylation efficiencies by both CaMKKs are indistinguishable. Here we found that subdomain VIII of CaMKK is involved in the discrimination of AMPK as a native substrate by measuring the activities of various CaMKKα/CaMKKβ chimera mutants. Site-directed mutagenesis analysis revealed that Leu³⁵⁸ in CaMKKβ/Ile³²² in CaMKKα confer, at least in part, a distinct recognition of AMPK but not of CaMKIα.