The AMP-activated protein kinase (AMPK) is a critical regulator of cellular and whole-body energy metabolism that synchronizes metabolic processes to balance nutrient supply with energy demand. An important upstream regulator of AMPK is the Ca2+-calmodulin dependent protein kinase kinase-2 (CaMKK2), which activates AMPK in response to elevations in intracellular Ca2+. In the hypothalamus, the CaMKK2-AMPK signaling pathway is critical for mediating the effects of hormones and neuroendocrine signals, which co-ordinate crosstalk between metabolic tissues to regulate appetite and whole-body energy metabolism. Despite its importance, little is known about the molecular mechanisms controlling CaMKK2 beyond its regulation by Ca2+-CaM.
Inhibition of the Ca2+-calmodulin dependent protein kinase kinase-2 (CaMKK2) protects against high-fat diet induced glucose intolerance, insulin resistance and weight gain, however the link between lipid metabolism and CaMKK2 is poorly understood. We have discovered that CaMKK2 is directly activated by the major metabolic intermediate palmitoyl-CoA in a Ca2+-CaM independent manner. Activation by palmitoyl-CoA is dependent upon a molecular signature we have identified called a G4-P2P motif, which comprises a glycine tetrad (G4) and tandem proline residues (P2P) located within the C-terminal sequence of CaMKK2. Bioinformatic analysis revealed the G4-P2P motif occurs in over 200 proteins encoded by the human genome including the metabolic regulator acetyl-CoA carboxylase, which is allosterically inhibited by palmitoyl-CoA. Intriguingly, the G4-P2P motif also occurs within the carbohydrate-binding module (CBM) of the AMPK beta1 subunit close to the Allosteric Drug and Metabolite (ADaM) binding site. We further show that AMPK-beta1 complexes are directly activated by palmitoyl-CoA, whereas beta2-complexes are insensitive. Our findings indicate that both CaMKK2 and AMPK in addition to directly sensing Ca2+ and intracellular energy, respectively, are also sensors of cellular lipid fuel.