RESUMO
Calcium/calmodulin-dependent kinase kinase 2 (CaMKK2) has been implicated in the regulation of metabolic activity in cancer and immune cells, and affects whole-body metabolism by regulating ghrelin-signalling in the hypothalamus. This has led to efforts to develop specific CaMKK2 inhibitors, and STO-609 is the standardly used CaMKK2 inhibitor to date. We have developed a novel fluorescence-based assay by exploiting the intrinsic fluorescence properties of STO-609. Here, we report an in vitro binding constant of KD â¼17 nM between STO-609 and purified CaMKK2 or CaMKK2:Calmodulin complex. Whereas high concentrations of ATP were able to displace STO-609 from the kinase, GTP was unable to achieve this confirming the specificity of this association. Recent structural studies on the kinase domain of CaMKK2 had implicated a number of amino acids involved in the binding of STO-609. Our fluorescent assay enabled us to confirm that Phe(267) is critically important for this association since mutation of this residue to a glycine abolished the binding of STO-609. An ATP replacement assay, as well as the mutation of the 'gatekeeper' amino acid Phe(267)Gly, confirmed the specificity of the assay and once more confirmed the strong binding of STO-609 to the kinase. In further characterising the purified kinase and kinase-calmodulin complex we identified a number of phosphorylation sites some of which corroborated previously reported CaMKK2 phosphorylation and some of which, particularly in the activation segment, were novel phosphorylation events. In conclusion, the intrinsic fluorescent properties of STO-609 provide a great opportunity to utilise this drug to label the ATP-binding pocket and probe the impact of mutations and other regulatory modifications and interactions on the pocket. It is however clear that the number of phosphorylation sites on CaMKK2 will pose a challenge in studying the impact of phosphorylation on the pocket unless the field can develop approaches to control the spectrum of modifications that occur during recombinant protein expression in Escherichia coli.
Assuntos
Benzimidazóis/farmacologia , Quinase da Proteína Quinase Dependente de Cálcio-Calmodulina/antagonistas & inibidores , Quinase da Proteína Quinase Dependente de Cálcio-Calmodulina/metabolismo , Corantes Fluorescentes/farmacologia , Naftalimidas/farmacologia , Inibidores de Proteínas Quinases/farmacologia , Trifosfato de Adenosina/metabolismo , Sequência de Aminoácidos , Benzimidazóis/metabolismo , Sítios de Ligação , Quinase da Proteína Quinase Dependente de Cálcio-Calmodulina/química , Calmodulina/metabolismo , Avaliação Pré-Clínica de Medicamentos/métodos , Corantes Fluorescentes/metabolismo , Humanos , Naftalimidas/metabolismo , Fosforilação , Ligação Proteica , Inibidores de Proteínas Quinases/metabolismo , Proteínas Recombinantes/química , Proteínas Recombinantes/metabolismo , Espectrometria de Fluorescência/métodosRESUMO
Calcium/calmodulin-dependent kinase kinase 2 (CaMKK2) has been implicated in a range of conditions and pathologies from prostate to hepatic cancer. Here, we describe the expression in Escherichia coli and the purification protocol for the following constructs: full-length CaMKK2 in complex with CaM, CaMKK2 'apo', CaMKK2 (165-501) in complex with CaM, and the CaMKK2 F267G mutant. The protocols described have been optimized for maximum yield and purity with minimal purification steps required and the proteins subsequently used to develop a fluorescence-based assay for drug binding to the kinase, "Using the fluorescent properties of STO-609 as a tool to assist structure-function analyses of recombinant CaMKK2" [1].