CaMKK2 kinase domain interacts with the autoinhibitory region through the N-terminal lobe including the RP insert
Abstract
Background: Calcium/calmodulin-dependent protein kinase kinase 2 (CaMKK2), a member of the Ca2+/calmodulin-dependent kinase (CaMK) family, functions as an upstream activator of CaMKI, CaMKIV and AMP activated protein kinase. Thus, CaMKK2 is involved in the regulation of several key physiological and pathophysiological processes.
Previous studies have suggested that Ca2+/CaM binding may cause unique conformational changes in the CaMKKs compared with other CaMKs. However, the underlying mechanistic details remain unclear.
Methods: In this study, hydrogen-deuterium exchange coupled to mass spectrometry, time-resolved fluorescence spectroscopy, small-angle x-ray scattering and chemical cross-linking were used to characterize Ca2+/CaM binding-induced structural changes in CaMKK2. Results: Our data suggest that: (i) the CaMKK2 kinase domain interacts with the autoinhibitory region (AID) through the N-terminal lobe of the kinase domain including the RP insert, a segment important for targeting downstream substrate kinases; (ii) Ca2+/CaM binding affects the structure of several regions surrounding the ATP-binding pocket, including the activation segment; (iii) although the CaMKK2:Ca2+/CaM complex shows high conformational flexibility, most of its molecules are rather compact; and (iv) AID-bound Ca2+/CaM transiently interacts with the CaMKK2 kinase domain.
Conclusions: Interactions between the CaMKK2 kinase domain and the AID differ from those of other CaMKs. In the absence of Ca2+/CaM binding the autoinhibitory region inhibits CaMKK2 by both blocking access to the RP insert and by affecting the structure of the ATP-binding pocket.
General significance: Our results corroborate the hypothesis that Ca2+/CaM binding causes unique conformational changes in the CaMKKs relative to other CaMKs.