Structural Basis for the Calmodulin-Mediated Activation of eEF-2K

Translation is a highly energy consumptive process 1 tightly regulated for optimal protein quality 2 and adaptation to energy and nutrient availability. A key facilitator of this process is the α-kinase eEF-2K that specifically phosphorylates the GTP-dependent translocase eEF-2, thereby reducing its affinity for the ribosome and suppressing the elongation phase of protein synthesis 3,4 . eEF-2K activation requires calmodulin binding and auto-phosphorylation at the primary stimulatory site, T348. Biochemical studies have predicted that calmodulin activates eEF-2K through a unique allosteric process 5 mechanistically distinct from other calmodulin-dependent kinases 6 . Here we resolve the atomic details of this mechanism through a 2.3 Å crystal structure of the heterodimeric complex of calmodulin with the functional core of eEF-2K (eEF-2K TR ). This structure, which represents the activated T348-phosphorylated state of eEF-2K TR , highlights how through an intimate association with the calmodulin C-lobe, the kinase creates a “spine” that extends from its N-terminal calmodulin-targeting motif through a conserved regulatory element to its active site. Modification of key spine residues has deleterious functional consequences.