| Eukaryotic elongation factor 2 kinase (EEF2K), also known as eEF2K or CaMKIII, is an atypical α‑kinase and the only calcium/calmodulin‑dependent member of this family, positioned as a central regulator of the elongation phase of protein synthesis by selectively phosphorylating and inhibiting its sole known substrate, eukaryotic elongation factor 2 (eEF2). The protein comprises an N‑terminal catalytic α‑kinase domain linked to a C‑terminal α‑helical regulatory region that includes sites for calmodulin binding and multiple regulatory phosphorylation sites, together forming a scaffold that integrates Ca²⁺/calmodulin, nutrient, and stress signals to modulate elongation output. Activation follows a two‑step allosteric mechanism in which Ca²⁺/calmodulin binds with high affinity to eEF2K and greatly enhances its ability to autophosphorylate Thr348 in a regulatory loop, after which phospho‑Thr348 engages a conserved basic pocket in the kinase domain and stabilizes an active loop conformation that markedly increases catalytic efficiency toward eEF2 and peptide substrates. Additional autophosphorylation at sites such as Ser500 can confer partial calcium‑independent activity while still requiring bound calmodulin, providing a means to sustain elongation control under fluctuating Ca²⁺ signals. By phosphorylating eEF2, eEF2K slows ribosomal translocation along mRNA, reducing the high energy demand of peptide chain elongation and selectively altering the synthesis of specific proteins, thereby tuning translational output in response to nutrient deprivation, hypoxia, and other forms of cellular stress. Upstream regulation places eEF2K within AMPK and mTOR signaling networks: AMPK and other stress-activated kinases promote eEF2K activity during energy depletion, while nutrient- and growth factor–driven mTORC1 signaling inhibits eEF2K via phosphorylation of negative regulatory sites, so that eEF2K activity is high during starvation and low when conditions favor growth. This integration allows eEF2K to function as an energy conservation mechanism that couples metabolic state to protein synthesis rates and, in some tissues, to autophagic responses and oxidative stress handling. In cancer, eEF2K supports the survival of rapidly proliferating cells under nutrient-poor or hypoxic conditions by limiting protein synthesis and nutrient consumption, and has been linked to progression and therapy resistance in several solid tumors, positioning it as a drug target whose inhibition may sensitize malignant cells to metabolic stress. In the nervous system, eEF2K is highly expressed in the brain and plays important roles in neuronal plasticity, cognition and synaptic function by controlling local dendritic translation; dysregulated eEF2K/eEF2 signaling has been associated with epilepsy, depression and neurodegenerative diseases including Alzheimer’s disease, where overactivation contributes to cognitive deficits and where genetic or pharmacological suppression of eEF2K improves synaptic and behavioral outcomes in preclinical models. |
