Enhanced interaction between pseudokinase and kinase domains in Gcn2 stimulates eIF2? phosphorylation in starved cells.
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ABSTRACT: The stress-activated protein kinase Gcn2 regulates protein synthesis by phosphorylation of translation initiation factor eIF2?, from yeast to mammals. The Gcn2 kinase domain (KD) is inherently inactive and requires allosteric stimulation by adjoining regulatory domains. Gcn2 contains a pseudokinase domain (YKD) required for high-level eIF2? phosphorylation in amino acid starved yeast cells; however, the role of the YKD in KD activation was unknown. We isolated substitutions of evolutionarily conserved YKD amino acids that impair Gcn2 activation without reducing binding of the activating ligand, uncharged tRNA, to the histidyl-tRNA synthetase-related domain of Gcn2. Several such Gcn- substitutions cluster in predicted helices E and I (?E and ?I) of the YKD. We also identified Gcd- substitutions, evoking constitutive activation of Gcn2, mapping in ?I of the YKD. Interestingly, ?I Gcd- substitutions enhance YKD-KD interactions in vitro, whereas Gcn- substitutions in ?E and ?I suppress both this effect and the constitutive activation of Gcn2 conferred by YKD Gcd- substitutions. These findings indicate that the YKD interacts directly with the KD for activation of kinase function and identify likely sites of direct YKD-KD contact. We propose that tRNA binding to the HisRS domain evokes a conformational change that increases access of the YKD to sites of allosteric activation in the adjoining KD.
SUBMITTER: Lageix S
PROVIDER: S-EPMC4014428 | biostudies-literature | 2014 May
REPOSITORIES: biostudies-literature
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