A Mutant of Eukaryotic Protein Synthesis Initiation Factor eIF4EK119A Has an Increased Binding Affinity for both m7G Cap Analogues and eIF4G Peptides

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Abstract
The eukaryotic multisubunit initiation factor eIF4F is an essential component of the translational machinery. Recognition of the cap structure of mRNA, m7GpppN, where N is any nucleotide, by eIF4E is required for initiation of translation. Here we compare the equilibrium and thermodynamic binding characteristics of wild-type eIF4E and a high-affinity mutant, eIF4EK119A, with those of cap analogues and eIF4G peptides. The temperature-dependent Kd values for cap analogues were markedly lower, indicating tighter binding, with the eIF4EK119A mutant compared with wild-type eIF4E. Although interactions with cap analogues were found to be enthalpically driven, entropic contributions were also significant. Moreover, the binding affinities of eIF4G peptides were 2−4-fold tighter for eIF4EK119A than for eIF4Ewt. These results demonstrate that the binding affinity for both the mRNA cap and eIF4G peptides can be simultaneously altered by point mutations distant from either binding site. Entropic contributions to binding suggesting hydrophobic interactions are larger in the mutant protein and are most likely due to a conformational change.