Local control of a disorder-order transition in 4E-BP1 underpins regulation of translation via Eif4e

摘要

The molecular mechanism underpinning regulation of eukaryotic translation initiation factor elF4E by 4E-BP1 has remained unclear. We use isothermal calorimetry, circular dichroism, NMR, and computational rnmodeling to analyze how the structure of the elF4E-binding domain rnof 4E-BP1 determines its affinity for the dorsal face of elF4E and thus the ability of this regulator to act as a competitive rninhibitor. This work identifies the key role of solvent-facing amino acids in 4E-BP1 that are not directly engaged in interactions with elF4E, These amino acid residues influence the propensity of the natively unfolded binding motif to fold into a conformation, including a stretch of a-helix, that is required for tight binding to elF4E. In so doing, they contribute to a free energy landscape for 4E-BP1 folding that is poised so that phosphorylation of S65 at the C-terminal end of the helical region can modulate the propensity rnof folding, and thus regulate the overall free energy of 4E-BP1 binding to elF4E, over a physiologically significant range. Thus, phosphorylation acts as an intramolecular structural modulator that biases the free energy landscape for the disorder-order transition rnof 4E-BP1 by destabilizing the a-helix to favor the unfolded form that cannot bind elF4E. This type of order-disorder regulatory mechanism is likely to be relevant to other intermolecular regulatory rnphenomena in the cell.