Local control of a disorder—order transition in 4E-BP1 underpins regulation of translation via eIF4E

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 107; no. 41; pp. 17627 - 17632
• Main Authors: Tait, Shirley, Dutta, Kaushik, Cowburn, David, Warwicker, Jim, Doig, Andrew J., McCarthy, John E. G.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 12-10-2010; National Acad Sciences
• Subjects: Adaptor Proteins, Signal Transducing - metabolism; Amino acids; Binding sites; Binding Sites - genetics; Biological Sciences; Calorimetry; Chemical equilibrium; Circular Dichroism; Computational Biology - methods; Electrostatics; Eukaryotes; Eukaryotic Initiation Factor-4E - metabolism; Eukaryotic initiation factors; Free energy; Gene Expression Regulation - physiology; Humans; Mass Spectrometry; Messenger RNA; Models, Molecular; Nuclear Magnetic Resonance, Biomolecular; Phosphoproteins - metabolism; Phosphors; Phosphorylation; Physiological regulation; Protein Binding; Protein Conformation; Protein folding; Proteins; Static Electricity
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1008242107

The molecular mechanism underpinning regulation of eukaryotic translation initiation factor eIF4E by 4E-BP1 has remained unclear. We use isothermal calorimetry, circular dichroism, NMR, and computational modeling to analyze how the structure of the eIF4E-binding domain of 4E-BP1 determines its affinity for the dorsal face of eIF4E and thus the ability of this regulator to act as a competitive inhibitor. This work identifies the key role of solvent-facing amino acids in 4E-BP1 that are not directly engaged in interactions with eIF4E. These amino acid residues influence the propensity of the natively unfolded binding motif to fold into a conformation, including a stretch of α-helix, that is required for tight binding to eIF4E. 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 of folding, and thus regulate the overall free energy of 4E-BP1 binding to eIF4E, over a physiologically significant range. Thus, phosphorylation acts as an intramolecular structural modulator that biases the free energy landscape for the disorder—order transition of 4E-BP1 by destabilizing the α-helix to favor the unfolded form that cannot bind eIF4E. This type of order—disorder regulatory mechanism is likely to be relevant to other intermolecular regulatory phenomena in the cell.