Solution-based approach to study binding to the eIF4E cap-binding site using CD spectroscopy

The eukaryotic initiation factor 4E (eIF4E) is the key component of the translational initiation complex that recruits mRNA by binding to a unique “cap” structure located at the 5′ end of the mRNA. Overexpression of eIF4E has been implicated in the development of cancer, potentially as a result of increasing the cellular levels of proteins involved in processes that include proliferation and regulation of apoptosis. As a result, the cap-binding site of eIF4E has become a target for the development of anti-cancer therapeutics. The structure of eIF4E bound to the cap mimic 7-methyl-GDP revealed that two tryptophans from different loops in eIF4E sandwiched the 7-methylguanine group between them. This interaction gives rise to a strong exciton coupling signal between the two tryptophans that can be visualized by CD spectroscopy. eIF4E is a challenging protein to work with because of a propensity to aggregate under conditions used in biophysical techniques. CD spectroscopy provides a gentle, solution-based approach to study binding to the cap-binding site of eIF4E. Evidence is provided that the exciton coupling signal can be used to both qualitatively and quantitatively analyze the binding of cap analogs to eIF4E.