Binding Site Specifics and Effects of Use
4EGI-1, like 4E-BP polypeptides, displaces eIF4G by associating with a binding site on E. Not only does the synthetic molecule prevent the association between the two initiation factors, but by binding to a different portion of E via the same motif, it has been shown to actually increase the binding affinity of E for endogenous (originating within an organism) 4E-BP1.1 The Harvard research group leading the study screened 16,000 compounds, looking for one that would displace a fluorescein-labeled peptide derived from the G sequence that binds to the E form at the same site. Eventually they turned up 4EGI-1, which displaced eIF4G by binding to a smaller subset of its binding site (on E). The newly found molecule had the added advantage of enhancing 4E-BP1 binding, a surprise given that this molecule is also believed to bind eIF4E via the same motif. It appears that by displacing the G sequence without blocking the entire binding interface of E, 4EGI-1 is able to clear the “docking site” of the endogenous regulator.
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