Tryptophan Residues from Cap Binding Slot in eIF4E Family Members: Their Contributions to Near-UV Circular Dichroism Spectra

Abstract

eIF4E, a key factor in the cap-dependent translation initiation, binds cap structure at the 5’ end of mRNA by stacking interaction involving two of its eight conserved tryptophan residues. In this paper, we examined individual contributions of tryptophan residues to the near-UV Circular Dichroism spectra to identify structural similarities and differences in cap binding motif among members of eIF4E family. The near-UV CD spectrum of human eIF4E1a in its apo form, resulting mainly from 1Lb transition and dominated by two vibrionic bands, is conserved among eIF4Es. Based on comparison of CD spectra for eIF4E mutants, we showed that tryptophans involved in stacking interaction give strongest individual contributions, which allow identification of their different orientation with respect to the cap. This indicates that near-UV CD is a quick and powerful tool to analyse tryptophan conformation in eIF4E proteins, and their changes upon binding modified cap analogues.