Combination of Trp and Glu residues for recognition of mRNA cap structure Analysis of mG base recognition site of human cap binding protein (IF-4E) by site-directed mutagenesis

Four mutants of the human cap binding protein (hCBP), in which Trp-102, Glu-103, Asp-104 or Glu-105 was changed to the aliphatic Leu or Ala, were prepared, and their cap binding abilities were examined. Cap binding abilities of two mutants. W102L (Trp-102→Leu) and E105A (Glu-105→Ala), were significantly decreased in comparison with the wild-type hCBP. This result suggest that Trp-102 and Glu-105 are both necessary for the cap binding, and the most probable binding mode with the m⁷G of cap structure is the combination of the stacking by Trp-102 and the hydrogen-bond pairing by Glu-105, as was already proposed from the model studies.