INTERNAL AND OVERALL MOTIONS OF THE TRANSLATION FACTOR EIF4E - CAP-BINDING AND INSERTION IN A CHAPS DETERGENT MICELLE

The mRNA cap-binding protein eIF4E is the limiting factor in the eIF4F translation initiation complex, which mediates the binding of the 40S ribosome to the mRNA. N-15 relaxation studies have been used to chara cterize the backbone dynamics of deuterated eIF4E in a CHAPS micelle f or the apoprotein, the m(7)GDP-bound form, and the dinucleotide (m(7)G pppA)-bound form, as well as for CHAPS-free eIF4E. Large differences i n overall correlation time between the CHAPS-free form (11.8 ns) and s amples containing different concentrations of CHAPS (15.9-19.4 ns) ind icate that eIF4E is embedded in a large micelle in the presence of CHA PS, with a total molecular weight in the range of 40-60 kDa. CHAPS see ms to restrict the mobility of the a2-b3 and a4-b5 loops which are tho ught to be embedded in the micelle. No significant changes in overall mobility were seen between the m(7)GDP-bound form, the m(7)GpppA-bound form, and the apoprotein. Amide hydrogen exchange data indicate the p resence of slowly exchanging amides in two surface-exposed helices (a2 and a4), as well as the a4-b5 loop, indicating protection by the CHAP S micelle. The micelle covers the convex side of the protein away from the cap-binding site.