Distinct features of cap binding by eIF4E1b proteins.
Bottom Line: Moreover, eIF4E1b proteins are distinguishable from eIF4E1a by a set of conserved amino acid substitutions, several of which are located near to cap-binding residues.Indeed, eIF4E1b possesses several distinct features, namely, enhancement of cap binding by a benzyl group at N(7) position of guanine, a reduced response to increasing length of the phosphate chain and increased binding to a cap separated by a linker from Sepharose, suggesting differences in the arrangement of the protein's core.In agreement, mutagenesis of the amino acids differentiating eIF4E1b from eIF4E1a reduces cap binding by eIF4E1a 2-fold, demonstrating their role in modulating cap binding.
Affiliation: Division of Biophysics, Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Warsaw 02-089, Poland. Electronic address: firstname.lastname@example.org.Show MeSH
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Mentions: Our analysis of vertebrate eIF4E1a and eIF4E1b sequences identified the amino acids that consistently differentiate the two groups of proteins (Fig. 1). Moreover, the three-dimensional model structure of XeIF4E1b with m7GTP showed that some of these residues are proximal to the amino acids that bind the cap (Fig. 5a). These include Ser86(Met), Ser87(Pro), Ser105(Glu), Arg106(Lys), Ala199(Ser), Leu210(Thr) and Ser211(Thr) (XeIF4E1b numbering, in brackets are shown the eIF4E1a amino acids). We hypothesized that these residue changes in eIF4E1b are a significant factor in its lower cap-binding affinity. The presence in eIF4E1b of Ser105 and Arg106 instead of Glu and Lys may directly influence the position of Trp102 and hence modify the stacking interaction with the cap. Additionally, Ala199 in place of Ser may induce changes in the orientation of the Trp102 indole ring by influencing the position of His200 located close to Trp102. Furthermore, cap-binding stacking interaction may be weakened by changes of the Trp56 environment, resulting from alterations in the position of Phe48 likely induced by the presence Ser86 and Ser87 instead of Met and Pro, respectively. Replacement of Thr in positions 210 and 211 by Leu and Ser is also likely to be important, as they are located in the C-terminal loop responsible for binding the phosphate chain and second cap nucleoside.
Affiliation: Division of Biophysics, Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Warsaw 02-089, Poland. Electronic address: email@example.com.