Funding provided by NSF grant MCB-0134013 to Dr. R. Jagus and Dr. B. Joshi

Tuesday, 13 June 2006 01:43 PM -0400

eIF4E/4E-BP-Family Member Database:

Comparative analyses of eIF4E-family members

Dr. Bhavesh Joshi & Dr. Rosemary Jagus

    Translation initiation involves the recruitment of mRNA to the ribosome which is controlled by the activity of the translation factor eIF4E.  eIF4E binds to the 5’-m⁷Gppp cap-structure of mRNA.  eIF4E-activity in mRNA recruitment is dependent upon its interaction with the translation factor eIF4G which binds to the RNA-helicase eIF4A, and the ribosome associated multi-subunit factor eIF3.  The activity of eIF4E is further modulated by eIF4E-binding proteins (or 4E-BPs) which mimic the eIF4E-binding domain within eIF4G and, thus, act as competitive inhibitors of eIF4E/eIF4G interaction.  The 3D-structures of mouse, human, and yeast eIF4E bound to cap-analogues resemble ‘cupped-hands’ which sandwich cap-structures between two conserved Trp (Trp-56 and 102 for human eIF4E) residues.  A third conserved Trp is involved in recognition of the ⁷-methyl moiety of the cap-structure.

    Assessment of GenBank and dBEST databanks reveals that most organisms contain a number of proteins with homology to eIF4E.  Together with eIF4E, these structurally related proteins are part of a family of eIF4E-related proteins and, as a consequence, the vertebrate translation factor has been renamed eIF4E-1.  Through assembly of EST sequences it has been possible to identify cDNAs encoding over 400 eIF4E-family members in over 200 eukaryotic species.  Phylogenetic analyses reveal that the ancestral eIF4E gene has undergone multiple gene duplications over the course of evolution.  On the basis of amino acid substitutions relative to human eIF4E-1 Trp-56, it is possible to categorize eIF4E-family members into three different classes:  Class I eIF4E-family members contain no Trp substitutions and are found in all eukaryotes; Class II members, possess Trp→Tyr substitutions and are found in both plants and animals; whereas, Class III members possess Trp→Cys substitutions and are found in chordates.

Models of mouse eIF4E-family members eIF4E-1, eIF4E-2, and eIF4E-3 predicted using Swiss-Model.  Models are based on the crystal structure of Mouse eIF4E-1. Marcotrigiano J, Gingras AC, Sonenberg N, Burley SK (1997) Cocrystal structure of the messenger RNA 5' cap-binding protein (eIF4E) bound to 7-methyl-GDP Cell. 89, 951-61; PDB id IEJ1).Guex, N. and Peitsch, M.C. (1997) SWISS-MODEL and the Swiss-PdbViewer: An environment for comparative protein modeling. Electrophoresis 18, 2714-2723.

    The mammalian eIF4E-family Class I, Class II, and Class III eIF4E-family members share only ~30 % identity with one another.  Biochemical analyses reveal that mammalian eIF4E-2 and eIF4E-3 possess only partial activities in vitro when compared to mammalian eIF4E-1.  Both eIF4E-2 and eIF4E-3 bind to the cap-structure. eIF4E-2 interacts with 4E-BPs but not eIF4G. On the other hand, eIF4E-3 binds eIF4G but not 4E-BPs.  The structural differences allow Class II and III eIF4E-family members to discriminate between eIF4G and 4E-BPs are not known.  The aim of the eIF4E-Family Member Database is to both extend our understanding of the diversity of eIF4E-family members from organisms in all eukaryotic kingdoms, and to identify structural signatures important for eIF4E-family member activities.