Drug discovery and design based on molecular mimicry

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The recent progress in molecular and structural biology of translational apparatus has uncovered a novel biological phenomenon of macromolecular, mimicry between protein and tRNA. The 3D structures of translational elongation factor EF- G and ribosome recycling factor RRF are shown to mimic a tRNA shape. Another, even more sophisticated, example may be polypeptide release factors that are shown to possess a tripeptide anticodon' to decipher stop codons in mRNA, showing an impressive mimic of tRNA function. Clearly, this concept should provide us with a novel clue to design or selection of therapeutic RNA molecules that mimic protein targets.The systematic evolution of ligands by exponential enrichment (SELEX) method is based on the in vitro selection oligo-nucleotide; ligands from large random-sequence libraries by repeated reactions of DNA transcription, RNA selection and RT-PCR amplification. The selected oligo-nucleotide ligands are called 'aptamer', which has. High affinity and specificity to the target molecule. We have initiated SELEX experiments using mammalian translation initiation factors including eIF4G and eIF4A. Several RNA aptamers that acquired the strong and specific binding capacity for these proteins were successfully raised. One class of eIF4A aptamers exhibits a high affinity with.el4A1 and severely inhibits the ATPasc activity, suggesting that they probably dock the catalytic pocket. Furthermore, these aptamers inhibit can dependent protein synthesis in a cell free translation system. This inhibition was reversed by addition of purified eIF4A1 suggesting that RNA aptamers to eIF4A1 inhibits its activity in the cell lysate.Importantly the abnormality in the protein level or the activity of either initiation factor is known cause cell proliferation. Hence, from the therapeutic point of view, it is of great interest whether or not these RNA aptamers can suppress these malignant cells.