INTERACTION OF INDOLE-DERIVATIVES WITH BIOLOGICALLY IMPORTANT AROMATIC-COMPOUNDS .22. IMPORTANCE OF SIMULTANEOUS COOPERATION OF HYDROGEN-BOND PAIRING AND STACKING INTERACTIONS FOR RECOGNITION OF GUANINE BASE BY A PEPTIDE - X-RAY CRYSTAL ANALYSIS OF 7-METHYLGUANOSINE-5'-PHOSPHATE TRYPTOPHANYLGLUTAMIC ACID COMPLEX

As a model to investigate the mode of recognition of the base guanine by peptides and proteins, the crystal structure of the 7-methylguanosine-5'-phosphate-tryptophanylglutamic acid complex was analysed by X-ray diffraction; this is the first crystal structure determination of a peptide-nucleotide complex. The complex crystals are stabilized by extensive hydrogen-bond formation in which three independent water molecules per complex pair participate. Both molecules are joined by the coupled contributions of the triple hydrogen bonds between the guanine base and the peptide backbone chain and of the prominent stacking interactions between the guanine base and the tryptophan indole side-chain, suggesting the importance of the coupling of hydrogen bonding and stacking interactions for recognition of the base to occur.