A SELECTIVE RECOGNITION MODE OF A NUCLEIC-ACID BASE BY AN AROMATIC AMINO-ACID - L-PHENYLALANINE-7-METHYLGUANOSINE 5'-MONOPHOSPHATE STACKING INTERACTION

The conformation of 7-methylguanosine 5''-monophosphate (m7GMP) and its interaction with L-phenylalanine (Phe) have been investigated by X-ray crystallographic, 1H-nuclear magnetic resonance, and energy calculation methods. The N(7) methylation of the guanine base shifts m7GMP toward an anti-gauche,gauche conformation about the glycosyl and exocyclic C(4'').sbd.C(5'') bonds, respectively. The prominent stacking observed between the benzene ring of Phe and guanine base of m7GMP is primarily due to the N(7) quarternization of the guanine base. The formation of a hydrogen bonding pair between the anionic carboxyl group and the guanine base further stabilizes this stacking interaction. The present results imply the importance of aromatic amino acids as a hallmark for the selective recognition of a nucleic acid base.