Biopolymers and cell. 2001; 17 (6): 540 - 545

Specific interaction of the amino acid model carboxylic group with purine transforms it into its N7H rare tautomeric form: results of vacuum ab initio calculations

5. P. Samijlenko, T. V. Bogdan, S. A. Trygubenko, D. M. Hovorun

According to ab initio calculations (MP2/6-31G**//HF/6-31G**) In vacuum (which is an acceptable imitation of the hydrophobic medium at the sites of protein-nucleic acid contacts), specific interaction of the acetate onion (model of deprotonated residues of aspartic and glutamic acids) with the purine transforms this base from the N9H ground-state tautomeric form into the N7H high-energy tautomer (hE-EN7H-EN9H is about 4 kcul/mol) with the energy advantage of 0.46 kcal/moL The effect is achieved due to the higher complexation energy of the N7H tautomer as compared to the N9H one, which overcompensates the energy excess (about 3.90 kcal/mol) of the rare tautomer. A possible biological significance of the data obtained for more profound understanding of elementary acts of protein-nucleic acid recognition, in particular, the enzyme catalysis, is discussed.