Peptidyl transferase activity of tRNA: A quantum chemical study

The mechanism of protein synthesis is still unknown due to inability to det ect the so-called enzyme "peptidyl transferase" even after elucidation of h igh-resolution crystal structure of ribosome. We have recently shown by mod el building and semi-empirical energy calculations that the tRNA molecule a t P-site of ribosome may act as peptidyl transferase (Das et al. (1999) J. Theor, Biol. 200, 193-205). We proposed that the tetrahedral intermediate f ormed from nucleophylic attack of CO of P-site amino-acylated tRNA by NH2 o f A-site amino-acylated tRNA is converted to a six-member ring intermediate by conformational change. This ring Intermediate produces a free tRNA aod a tRNA covalently linked to a peptide. However, energy of the six-member ri ng intermediate was calculated to be quite high. We show here that the ener gy values of all the reactants, intermediates and products are within the e xpected range when they are calculated using high level ab initio quantum c hemical methods.