The stabilization of the CH2OCH(NH2)O- ⋯HisH+⋯-OOC triad, formed during catalysis in α-chymotrypsin and subtilisin NOVO, by the protein environment was investigated. The electrostatic lock-and-key concept was used where both the triad and the protein core were represented by their electrostatic potential calculated for a number of reference points. To obtain the electrostatic potential, we used our bond increment method developed previously. We could demonstrate that the catalytic triad is stabilized by the protein in both enzymes, i.e., a complementarity between the lock and its key exists. The fit is not perfect for α-chymotrypsin and this is due to the unfavourable effect of the backbone carbonyl group of Asn-101. We could demonstrate that the HisH+⋯-OOC diad fits better in its ion-pair form in subtilisin NOVO. The stronger stabilization for the ion-pair form than for the neutral one is also indicated by the relatively large interaction energy difference, 27.6 kJ mol-1. No such distinction could be made for α-chymotrypsin where the difference in interaction energies is only 2.8 kJ mol-1. Finally, we compared hypothetical mutants where Asp-102 (or Asp-32) are replaced by neutral Asn. The electrostatic complementarity gets considerably worse indicating that the mutants would be much less stable than the parent enzymes.
ASJC Scopus subject areas
- Condensed Matter Physics
- Physical and Theoretical Chemistry