Intramolecular interaction between sidechains in intact Trp-cage miniprotein(TC5b)

Intramolecular interaction energies of sidechains in the intact TC5b are individually computed using density fitted 2nd order Moller-Plesset perturbation theory with aug-cc-pVTZ basis set. Large intramolecular interaction energies are observed in between residue lysine(8), aspartate(9), and arginine(16). Strong attractive interaction is also observed between terminal residues. In general, the interaction energies between sidechains without the influence of solvent molecules are relatively small if the pair does not have charges. The sum of 2-body interactions between sidechains in residues1-10 and residues 11-20 are found to be attractive, consistent with the fact TC5b is known to fold at physiological pH. This is largely due to attractive interactions between the charged residues arginine(16) and aspartate(9).