FREE-ENERGY SIMULATIONS OF THE HYHEL-10 HEL ANTIBODY-ANTIGEN COMPLEX/

Free energy simulations are reported for the N31(L)D mutation, both in the HyHEL-10-HEL antibody-lysozyme complex and in the unliganded anti body, using the thermodynamic-cycle perturbation method, The present s tudy suggests that the mutation would change the free energy of bindin g of the complex by -5.6 kcal/mol (unrestrained free energy simulation s), by -0.5 kcal/mol (free energy simulations with a restrained backbo ne) and by 1.8 kcal/mol (Poisson-Boltzmann calculations, which also us e a restrained geometry model). A detailed structural analysis helps i n estimating the contributions from various residues and regions of th e system, Enhanced recognition of HEL by the mutant HyHEL-10 would ari se from the combination of thermodynamically more favorable conformati onal changes of the CDR loops upon association and subsequent charge p airing with Lys96 in the antigen.