Binding of a diverse set of ligands to avidin and streptavidin: an accurate quantitative prediction of their relative affinities by a combination of molecular mechanics and continuum solvent models.

We report calculations of free energies of binding, DeltaG(bind), between a diverse set of nine ligands and avidin as well as between a peptide and streptavidin using the recently developed MM/PBSA approach. This method makes use of a molecular dynamics simulation of the ligand-protein complex to generate a thermally averaged ensemble of conformations of the molecules that are involved in the complex formation. Based on this set of structures, a free energy of binding is calculated using molecular mechanical and continuum solvent energies as well as including estimates of the nonpolar solvation free energy and solute entropy. We compare in our simulations different classes of ligands, involving biotin derivatives, the dye 2-(4'-hydroxyazobenzene)benzoic acid (HABA), and a cyclic hexapeptide, which cover a large range of binding free energies from -5 to -20 kcal/mol. Our calculations are able to reproduce experimental DeltaG(bind) values with a very good correlation coefficient of r(2) = 0.92. This agreement is considerably better than the results obtained with an alternate approach, the linear interaction energy approximation, for this system (r(2) = 0.55).