How do hydrogen bonds contribute to protein-DNA recognition?

The average strength of hydrogen bonding interactions at the interface of 4 0 protein-DNA complexes comprising similar to 1500 potential hydrogen bonds and their free energies of formation have been estimated employing some re cent advances in theoretical treatments of electrostatic interactions. The hydrogen bond spatial frequency distribution shows a maximum at a proton-ac ceptor distance of 2.1 Angstrom. The corresponding average interaction ener gy and the binding free energy are computed to be -1 kcal and +4 kcal/mol.H -bond respectively. Thus hydrogen bonds do not appear to provide the drivin g force for the formation of specific complexes from initially separated pr otein and DNA but serve to optimize the interactions in the specific comple x once it is formed, via distance and angle requirements.