A MULTICOPY MODELING OF THE WATER DISTRIBUTION IN MACROMOLECULAR CRYSTALS

A multicopy protocol is proposed for modeling macromolecular hydration using diffraction experimental data (X-ray or neutron) to search for a better description of delocalized water sites than that given by poi nt water models. The model consists of one macromolecule and several c opies of each water molecule, refined simultaneously against diffracti on data using molecular dynamics techniques, The protocol was applied to BPTI and an RNA tetradecamer. The sites defined by the different co pies range from very ordered ones to continuous channels; they fit the density maps and agree with the diffraction amplitudes with an accura cy comparable with usual crystallographic methods. The delocalization of water in channels agrees with the high mobility observed in NMR exp eriments. (C) 1997 Wiley-Liss, Inc.