Complicated water orientations in the minor groove of the B-DNA decamer d(CCATTAATGG)2 observed by neutron diffraction measurements

It has long been suspected that the structure and function of a DNA duplex can be strongly dependent on its degree of hydration. By neutron diffraction experiments, we have succeeded in determining most of the hydrogen ( H) and deuterium ( D) atomic positions in the decameric d( CCATTAATGG)(2) duplex. Moreover, the D positions in 27 D2O molecules have been determined. In particular, the complex water network in the minor groove has been observed in detail. By a combined structural analysis using 2.0 angstrom resolution X-ray and 3.0 angstrom resolution neutron data, it is clear that the spine of hydration is built up, not only by a simple hexagonal hydration pattern ( as reported in earlier X-ray studies), but also by many other water bridges hydrogen- bonded to the DNA strands. The complexity of the hydration pattern in the minor groove is derived from an extraordinary variety of orientations displayed by the water molecules.