Structural Effects of Radiation Damage and Its Potential for Phasing

A detailed analysis of radiation-damage-induced structural and intensity changes is presented on the model protein thaumatin. Changes in reflection intensities induced by irradiation display a parabolic character. The most pronounced structural changes observed were disulfide-bond breakage and associated main-chain and side-chain movements as well as decarboxylation of aspartate and glutamate residues. The structural changes induced on the sulfur atoms were successfully used to obtain high-quality phase estimates via an RIP procedure. Results obtained with ACORN suggest that the contribution originating from the partial structure may play an important role in phasing even at less than atomic resolution.