title: Radiation-induced site-specific damage of mercury derivatives: phasing and implications.
abstract: The behavior of mercury-derivatized triclinic crystals of a 60 kDa protein target from the New York Structural GenomiX Research Consortium provides novel insights into the mechanism of heavy-atom-specific radiation damage and its potential exploitation for de novo structure solution. Despite significant anomalous signal, structure solution by classic SAD and MAD phasing approaches was not successful. A detailed analysis revealed that significant isomorphic variation of the diffracted intensities was induced by X-ray irradiation. These intensity changes allowed the crystal structure to be solved by the radiation-damage-induced phasing (RIP) technique. Inspection of the crystal structure and electron-density maps demonstrated that the covalent S-Hg bonds at all four derivatized cysteine sites were much more susceptible to radiation-induced cleavage than other bonds typically present in native proteins. A simple diagnostic is described to identify the fingerprint of such decay at the time of data collection/processing. The rapid radiation-induced decomposition of mercury adducts is consistent with the difficulties frequently associated with the experimental phasing of mercury derivatives and suggests a straightforward solution to overcome this limitation by radiation-damage-induced phasing with anomalous scattering (RIPAS). These results indicate that historically recalcitrant and newly emerging difficulties associated with Hg phasing should be revisited.
authors.affiliation: Department of Biochemistry, Albert Einstein College of Medicine, Yeshiva University, Bronx, NY 10461, USA. acharya@bnl.gov
authors.forename: Udupi A
authors.initials: UA
authors.lastname: Ramagopal
authors.forename: Zbigniew
authors.initials: Z
authors.lastname: Dauter
authors.forename: Radhakannan
authors.initials: R
authors.lastname: Thirumuruhan
authors.forename: Elena
authors.initials: E
authors.lastname: Fedorov
authors.forename: Steven C
authors.initials: SC
authors.lastname: Almo
mesh_terms: D003460:Crystallization; D018360:Crystallography, X-Ray / Q000379:methods; D008628:Mercury / Q000528:radiation effects*; D011506:Proteins / Q000737:chemistry / Q000528:radiation effects*; D011827:Radiation
chemical_list: D011506:Proteins; D008628:Mercury