title: What can be done with a good crystal and an accurate beamline?
abstract: X-ray single-wavelength anomalous diffraction (SAD) data from a crystal of proteinase K were collected using synchrotron radiation of 0.98 A wavelength at SER-CAT 22-ID beamline, Advanced Photon Source, Argonne National Laboratory. At this wavelength, the expected Bijvoet ratio resulting from the presence of one calcium, one chloride and ten S atoms in the 279-residue protein is extremely small at approximately 0.46%. The direct-methods program SHELXD located 11 anomalous sites using data truncated to 2 A resolution. SHELXE was used to produce an easily interpretable electron-density map. This study shows that an accurate beamline and a good-quality crystal provide the possibility of successfully using a very weak anomalous signal of sulfur measured at a short wavelength for phasing a protein structure, even if a small degree of radiation damage is present.
authors.affiliation: SAIC-Frederick Inc., Basic Research Program, Argonne National Laboratory, Argonne, IL 60439, USA.
authors.forename: Jiawei
authors.initials: J
authors.lastname: Wang
authors.forename: Miroslawa
authors.initials: M
authors.lastname: Dauter
authors.forename: Zbigniew
authors.initials: Z
authors.lastname: Dauter
mesh_terms: D020134:Catalytic Domain; D003460:Crystallization; D018360:Crystallography, X-Ray; D004583:Electrons; D019286:Endopeptidase K / Q000737:chemistry*; D008958:Models, Molecular; D011827:Radiation
chemical_list: D019286:Endopeptidase K