title: Radiation decay of thaumatin crystals at three X-ray energies.
abstract: Radiation damage is an unavoidable obstacle in X-ray crystallographic data collection for macromolecular structure determination, so it is important to know how much radiation a sample can endure before being degraded beyond an acceptable limit. In the literature, the threshold at which the average intensity of all recorded reflections decreases to a certain fraction of the initial value is called the `dose limit'. The first estimated D50 dose-limit value, at which the average diffracted intensity was reduced to 50%, was 20 MGy and was derived from observing sample decay in electron-diffraction experiments. A later X-ray study carried out at 100 K on ferritin protein crystals arrived at a D50 of 43 MGy, and recommended an intensity reduction of protein reflections to 70%, D70, corresponding to an absorbed dose of 30 MGy, as a more appropriate limit for macromolecular crystallography. In the macromolecular crystallography community, the rate of intensity decay with dose was then assumed to be similar for all protein crystals. A series of diffraction images of cryocooled (100 K) thaumatin crystals at identical small, 2° rotation intervals were recorded at X-ray energies of 6.33 , 12.66 and 19.00 keV. Five crystals were used for each wavelength. The decay in the average diffraction intensity to 70% of the initial value, for data extending to 2.45 Å resolution, was determined to be about 7.5 MGy at 6.33 keV and about 11 MGy at the two higher energies.
authors: Structural Biology Research Center, Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba, Japan.
authors: Dorothee
authors: D
authors: Liebschner
authors: Department of Biochemistry, University of Georgia and Structural Biology Center, Argonne National Laboratory, Argonne, IL 60439, USA.
authors: Gerold
authors: G
authors: Rosenbaum
authors: Leidos Biomedical Research Inc., Basic Science Program, Argonne National Laboratory, Argonne, IL 60439, USA.
authors: Miroslawa
authors: M
authors: Dauter
authors: Synchrotron Radiation Research Section, MCL, National Cancer Institute, Argonne National Laboratory, Argonne, IL 60439, USA.
authors: Zbigniew
authors: Z
authors: Dauter
mesh_terms: D003460:Crystallization; D018360:Crystallography, X-Ray / Q000379:methods*; D010940:Plant Proteins / Q000737:chemistry*; D010944:Plants / Q000737:chemistry*
chemical_list: D010940:Plant Proteins; C003427:thaumatin protein, plant
keywords: dose limit; energy dependence; radiation damage