Can soaked-in scavengers protect metalloprotein active sites from reduction during data collection?

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  2. Dr Katsuko Sato
  3. Professor Christopher Dennison
Author(s)Macedo S, Pechlaner M, Schmid W, Weik M, Sato K, Dennison C, Djinovic-Carugo K
Publication type Article
JournalJournal of Synchrotron Radiation
Year2009
Volume16
Issue2
Pages191-204
ISSN (print)0909-0495
ISSN (electronic)1600-5775
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One of the first events taking place when a crystal of a metalloprotein is exposed to X-ray radiation is photoreduction of the metal centres. The oxidation state of a metal cannot always be determined from routine X-ray diffraction experiments alone, but it may have a crucial impact on the metal's environment and on the analysis of the structural data when considering the functional mechanism of a metalloenzyme. Here, UV-Vis microspectrophotometry is used to test the efficacy of selected scavengers in reducing the undesirable photoreduction of the iron and copper centres in myoglobin and azurin, respectively, and X-ray crystallography to assess their capacity of mitigating global and specific radiation damage effects. UV-Vis absorption spectra of native crystals, as well as those soaked in 18 different radioprotectants, show dramatic metal reduction occurring in the first 60 s of irradiation with an X-ray beam from a third-generation synchrotron source. Among the tested radioprotectants only potassium hexacyanoferrate(III) seems to be capable of partially mitigating the rate of metal photoreduction at the concentrations used, but not to a sufficient extent that would allow a complete data set to be recorded from a fully oxidized crystal. On the other hand, analysis of the X-ray crystallographic data confirms ascorbate as an efficient protecting agent against radiation damage, other than metal centre reduction, and suggests further testing of HEPES and 2,3-dichloro-1,4-naphtoquinone as potential scavengers.
PublisherWiley-Blackwell Munksgaard
URLhttp://dx.doi.org/10.1107/S0909049509003331
DOI10.1107/S0909049509003331
NotesResearch Support, Non-U.S. Gov't Denmark
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