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OH cleavage from tyrosine: debunking a myth

DOI: 10.1107/S1600577516016775 DOI Help

Authors: Charles S. Bury (University of Oxford) , Ian Carmichael (University of Notre Dame) , Elspeth F. Garman (Oxford University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Synchrotron Radiation , VOL 24 , PAGES 7 - 18

State: Published (Approved)
Published: January 2017

Abstract: During macromolecular X-ray crystallography experiments, protein crystals held at 100 K have been widely reported to exhibit reproducible bond scission events at doses on the order of several MGy. With the objective to mitigate the impact of radiation damage events on valid structure determination, it is essential to correctly understand the radiation chemistry mechanisms at play. OH-cleavage from tyrosine residues is regularly cited as amongst the most available damage pathways in protein crystals at 100 K, despite a lack of widespread reports of this phenomenon in protein crystal radiation damage studies. Furthermore, no clear mechanism for phenolic C—O bond cleavage in tyrosine has been reported, with the tyrosyl radical known to be relatively robust and long-lived in both aqueous solutions and the solid state. Here, the initial findings of Tyr –OH group damage in a myrosinase protein crystal have been reviewed. Consistent with that study, at increasing doses, clear electron density loss was detectable local to Tyr –OH groups. A systematic investigation performed on a range of protein crystal damage series deposited in the Protein Data Bank has established that Tyr –OH electron density loss is not generally a dominant damage pathway in protein crystals at 100 K. Full Tyr aromatic ring displacement is here proposed to account for instances of observable Tyr –OH electron density loss, with the original myrosinase data shown to be consistent with such a damage model. Systematic analysis of the effects of other environmental factors, including solvent accessibility and proximity to di­sulfide bonds or hydrogen bond interactions, is also presented. Residues in known active sites showed enhanced sensitivity to radiation-induced disordering, as has previously been reported.

Journal Keywords: tyrosine; specific damage; radiation chemistry; electron density loss; Fourier difference maps

Subject Areas: Biology and Bio-materials, Chemistry

Instruments: I02-Macromolecular Crystallography

Added On: 11/01/2017 11:29

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