Serial crystallography captures enzyme catalysis in copper nitrite reductase at atomic resolution from one crystal

• Published in: IUCrJ 2016-07, Vol.3 (Pt 4), p.271-281
• Main Authors: Horrell, Sam, Antonyuk, Svetlana V, Eady, Robert R, Hasnain, S Samar, Hough, Michael A, Strange, Richard W
• Format: Article
• Language: English
• Subjects: Catalysis; Chemical properties; Copper compounds; copper nitrite reductase; Crystallography; denitrification; enzyme mechanism; Methods; MSOX; Nitrites; Observations; radiation damage; radiolysis; Research Papers; serial crystallography; synchrotron radiation; XFEL
• ISSN: 2052-2525; 2052-2525
• DOI: 10.1107/s205225251600823x

Relating individual protein crystal structures to an enzyme mechanism remains a major and challenging goal for structural biology. Serial crystallography using multiple crystals has recently been reported in both synchrotron-radiation and X-ray free-electron laser experiments. In this work, serial crystallography was used to obtain multiple structures serially from one crystal (MSOX) to study in crystallo enzyme catalysis. Rapid, shutterless X-ray detector technology on a synchrotron MX beamline was exploited to perform low-dose serial crystallography on a single copper nitrite reductase crystal, which survived long enough for 45 consecutive 100 K X-ray structures to be collected at 1.07-1.62 Å resolution, all sampled from the same crystal volume. This serial crystallography approach revealed the gradual conversion of the substrate bound at the catalytic type 2 Cu centre from nitrite to nitric oxide, following reduction of the type 1 Cu electron-transfer centre by X-ray-generated solvated electrons. Significant, well defined structural rearrangements in the active site are evident in the series as the enzyme moves through its catalytic cycle, namely nitrite reduction, which is a vital step in the global denitrification process. It is proposed that such a serial crystallography approach is widely applicable for studying any redox or electron-driven enzyme reactions from a single protein crystal. It can provide a 'catalytic reaction movie' highlighting the structural changes that occur during enzyme catalysis. The anticipated developments in the automation of data analysis and modelling are likely to allow seamless and near-real-time analysis of such data on-site at some of the powerful synchrotron crystallographic beamlines.