Heme enzymes. Neutron cryo-crystallography captures the protonation state of ferryl heme in a peroxidase.

Journal article

Heme enzymes activate oxygen through formation of transient iron-oxo (ferryl) intermediates of the heme iron. A long-standing question has been the nature of the iron-oxygen bond and, in particular, the protonation state. We present neutron structures of the ferric derivative of cytochrome c peroxidase and its ferryl intermediate; these allow direct visualization of protonation states. We demonstrate that the ferryl heme is an Fe(IV)=O species and is not protonated. Comparison of the structures shows that the distal histidine becomes protonated on formation of the ferryl intermediate, which has implications for the understanding of O-O bond cleavage in heme enzymes. The structures highlight the advantages of neutron cryo-crystallography in probing reaction mechanisms and visualizing protonation states in enzyme intermediates.

Authors: Casadei, C; Gumiero, A; Metcalfe, C; Murphy, E; Basran, J

• Publication status: Published
• Journal: Science (New York, N.Y.)
• Volume: 345
• Issue: 6193
• Pages: 193-197
• Publication date: 2014-07-01
• DOI: 10.1126/science.1254398
• EISSN: 1095-9203
• ISSN: 0036-8075
• Language: English
• Keywords: Protons; Neutrons; Cytochrome-c Peroxidase; Iron; Heme; Crystallography, X-Ray; Histidine; Oxygen; Neutron Diffraction