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

• DOI: 10.1126/science.1254398
• Publication Date: 2014-07-10T20:59:53Z
• Authors: Cecilia M. Casadei; Andrea Gumiero; Clive L. Metcalfe; Emma J. Murphy; Jaswir Basran; Maria Grazia Conc...; Susana C. M. Teix...; Tobias E. Schrader; Alistair J. Fielding; Andreas Ostermann; Matthew P. Blakeley; Emma L. Raven; Peter C. E. Moody
• Keywords: Neutrons; 0301 basic medicine; Crystallography; Iron; 500; Heme; Cytochrome-c Peroxidase; 540; Oxygen; Neutron Diffraction; QH301; 03 medical and health sciences; X-Ray; Histidine; QD; Protons

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