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Carbon monoxide poisoning is prevented by the energy costs of conformational changes in gas-binding haemproteins

DOI: 10.1073/pnas.1109051108 DOI Help
PMID: 21900609 PMID Help

Authors: Svetlana Antonyuk (University of Liverpool) , Neil Rustage (University of Liverpool) , C. A. Petersen (Eastern Oregon University) , J. L. Arnst (Eastern Oregon University) , Derren Heyes (University of Manchester) , R. Sharma (University of Liverpool) , Neil Berry (University of Liverpool) , Nigel Scrutton (University of Manchester) , Robert Eady (University of Liverpool) , C. R. Andrew (Eastern Oregon University) , Samar Hasnain (University of Liverpool)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Proceedings Of The National Academy Of Sciences

State: Published (Approved)
Published: September 2011

Abstract: Carbon monoxide (CO) is a product of haem metabolism and organisms must evolve strategies to prevent endogenous CO poisoning of haemoproteins. We show that energy costs associated with conformational changes play a key role in preventing irreversible CO binding. AxCYTcp is a member of a family of haem proteins that form stable 5c–NO and 6c–CO complexes but do not form O2 complexes. Structure of the AxCYTcp–CO complex at 1.25 Å resolution shows that CO binds in two conformations moderated by the extent of displacement of the distal residue Leu16 toward the haem 7-propionate. The presence of two CO conformations is confirmed by cryogenic resonance Raman data. The preferred linear Fe–C–O arrangement (170 ± 8°) is accompanied by a flip of the propionate from the distal to proximal face of the haem. In the second conformation, the Fe–C–O unit is bent (158 ± 8°) with no flip of propionate. The energetic cost of the CO-induced Leu-propionate movements is reflected in a 600 mV (57.9 kJmol-1) decrease in haem potential, a value in good agreement with density functional theory calculations. Substitution of Leu by Ala or Gly (structures determined at 1.03 and 1.04 Å resolutions) resulted in a haem site that binds CO in the linear mode only and where no significant change in redox potential is observed. Remarkably, these variants were isolated as ferrous 6c–CO complexes, attributable to the observed eight orders of magnitude increase in affinity for CO, including an approximately 10,000-fold decrease in the rate of dissociation. These new findings have wide implications for preventing CO poisoning of gas-binding haem proteins.

Journal Keywords: Bacterial; Binding; Carbon; Carbon; Crystallization; Crystallography; X-Ray; Cytochromes; Ferrous; Heme; Humans; Kinetics; Models; Chemical; Models; Molecular; Mutation; Oxidation-Reduction; Protein; Spectrum; Raman

Subject Areas: Biology and Bio-materials

Instruments: I02-Macromolecular Crystallography , I03-Macromolecular Crystallography , I04-Macromolecular Crystallography