biostudies-literatureAntonyuk SVBiotechnology and Biological Sciences Research Council15780-5https://www.ebi.ac.uk/biostudies/studies/S-EPMC3179090biostudies-literatureUnknown108(38)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 O(2) 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 thProceedings of the National Academy of Sciences of the United States of AmericaCarbon monoxide poisoning is prevented by the energy costs of conformational changes in gas-binding haemproteins.PMC3179090B15474BB/D01963X/1REI20571Scrutton NSPetersen CARustage NEady RRAntonyuk SVHeyes DJHasnain SSArnst JLSharma RBerry NGAndrew CRfalseCarbon monoxide poisoning is prevented by the energy costs of conformational changes in gas-binding haemproteins.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 O(2) 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 th2011-01-01T00:00:00Z2011 Sep2026-04-07T14:13:49.716Z2019-03-27T00:44:13ZS-EPMC31790902190060910.1073/pnas.1109051108