期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 108, 期 38, 页码 15780-15785出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1109051108
关键词
sensors; crystallography; kinetics; ligand discrimination; atomic resolution
资金
- Biotechnology and Biological Sciences Research Council (BBSRC) [B15474, REI20571]
- Cross-Faculties of the University
- National Science Foundation [MCB-0745035]
- Royal Society
- Direct For Biological Sciences
- Div Of Molecular and Cellular Bioscience [0745035] Funding Source: National Science Foundation
- Biotechnology and Biological Sciences Research Council [B15474, BB/D01963X/1] Funding Source: researchfish
- BBSRC [BB/D01963X/1] Funding Source: UKRI
Carbon monoxide (CO) is a product of haem metabolismand 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 angstrom 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 degrees) 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 degrees) with no flip of propionate. The energetic cost of the CO-induced Leupropionate 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 angstrom 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.
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