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Is cooperative oxygen binding by hemoglobin really understood?

Abstract

The enormous success of structural biology challenges the physical scientist. Can biophysical studies provide a truly deeper understanding of how a protein works than can be obtained from static structures and qualitative analysis of biochemical data? We address this question in a case study by presenting the key concepts and experimental results that have led to our current understanding of cooperative oxygen binding by hemoglobin, the paradigm of structure function relations in multisubunit proteins. We conclude that the underlying simplicity of the two-state allosteric mechanism could not have been demonstrated without novel physical experiments and a rigorous quantitative analysis.

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Figure 1: Schematic structures of hemoglobin (adapted from ref.42).
Figure 2: MWC description of hemoglobin oxygenation.
Figure 3: Simplified schematic of the MWC/Perutz mechanism7,9,14.
Figure 4: Oxygen binding to a single crystal of hemoglobin in the T quaternary structure.
Figure 5: Kinetics of hemoglobin following nanosecond photodissociation of carbon monoxide complex40.
Figure 6: Schematic for ligand rebinding to a single subunit in the R quaternary structure40.

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Acknowledgements

We thank A. Szabo for numerous helpful discussions on the hemoglobin mechanism and for his comments on the manuscript. We also thank M. Brunori, P. Wolynes, and R. Zwanzig for helpful discussions, and G.L. Rossi for his generous support and collaboration in the single-crystal studies. This work was supported by a NATO Collaborative Research grant. This work was presented by W.A.E. at the Dahlem Workshop on "Simplicity and Complexity in Proteins and Nucleic Acids," Berlin, Germany, May 17–22, 1998 (eds Frauenfelder, H., Deisenhofer, J. & Wolynes, P.G.) Dahlem University Press (in the press).

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Correspondence to William A. Eaton.

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Eaton, W., Henry, E., Hofrichter, J. et al. Is cooperative oxygen binding by hemoglobin really understood?. Nat Struct Mol Biol 6, 351–358 (1999). https://doi.org/10.1038/7586

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