Allosteric action in real time: time-resolved crystallographic studies of a cooperative dimeric hemoglobin

UMMS Affiliation

Department of Biochemistry and Molecular Pharmacology



Document Type



Allosteric Regulation; Crystallography, X-Ray; Dimerization; Hemoglobins; Humans; Ligands; Models, Molecular; *Protein Structure, Quaternary; Protein Subunits; Scapharca; Time Factors; Water; X-Ray Diffraction


Life Sciences | Medicine and Health Sciences


Protein allostery provides mechanisms for regulation of biological function at the molecular level. We present here an investigation of global, ligand-induced allosteric transition in a protein by time-resolved x-ray diffraction. The study provides a view of structural changes in single crystals of Scapharca dimeric hemoglobin as they proceed in real time, from 5 ns to 80 micros after ligand photodissociation. A tertiary intermediate structure forms rapidly (<5 >ns) as the protein responds to the presence of an unliganded heme within each R-state protein subunit, with key structural changes observed in the heme groups, neighboring residues, and interface water molecules. This intermediate lays a foundation for the concerted tertiary and quaternary structural changes that occur on a microsecond time scale and are associated with the transition to a low-affinity T-state structure. Reversal of these changes shows a considerable lag as a T-like structure persists well after ligand rebinding, suggesting a slow T-to-R transition.

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Citation: Proc Natl Acad Sci U S A. 2006 May 16;103(20):7649-54. Epub 2006 May 9. Link to article on publisher's site

DOI of Published Version


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Link to Article in PubMed

Journal Title

Proceedings of the National Academy of Sciences of the United States of America

PubMed ID