Structural transitions upon ligand binding in a cooperative dimeric hemoglobin.
Comparison of the 2.4 angstrom resolution crystal structures of dimeric clam hemoglobin in the deoxygenated and carbon-monoxide liganded states shows how radically different the structural basis for cooperative oxygen binding is from that operative in mammalian hemoglobins. Heme groups are in direct communication across a novel subunit interface formed by the E and F helices. The conformational changes at this interface that accompany ligand binding are more dramatic at a tertiary level but more subtle at a quaternary level than those in mammalian hemoglobins. These findings suggest a cooperative mechanism that links ligation at one subunit with potentiation of affinity at the second subunit.
Royer
W E
WE
Howard Hughes Medical Institute, Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032.
Hendrickson
W A
WA
Chiancone
E
E
D000595:Amino Acid Sequence; D000818:Animals; D002263:Carboxyhemoglobin / Q000378:metabolism; D006454:Hemoglobins / Q000378:metabolism*; D008024:Ligands; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008974:Mollusca; D011487:Protein Conformation
D006454:Hemoglobins; D008024:Ligands; D046911:Macromolecular Substances; D002263:Carboxyhemoglobin