Motion in Hemoglobin (Hb) [hb]

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Classification Known Subunit Motion, Involving Allostery [S-a-2]

Structures 1HHO Conformation 3 [ PartsList ] 2HCO Conformation 2 [ PartsList ] 4HHB Conformation 1 [ PartsList ]

Description Hemoglobin is a tetramer containing 2 copies of 2 (slightly) different subunits (alpha and beta). When oxygen binds to the deoxy form (the T-state), the heme ring slightly flattens. This causes one helix (EF turn, F helix, FG turn) to move, and this, in turn, destabilizes salt bridges between this helix and a helix on another subunit. A new inter-subunit salt bridge configuration is formed (with in total fewer bridges). This switch of configurations at the subunit interface causes one pair of subunits (e.g. alpha-1 and beta-1) to rotate 15 degrees and translate 0.8 A relative to the other pair (producing the high-affinity R-state). This in, in turn, affects the interactions about the heme in other subunits, giving rise to cooperative oxygen binding.

Particular values describing motion Experimental Methods = x (Traditional x-ray) Creation Date = 19970822 Modification Date = 19970822

References G Fermi, M F Perutz, B Shaanan and R Fourme (1984). the crystal structure of human deoxyhaemoglobin at1.74 Å resolution. J. Mol. Biol. 175: 159-174. [Medline info for 6161375] L Stryer (1995). Biochemistry. New York, W H Freeman and Company. [Medline info for 6161375] J Baldwin and C Chothia (1979). Haemoglobin. The structural changes related to ligand binding and its allosteric mechanism. J. Mol. Biol. 129: 175-220. [Medline info for 6161375] M Perutz (1978). Hemoglobin structure and respiratory transport. Sci. Am. 239: 92-125. [Medline info for 6161375] M F Perutz (1989). Mechanisms of cooperativity and allosteric regulation in proteins. Quart. Rev. Biophys. 22: 139-237. [Medline info for 6161375]

Data and Graphics Graphic-1 General figure of the folding topology in the globins. (This is actually myoglobin. Hemoglobin does not have the D helix!)

GO terms associated with structures Molecular function oxygen binding, binding Cellular component hemoglobin complex Biological process transport, oxygen transport

Morphs

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Best representative Morph Morph name Structure #1 Structure #2 Residues [ ] [ ]

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Copyright 1995-2005 M. Gerstein, W. Krebs, S. Flores, N. Echols, and others
Email: Mark.Gerstein _at_ yale.edu