1IBE

DEOXY-HAEMOGLOBIN TRAPPED IN THE HIGH-AFFINITY (R) STATE

Summary for 1IBE

• Entry DOI: 10.2210/pdb1ibe/pdb
• Descriptor: HEMOGLOBIN (DEOXY), PROTOPORPHYRIN IX CONTAINING FE, ... (4 entities in total)
• Functional Keywords: heme, oxygen transport, respiratory protein, erythrocyte
• Biological source: Equus caballus (horse); More
• Total number of polymer chains: 2
• Total formula weight: 32387.53

Authors

Wilson, J.,Phillips, K.,Luisi, B. (deposition date: 1996-09-25, release date: 1996-12-23, Last modification date: 2024-02-07)

Primary citation

Wilson, J.,Phillips, K.,Luisi, B.
The crystal structure of horse deoxyhaemoglobin trapped in the high-affinity (R) state.
J.Mol.Biol., 264:743-756, 1996

PubMed Abstract: Co-operative oxygen binding by the vertebrate haemoglobins arises from an equilibrium between a quaternary structure with low affinity (T), favoured in the absence of ligand, and a high affinity form (R) adopted by the fully ligated protein. While R state haemoglobin has an oxygen affinity close to that of isolated subunits, the affinity of the T state is roughly 300-fold lower. The mechanism by which the T state restrains ligand binding, and the pathway of the quaternary transition, have been largely revealed by detailed crystallographic analyses of a number of haemoglobin molecules in the equilibrium states, as well as intermediate forms of the T state including partially ligated species. The ligation intermediates of the R state, however, have not been as well characterized structurally. We report here the crystal structure of one such intermediate species, namely, horse deoxyhaemoglobin in the R state, at 1.8 A resolution. While ligand binding in the T state may result in unfavourable stereochemistry in and around the haem-ligand complex, the more plastic R structure appears to accommodate equally well both liganded and ligand-free haem. Loss of ligand at the R state haem results in movements of the haem and shifts of the FG corners, which form characteristic intersubunit contacts that distinguish the quaternary states. The shifts are comparable in magnitude to the corresponding movements associated with de-ligation in the T state, although they differ in direction. These and other differences illustrate how the structural changes in the haem pocket are communicated to the subunit interfaces and how the movements that can occur in the R state may be impeded in the T state.

PubMed: 8980683
DOI: 10.1006/jmbi.1996.0674

Experimental method

X-RAY DIFFRACTION (1.8 Å)