example page for haemoglobinexample page for haemoglobin
Cooperative binding of oxygen by haemoglobinCooperative binding of oxygen by haemoglobin
The cooperative binding of oxygen by haemoglobin (pdb entry 1a00) results from restraints on in the T state. The unfavourable interactions made by the ligands at the haems destabilise the T state and favour the high affinity R state. The T <==> R equilibrium leads, in the presence of a ligand, to a rapid increase in the R state population and therefore generates cooperative binding. There is now considerable understanding of this phenomenon, but the interactions that reduce ligand affinity in the T state have not yet been fully explored, owing to the difficulties in preparing T state haemoglobin crystals in which all the subunits are oxygenated. A protocol has been developed to oxygenate deoxy T state adult human haemoglobin (HbA) crystals in air at 4 C at all four haems without significant loss of crystalline order. The X-ray crystal structure, determined to 2.1 A spacing, shows significant changes in the alpha and beta haem pockets as well as changes at the alpha(1)beta(2) interface in the direction of the R quaternary structure. Most of the shifts and deviations from deoxy T state HbA are similar to, but larger than, those previously observed in the T state met and other partially liganded T state forms. They provide clear evidence of haem-haem interaction in the T state. ‘[1]’.
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- ↑ Kavanaugh JS, Weydert JA, Rogers PH, Arnone A. High-resolution crystal structures of human hemoglobin with mutations at tryptophan 37beta: structural basis for a high-affinity T-state,. Biochemistry. 1998 Mar 31;37(13):4358-73. PMID:9521756 doi:http://dx.doi.org/10.1021/bi9708702