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| - | == | + | ==example page for haemoglobin == |
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| - | + | ==Cooperative binding of oxygen by haemoglobin== | |
| - | + | <StructureSection load='1a00' size='300' side='right' caption='HUMAN BETA GLOBIN (PDB entry [[1a00]])' scene=''></StructureSection> | |
| - | + | The cooperative binding of oxygen by '''haemoglobin''' (pdb entry [[1a00]]) results from restraints on <scene name='60/609833/1/3'>heme</scene> 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. ‘<ref>PMID:9521756</ref>’. | |
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| - | + | =references== | |
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Current revision
example page for haemoglobin
Cooperative binding of oxygen by haemoglobin
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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]’. </structuresction>
references=
- ↑ 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
