You can manipulate the structure directly by dragging with the mouse. Mouse drag down with Shift key to zoom. Try gestures on touch screen devices. Click on the links below the black box to see other useful views of the structure. Advanced users can select the Console from the function menu and directly enter JSmol commands.
The initial view shows all the hemes and the sidechains of His45 of the alpha chains. Interactions between His45s mediate the R to T transition.
This protein has a five-member alpha-helix barrel structure with a right-handed twist as observed in enzymes. See the discussion under the dihydrodipicolinate synthase animation. Like the enzymes, there is a need for constraint around the centre. This allows one binding site to do work on another. The oxygen binding sites also exchange energy (work) with the alpha chain His45 sidechains at the protein-protein interfaces through the constrained central region. In addition, hemoglobin has a negative catalytic effect in slowing down the autoxidation of oxyhemoglobin to methemoglobin and participates in the catalysed reduction of methemoglobin by other cell constituents. Both these processes probably depend on constraint.
The unusual elongated lobes of the monomers could well be an adaptation to the very low solubility of oxygen in water. It may be that oxygen is more soluble at the protein-water interface and the lobes serve as conduits between bulk water and the oxygen binding sites.
For further information about this protein, see the post of 13 August 2008 on nativeproteins.blogspot.com A link to the "Haemoglobin Revisited" poster was posted on 22 September 2008 and further comments posted on 30 May 2011 and 12 June 2011.
Or contact the author, Dr Don Vanselow at dvanselow@hotmail.com
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