Animation: A schematic view of the functional action of the oxygen transport maquette. The basic four alpha-helix bundle design (seen end-on, left, or in a side-view, right) has histidines (green pentagons) pointed towards the bundle interior to bind to either side of the iron atom in the middle of the planar heme (brown rectangle). One of these helices is under strain from the normally charged glutamate residues which prefer to be in the watery exterior of the bundle. This preference encourages dissociation of one histidine and frees the iron for ligation to a nearby oxygen molecule (pair of red dots).
Credit: Ronald L. Koder, PhD, et al. University of Pennsylvania School of Medicine; Nature
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