An electron density projection of a fiber like those in the previous picture of a sickled cell.
A model of the fiber with each hemoglobin molecule depicted as a sphere. The molecules are arranged on double strands. One double strand is shown in yellow. A fiber has seven double strands.
The fiber model rotates to provide an end-on view.
Which now shows a space filling model.
We zoom in to observe greater structural detail.
Red lines show how the molecules are paired.
There are contacts between double strands (red)...
...and within double strands (blue and green).
Zooming in on a single molecule shows the polypeptide chain. Contact regions between molecules are color coded.
Some mutant forms of hemoglobin affect fiber formation and some do not. We can test he model by seeing if those mutants that affect fiber formation are located at contacts and if those that do not are located away from contacts.
If a residue is purple then it affects fiber formation. If it is blue it does not. If the model is correct all of the purple residues would be in red, green, and blue parts of the molecule and all of the blue residues would be in the grey parts of the molecule.
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