Three-dimensional reconstruction of the fibres of sickle cell haemoglobin.

Three-dimensional reconstruction of electron micrographs of the 20-nm diameter fibres of HbS reveals an inner helical core of four strands surrounded by an outer helix of 10 strands to give a total of 14 strands. The strands are arranged with roughly hexagonal packing to produce an unusual helical structure which features a variety of intermolecular contacts and a non-circular cross section.