Sickle hemoglobin fibers - self assembly, interactions, growth and depolymerisation

It has been known for many years that hemoglobin can aggregate into 'crosslinked gels' within the red blood cells of carriers of the defective sickle hemoglobin gene. However it is only relatively recently that we have started to understand the properties of the individual fibers that make up this gel. These fibers exhibit a variety of striking properties. They have preferred diameters that are larger than the size of the single monomer, and may therefore not be set by this length scale alone. Parallel fibers 'zipper' together into bundles due to interactions that we have been able to quantify rather precisely. The fiber growth rate constants can be sufficient to distort the shape of the red cell membrane and the fiber. Finally the fiber has a novel depolymerisation mechanism that involves two rate constants giving rise to a time scale for complete depolymerisation that is insensitive to the initial fiber length.