Protein crystallization is mainly used for purification, storage and x-ray structure analysis, but it is also of significance in the biomedical field, as protein crystallization appears to be involved in the development and manifestation of certain human diseases. For example sickle cell anemia belongs to the type of protein condensation diseases in which the underlying pathology involves a loss of protein solubility. Furthermore, cataracts are usually considered a protein condensation disease associated with protein precipitation or possibly protein crystallization. Clues in lens physiology and biochemistry in normal as well as cataractous lenses led us to investigate cataracts from the standpoint of protein crystallization. We have focused on Hereditary Hyperferritinemia Cataract Syndrome (HHCS) as a model system. HHCS, which was first described fairly recently [1], is characterized by early onset of cataract formation. In HHCS the protein deposits that cause the lens to turn opaque were determined to be apoferritin crystals [2, 3].

We have investigated the influence of temperature and divalent cations, as well as the effect of the tissue origin of apoferritin, on the onset of crystal formation. Additionally, different additives and their potential ability to delay the onset of crystallization have been tested. The initial evidence supports an hypothesis that the additives modify protein solubility and therefore expand the domain of conditions under which the protein remains in solution.

Protein crystallization experiments were performed in vitro to determine the short-range protein-protein interactions and the physicochemical factors influencing them, such as temperature and nature of the divalent cation precipitant. Dilute protein-protein interactions in the liquid phase were evaluated by measuring the osmotic second virial coefficient of solutions via static light scattering (SLS). Correlations between the osmotic second virial coefficient and the protein crystallization or precipitation outcome were investigated. The possibility of using the osmotic second virial coefficient to establish the potential of protein precipitation or crystallization out of a biological fluid, hence the likelihood of disease to occur, will be discussed.

1. Girelli, D., et al., A linkage between hereditary hyperferritinaemia not related to iron overload and autosomal dominant congenital cataract. British journal of haematology, 1995. 90(4): p. 931-4.

2. Brooks, D.G., et al., Ferritin crystal cataracts in hereditary hyperferritinemia cataract syndrome. Investigative Ophthalmology & Visual Science, 2002. 43(4): p. 1121-1126.

3. Mumford, A.D., et al., The lens in hereditary hyperferritinaemia cataract syndrome contains crystalline deposits of L-ferritin. British Journal of Ophthalmology, 2000. 84(7): p. 697-700.