BIOPHYSICAL INVESTIGATIONS OF GAMMA CRYSTALLINS

超过50%的美国人在50岁以上

In excess of 50% of the population of the United States over 50 years of age has some form of cataract. Typical treatment for cataractous lenses involves their surgical removal followed by implantation of a fixed focus lens. In mammalian lenses, the core of the lens consists of a group of water soluble proteins termed gamma-crystallins. This family of proteins is monomeric with a molecular weight of approximately 20,000 daltons. There is a high degree of both sequence and structural homology present between the gamma-crystallins of different mammals and, for convenience, the gamma- crystallins from bovine calves are usually studied. The gamma-crystallins are named I - IV as a result of their elution profiles on a sulphopropyl column. There is selective synthesis of the individual gamma-crystallins with gamma-IV predominantly synthesized during foetal development. If a lens from a young mammal is cooled to 4oC, the lens becomes opaque. This opacity clears upon warming of the lens. This phenomenon is known as "cold cataract" and involves "cryoprecipitation at physiological concentrations. It is known that agents that increase the temperature at which these "cold cataracts" form, induce cataract formation in the whole lens. Conversely, agents that reduce the temperature of cold cataract formation can be used to clear chemically induced cataracts. It is therefore important to further characterize the biophysical behavior of these proteins. This study will compare and contrast the biophysical behavior of individual gamma-crystallins fractions. We will probe surface characteristics of these proteins in particular their interaction with water, investigate their thermal denaturation processes using both thermal analytical and spectroscopic techniques, and, investigate the enegetics involved during their cryoprecipitation.