Conformational changes in soluble lens proteins during the development of senile nuclear cataract

Soluble crystallins were isolated, by gel filtration, from the nucleus and cortex of types I-IV cataractous lenses and neonatal lenses. Extinction coefficients were determined and used to calculate the proportion of the crystallins. alpha Crystallins were the major proteins in the cortex of the cataractous lens whereas beta crystallins predominate in the nucleus and in the neonatal lens. Electrophoretic and immunological data, indicated that there was very little soluble gamma crystallin in the cataractous tissue. Highly specific competitive radioimmunoassays were used to estimate the crystallin contents of the various extracts. Values obtained for the neonatal extracts agreed closely with those from gel filtration but, in general, the values found for the cataractous proteins were low. The immunological reactivity of beta crystallin decreased progressively with the development of nuclear colour whereas alpha crystallin reactivity decreased sharply with the onset of nuclear cataract (type II lens) and then partially recovered. No significant alterations were found in the micro-environments of tryptophan residues in any of the proteins indicating that there are no gross conformational changes in the soluble proteins during cataract development. It would appear that the losses of immunochemical reactivity are due to chemical and/or conformational alterations which are restricted to the surface of the protein molecules.