Direct approach to identification, at the molecular level, of modified proteins in human nuclear cataractous lenses: beta-crystallin is a component of the urea-insoluble protein fraction.

Abstract

In an effort to elucidate the molecular changes which take place in the human lens with the onset of nuclear cataract, the urea-insoluble protein fraction, solubilized with dithiothreitol, was digested with trypsin. Tryptic peptides separated by HPLC, were examined by both mass spectrometry and Edman degradation. A pentapeptide Gly-Glu-Tyr-Pro-Arg which is contained within the beta-crystallin sequence was isolated. This finding provides direct evidence that beta-crystallin is present in the urea-insoluble protein fraction which is known to be characteristic of human nuclear cataract lenses.