Age-related changes in human lens crystallins identified by two- dimensional electrophoresis and mass spectrometry

The purpose of this study was to identify the major protein components in adult human lenses and to analyse the specific age-related changes in these proteins using two-dimensional electrophoresis, Edman sequencing, and in conjunction with the data in the accompanying manuscript, mass spectrometry. The majority of changes in the two-dimensional electrophoretic pattern of lens proteins occurred prior to 17 years of age, and included a decrease in proteins migrating to the original positions of βB1, βB3, βA3, γC and γD, and the appearance of many new species with apparent molecular weights on two-dimensional electrophoretic gels similar to βB2 and βS, but having more acidic pIs. These proteins were identified as deamidated forms of βB1 and βA3/A1 missing portions of their N-terminal extensions. With the exception of αB, deamidation was detected in all crystallin species. These data indicated that a major fraction of the water-soluble protein of the adult human lens is composed of truncated βB1 and βA3/A1 crystallins, and that nearly all human crystallins, including the β-crystallins, are susceptible to deamidation. The results also provided the most detailed map to date of the identities of protein species on two-dimensional electrophoresis gels of adult human lenses.