Sequence analysis of βA3, βB3, and βA4 crystallins completes the identification of the major proteins in young human lens

A combination of Edman sequence analysis and mass spectrometry identified the major proteins of the young human lens as αA, αB, αA1, αA3, βA4, βB1, βB2, βB3, γS, γC, and γD-crystallins and mapped their positions on two-dimensional electrophoretic gels. The primary structures of human βA1, βA3, βA4, and βB3-crystallin subunits were predicted by determining cDNA sequences. Mass spectrometric analyses of each intact protein as well as the peptides from trypsin-digested proteins confirmed the predicted amino acid sequences and detected a partially degraded form of βA3/A1 missing either 22 or 4 amino acid residues from its N-terminal extension. These studies were a prerequisite for future studies to determine how human lens proteins are altered during aging and cataract formation.