Cleavage of amino acid residue(s) from the N-terminal region of alpha A- and alpha B-crystallins in human crystalline lens during aging

The current study reports for the first time a posttranslational modification at the N-terminal region of alpha A- and alpha B-crystallins in normal human lens. The posttranslational modification involves a loss of amino acid residues from the N-terminal region. We found three types of losses of N-terminal amino acid(s) from alpha-crystallin. One is the loss of the N-terminal amino acid residues 1-3 from alpha A-crystallin in aged lenses of the age 70 group. The other two modifications were found in alpha B-crystallin. One is the loss of Met(1) of the N-terminus and the other is the loss of 6 amino acids from the N-terminal region. These phenomena were observed in the lenses >40 age group. Recent studies suggest that the N-terminal region of alpha-crystallin may play a chaperone-like role at the molecular level. These losses of amino acids from the N-terminal region may affect this molecular chaperone-like activity as well as the transparent properties of the human lens. (C) 1997 Academic Press.