AGE-DEPENDENT CLEAVAGE AT THE C-TERMINAL REGION OF LENS BETA-B2 CRYSTALLIN

A previous study has demonstrated that in vivo, the peptide bonds at t he C-terminal region of the alpha-A crystallins were cleaved in an age -dependent manner, between the two hydroxyl-containing amino acids in the sequence -PS(T)S (Takemoto, 1995). Bovine beta B2 crystallin also contains the sequence PSS at its C-terminus. To determine if this spec ific site of cleavage occurred in other lens proteins besides alpha-A crystallin, beta B2 crystallin was prepared from total proteins of you ng versus adult bovine lens fiber cells. After cleavage by cyanogen br omide, the C-terminal fragments were characterized by mass spectrometr y. The results showed that peptide cleavage also occurred between the two hydroxyl-containing amino acids in the sequence -PSS of beta B2 cr ystallin from older fiber cells, demonstrating that age-dependent clea vage of this peptide bond occurs in multiple proteins of the aging len s. (C) 1995 Academic Press Limited