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 the 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 specific site of cleavage occurred in other lens proteins besides alpha-A crystallin, beta B2 crystallin was prepared from total proteins of young versus adult bovine lens fiber cells. After cleavage by cyanogen bromide, the C-terminal fragments were characterized by mass spectrometry. The results showed that peptide cleavage also occurred between the two hydroxyl-containing amino acids in the sequence -PSS of beta B2 crystallin from older fiber cells, demonstrating that age-dependent cleavage of this peptide bond occurs in multiple proteins of the aging lens.