Loss of the C-terminal serine residue from bovine βB2-crystallin

Abstract

Electrospray mass spectrometric (ES-MS) examination of bovine β-crystallins showed a significant component corresponding in mass to βB2-crystallin less one serine residue. Tryptic digestion, followed by isolation and characterisation of the C-terminal peptide, demonstrated that this new species has arisen by the loss of the C-terminal serine residue. This phenomenon appears to be age-related since no truncation was detected in βB2-crystallin from foetal lenses and the proportion of the truncated form, as judged by ES-MS, was lower in β-crystallin isolated from calf lenses than that from the lenses of 3-year-old animals. This process therefore is similar to a recently reported loss of the C-terminal serine from αA-crystallin, which we have confirmed using ES-MS. Loss of a C-terminal serine from both crystallins may indicate the presence of carboxypeptidase-A-like activity in bovine lenses. ES-MS data provided no evidence for a significant degree of phosphorylation of βB2-crystallin. Show more