Loss of the C-terminal serine residue from bovine beta B2-crystallin.
Electrospray mass spectrometric (ES-MS) examination of bovine beta-crystallins showed a significant component corresponding in mass to beta B2-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 beta B2-crystallin from foetal lenses and the proportion of the truncated form, as judged by ES-MS, was lower in beta-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 alpha A-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 beta B2-crystallin.
Kilby
G W
GW
Australian Cataract Research Foundation, University of Wollongong, NSW.
Carver
J A
JA
Zhu
J L
JL
Sheil
M M
MM
Truscott
R J
RJ
D000375:Aging / Q000502:physiology*; D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D003459:Crystallins / Q000737:chemistry*; D006801:Humans; D007908:Lens, Crystalline / Q000737:chemistry / Q000196:embryology; D013058:Mass Spectrometry / Q000379:methods; D010454:Peptide Termination Factors; D012694:Serine
D003459:Crystallins; D010454:Peptide Termination Factors; D012694:Serine