title: Age-related cleavages of crystallins in human lens cortical fiber cells generate a plethora of endogenous peptides and high molecular weight complexes.
abstract: Low molecular weight peptides derived from the breakdown of crystallins have been reported in adult human lenses. The proliferation of these LMW peptides coincides with the earliest stages of cataract formation, suggesting that the protein cleavages involved may contribute to the aggregation and insolubilization of crystallins. This study reports the identification of 238 endogenous LMW crystallin peptides from the cortical extracts of four human lenses representing young, middle and old-age human lenses. Analysis of the peptide terminal amino acids showed that Lys and Arg were situated at the C-terminus with significantly higher frequency compared to other residues, suggesting that trypsin-like proteolysis may be active in the lens cortical fiber cells. Selected reaction monitoring analysis of an endogenous αA-crystallin peptide (αA(57-65)) showed that the concentration of this peptide in the human lens increased gradually to middle age, after which the rate of αA(57-65) formation escalated significantly. Using 2D gel electrophoresis/nanoLC-ESI-MS/MS, 12 protein complexes of 40-150 kDa consisting of multiple crystallin components were characterized from the water soluble cortical extracts of an adult human lens. The detection of these protein complexes suggested the possibility of crystallin cross-linking, with these complexes potentially acting to stabilize degraded crystallins by sequestration into water soluble complexes.
authors.affiliation: Illawarra Health and Medical Research Institute, School of Biological Sciences, Faculty of Science, Medicine and Health, University of Wollongong, Wollongong, New South Wales, 2522, Australia.
authors.forename: Shih-Ping
authors.initials: SP
authors.lastname: Su
authors.affiliation: Australian Proteome Analysis Facility, Macquarie University, Sydney, New South Wales, 2109, Australia.
authors.forename: Xiaomin
authors.initials: X
authors.lastname: Song
authors.affiliation: Australian Proteome Analysis Facility, Macquarie University, Sydney, New South Wales, 2109, Australia.
authors.forename: Dylan
authors.initials: D
authors.lastname: Xavier
authors.affiliation: Illawarra Health and Medical Research Institute, School of Biological Sciences, Faculty of Science, Medicine and Health, University of Wollongong, Wollongong, New South Wales, 2522, Australia.
authors.forename: J Andrew
authors.initials: JA
authors.lastname: Aquilina
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D000595:Amino Acid Sequence; D002457:Cell Extracts; D003459:Crystallins / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D007908:Lens, Crystalline / Q000737:chemistry* / Q000166:cytology*; D008969:Molecular Sequence Data; D010455:Peptides / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism
chemical_list: D002457:Cell Extracts; D003459:Crystallins; D010455:Peptides
keywords: 2D gel electrophoresis; crystallin; endogenous peptides; lens aging; nanoLC-ESI-MS/MS; trypsin-like cleavage