title: Elucidation of a novel polypeptide cross-link involving 3-hydroxykynurenine.
abstract: 3-Hydroxykynurenine, a metabolite of tryptophan, is a powerful antioxidant and neurotoxin. The neurotoxicity results from the oxidation of 3-hydroxykynurenine, and hydroxyl radicals, formed via H(2)O(2), may also be implicated [Okuda, S., Nishiyama, N., Saito, H. , and Katsuki, H. (1996) Proc. Natl. Acad. Sci. U.S.A. 93, 12553-12558]. Oxidation of o-aminophenols, such as 3-hydroxykynurenine, also results in the formation of highly reactive quinonimines. Thus, one possible consequence of 3-hydroxykynurenine oxidation may be covalent modification of cellular macromolecules. Such a process could contribute to the neurotoxicity and may potentially be important in other tissues, such as the human lens, where 3-hydroxykynurenine functions as a UV filter. In this work, we demonstrate that 3-hydroxykynurenine can bind to protein amino groups and, further, that under oxidative conditions, 3-hydroxykynurenine can function to cross-link polypeptide chains. The structure of the cross-linked moiety, using the peptide glycyllysine, has been elucidated. The cross-link, which is both colored and fluorescent, involves the peptide alpha-amino groups. Proteins modified by 3-hydroxykynurenine become colored and fluorescent as well as cross-linked. LC-MS studies indicate that the cross-link is also present in gamma-crystallin, following incubation of this lens protein in the presence of 3-hydroxykynurenine. Similar posttranslational modifications of lens proteins accompany cataract formation, and knowledge of the precise mode of reaction of 3-hydroxykynurenine with proteins will assist in determining if 3-hydroxykynurenine is involved in degenerative conditions in which oxidation of such aminophenols is implicated.
authors.affiliation: Australian Cataract Research Foundation, University of Wollongong, N. S.W., Australia.
authors.forename: J A
authors.initials: JA
authors.lastname: Aquilina
authors.forename: J A
authors.initials: JA
authors.lastname: Carver
authors.forename: R J
authors.initials: RJ
authors.lastname: Truscott
mesh_terms: D000818:Animals; D002417:Cattle; D003432:Cross-Linking Reagents / Q000737:chemistry / Q000378:metabolism; D003459:Crystallins / Q000737:chemistry / Q000378:metabolism; D004151:Dipeptides / Q000737:chemistry / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007737:Kynurenine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D013058:Mass Spectrometry; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000737:chemistry / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet
chemical_list: D003432:Cross-Linking Reagents; D003459:Crystallins; D004151:Dipeptides; D010455:Peptides; C005045:3-hydroxykynurenine; D007737:Kynurenine; C035809:glycyllysine