Reversible binding of kynurenine to lens proteins: Potential protection by glutathione in young lenses

Nicole R. Parker, Anastasia Korlimbinis, Joanne F. Jamie, Michael J. Davies, Roger J W Truscott

Research output: Contribution to journalArticleResearchpeer-review

Abstract

PURPOSE. Human ultraviolet light (UV) filters, such as kynurenine (Kyn), readily deaminate to reactive unsaturated ketones that covalently modify proteins in older human lenses. The aim of this study was to examine in vitro rates of formation and decomposition of the three major Kyn-amino acid adducts and possible consequences for the lens. METHODS. The t-Boc-protected Kyn-His, Kyn-Lys, and Kyn-Cys adducts and Kyn-Cys were synthesized from the corresponding amino acids and Kyn. Calf lens proteins were modified with Kyn by incubation at pH 7. Stability and competition studies of the adducts were conducted under physiological conditions. Kyn-amino acids and their decomposition products were quantified using HPLC. RESULTS. At physiological pH, Kyn-Cys adducts formed more rapidly than either Lys or His adducts, but they also decomposed readily. By contrast, His adducts were stable. Cysteine (Cys) residues in β-crystallins were major sites of modification. The Kyn moiety, initially bound to Cys residues, was found to transfer to other amino acids. Glutathione promoted the breakdown of Kyn-Cys. CONCLUSIONS. These data may help explain why proteins in young lenses are not modified by UV filters in situ. The initial phase of the modification of proteins in the human lens by UV filters may be a dynamic process. In lenses, Cys residues of crystalline modify preferentially, but these adducts also decompose to release deaminated Kyn. This can then potentially react with other amino acids. Glutathione, which is present in high concentrations in the lenses of young people, may play a vital role in keeping proteins free from modification by intercepting reactive deaminated kynurenines formed by the spontaneous breakdown of free UV filters, promoting the decomposition of Kyn-Cys residues, and sequestering the unsaturated ketones once they are released from modified proteins.

LanguageEnglish
Pages3705-3713
Number of pages9
JournalInvestigative Ophthalmology and Visual Science
Volume48
Issue number8
DOIs
Publication statusPublished - Aug 2007

Fingerprint

Kynurenine
Crystallins
Lenses
Glutathione
Cysteine
Ultraviolet Rays
Amino Acids
Proteins
Ketones
beta-Crystallins

Cite this

Parker, Nicole R. ; Korlimbinis, Anastasia ; Jamie, Joanne F. ; Davies, Michael J. ; Truscott, Roger J W. / Reversible binding of kynurenine to lens proteins : Potential protection by glutathione in young lenses. In: Investigative Ophthalmology and Visual Science. 2007 ; Vol. 48, No. 8. pp. 3705-3713.
@article{930a2c8038934080b06df58b89743654,
title = "Reversible binding of kynurenine to lens proteins: Potential protection by glutathione in young lenses",
abstract = "PURPOSE. Human ultraviolet light (UV) filters, such as kynurenine (Kyn), readily deaminate to reactive unsaturated ketones that covalently modify proteins in older human lenses. The aim of this study was to examine in vitro rates of formation and decomposition of the three major Kyn-amino acid adducts and possible consequences for the lens. METHODS. The t-Boc-protected Kyn-His, Kyn-Lys, and Kyn-Cys adducts and Kyn-Cys were synthesized from the corresponding amino acids and Kyn. Calf lens proteins were modified with Kyn by incubation at pH 7. Stability and competition studies of the adducts were conducted under physiological conditions. Kyn-amino acids and their decomposition products were quantified using HPLC. RESULTS. At physiological pH, Kyn-Cys adducts formed more rapidly than either Lys or His adducts, but they also decomposed readily. By contrast, His adducts were stable. Cysteine (Cys) residues in β-crystallins were major sites of modification. The Kyn moiety, initially bound to Cys residues, was found to transfer to other amino acids. Glutathione promoted the breakdown of Kyn-Cys. CONCLUSIONS. These data may help explain why proteins in young lenses are not modified by UV filters in situ. The initial phase of the modification of proteins in the human lens by UV filters may be a dynamic process. In lenses, Cys residues of crystalline modify preferentially, but these adducts also decompose to release deaminated Kyn. This can then potentially react with other amino acids. Glutathione, which is present in high concentrations in the lenses of young people, may play a vital role in keeping proteins free from modification by intercepting reactive deaminated kynurenines formed by the spontaneous breakdown of free UV filters, promoting the decomposition of Kyn-Cys residues, and sequestering the unsaturated ketones once they are released from modified proteins.",
author = "Parker, {Nicole R.} and Anastasia Korlimbinis and Jamie, {Joanne F.} and Davies, {Michael J.} and Truscott, {Roger J W}",
year = "2007",
month = "8",
doi = "10.1167/iovs.06-1061",
language = "English",
volume = "48",
pages = "3705--3713",
journal = "Investigative Ophthalmology and Visual Science",
issn = "0146-0404",
publisher = "Association for Research in Vision and Ophthalmology",
number = "8",

}

Reversible binding of kynurenine to lens proteins : Potential protection by glutathione in young lenses. / Parker, Nicole R.; Korlimbinis, Anastasia; Jamie, Joanne F.; Davies, Michael J.; Truscott, Roger J W.

In: Investigative Ophthalmology and Visual Science, Vol. 48, No. 8, 08.2007, p. 3705-3713.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - Reversible binding of kynurenine to lens proteins

T2 - Investigative Ophthalmology and Visual Science

AU - Parker, Nicole R.

AU - Korlimbinis, Anastasia

AU - Jamie, Joanne F.

AU - Davies, Michael J.

AU - Truscott, Roger J W

PY - 2007/8

Y1 - 2007/8

N2 - PURPOSE. Human ultraviolet light (UV) filters, such as kynurenine (Kyn), readily deaminate to reactive unsaturated ketones that covalently modify proteins in older human lenses. The aim of this study was to examine in vitro rates of formation and decomposition of the three major Kyn-amino acid adducts and possible consequences for the lens. METHODS. The t-Boc-protected Kyn-His, Kyn-Lys, and Kyn-Cys adducts and Kyn-Cys were synthesized from the corresponding amino acids and Kyn. Calf lens proteins were modified with Kyn by incubation at pH 7. Stability and competition studies of the adducts were conducted under physiological conditions. Kyn-amino acids and their decomposition products were quantified using HPLC. RESULTS. At physiological pH, Kyn-Cys adducts formed more rapidly than either Lys or His adducts, but they also decomposed readily. By contrast, His adducts were stable. Cysteine (Cys) residues in β-crystallins were major sites of modification. The Kyn moiety, initially bound to Cys residues, was found to transfer to other amino acids. Glutathione promoted the breakdown of Kyn-Cys. CONCLUSIONS. These data may help explain why proteins in young lenses are not modified by UV filters in situ. The initial phase of the modification of proteins in the human lens by UV filters may be a dynamic process. In lenses, Cys residues of crystalline modify preferentially, but these adducts also decompose to release deaminated Kyn. This can then potentially react with other amino acids. Glutathione, which is present in high concentrations in the lenses of young people, may play a vital role in keeping proteins free from modification by intercepting reactive deaminated kynurenines formed by the spontaneous breakdown of free UV filters, promoting the decomposition of Kyn-Cys residues, and sequestering the unsaturated ketones once they are released from modified proteins.

AB - PURPOSE. Human ultraviolet light (UV) filters, such as kynurenine (Kyn), readily deaminate to reactive unsaturated ketones that covalently modify proteins in older human lenses. The aim of this study was to examine in vitro rates of formation and decomposition of the three major Kyn-amino acid adducts and possible consequences for the lens. METHODS. The t-Boc-protected Kyn-His, Kyn-Lys, and Kyn-Cys adducts and Kyn-Cys were synthesized from the corresponding amino acids and Kyn. Calf lens proteins were modified with Kyn by incubation at pH 7. Stability and competition studies of the adducts were conducted under physiological conditions. Kyn-amino acids and their decomposition products were quantified using HPLC. RESULTS. At physiological pH, Kyn-Cys adducts formed more rapidly than either Lys or His adducts, but they also decomposed readily. By contrast, His adducts were stable. Cysteine (Cys) residues in β-crystallins were major sites of modification. The Kyn moiety, initially bound to Cys residues, was found to transfer to other amino acids. Glutathione promoted the breakdown of Kyn-Cys. CONCLUSIONS. These data may help explain why proteins in young lenses are not modified by UV filters in situ. The initial phase of the modification of proteins in the human lens by UV filters may be a dynamic process. In lenses, Cys residues of crystalline modify preferentially, but these adducts also decompose to release deaminated Kyn. This can then potentially react with other amino acids. Glutathione, which is present in high concentrations in the lenses of young people, may play a vital role in keeping proteins free from modification by intercepting reactive deaminated kynurenines formed by the spontaneous breakdown of free UV filters, promoting the decomposition of Kyn-Cys residues, and sequestering the unsaturated ketones once they are released from modified proteins.

UR - http://www.scopus.com/inward/record.url?scp=34648817048&partnerID=8YFLogxK

U2 - 10.1167/iovs.06-1061

DO - 10.1167/iovs.06-1061

M3 - Article

VL - 48

SP - 3705

EP - 3713

JO - Investigative Ophthalmology and Visual Science

JF - Investigative Ophthalmology and Visual Science

SN - 0146-0404

IS - 8

ER -