Photo-oxidation of proteins and its role in cataractogenesis

https://doi.org/10.1016/S1011-1344(01)00208-1Get rights and content

Abstract

Proteins comprise approximately 68% of the dry weight of cells and tissues and are therefore potentially major targets for photo-oxidation. Two major types of processes can occur with proteins. The first of these involves direct photo-oxidation arising from the absorption of UV radiation by the protein, or bound chromophore groups, thereby generating excited states (singlet or triplets) or radicals via photo-ionisation. The second major process involves indirect oxidation of the protein via the formation and subsequent reactions of singlet oxygen generated by the transfer of energy to ground state (triplet) molecular oxygen by either protein-bound, or other, chromophores. The basic principles behind these mechanisms of photo-oxidation of amino acids, peptides and proteins and the potential selectivity of damage are discussed. Emphasis is placed primarily on the intermediates that are generated on amino acids and proteins, and the subsequent reactions of these species, and not the identity or chemistry of the sensitizer itself, unless the sensitizing group is itself intrinsic to the protein. A particular system is then discussed – the cataractous lens – where UV photo-oxidation may play a role in the aetiology of the disease, and tryptophan-derived metabolites act as UV filters.

Introduction

Proteins are major targets for photo-oxidation within cells due to their high abundance, the presence of endogenous chromophores within the protein structure (both amino acid side-chains and bound prosthetic groups such as flavins and heme), their ability to bind exogenous chromophoric materials, and their rapid rates of reaction with other excited state species. Photo-oxidation of proteins has been traditionally been defined as occurring via two major routes. The first of these is direct photo-oxidation arising from the absorption of UV radiation by the protein structure (primarily side-chains), or bound chromophores, thereby generating excited state species (singlet or triplets) or radicals as a result of photo-ionisation; these mechanisms are often referred to as Type 1 processes. The second major process involves indirect oxidation of the protein via the formation and subsequent reactions of singlet oxygen (molecular oxygen in its first excited singlet state, 1Δg O2 or 1O2) generated by the transfer of energy to ground state (triplet) molecular oxygen by either protein-bound, or other chromophores; these reactions are often referred to as Type 2 processes.

Section snippets

Ground state absorption spectra of amino acids, peptides and proteins

Direct oxidation of amino acids, peptides and proteins by UV light is only a significant process if the incident light is absorbed by the protein. For most proteins without bound (covalent or non-covalent) co-factors or prosthetic groups this only occurs with light with λ≤ca. 320 nm. The major chromophoric amino acids present in proteins are tryptophan (Trp), tyrosine (Tyr), phenylalanine (Phe), histidine (His), cysteine (Cys) and cystine; the UV spectra of these amino acids are given in Ref.

Formation and reactions of singlet states

The absorption of UV light by Trp, Tyr, His, Phe, Cys and cystine can give both excited state species and radicals via photo-ionisation (reviewed in Refs. [1], [3]). The relative energies of the short-lived first excited singlet states decrease in the order: Phe>Tyr>Trp [3], which can result in rapid energy transfer from Phe and Tyr to Trp. This is the reason why the fluorescence spectra of most proteins is often dominated by that of Trp. All three of these amino acids show broad featureless

Indirect (Type 2) photo-oxidation: formation and reactions of singlet oxygen

Photolysis of aromatic compounds (e.g., naphthalene and anthracene derivatives) or conjugated alkenes (e.g., porphyrins, a wide variety of dye molecules) generates excited states that can undergo rapid energy transfer with O2. Such reactions usually generate the first excited singlet state (1ΔgO2) of molecular oxygen. This state, which has both electrons in the same molecular orbital with paired spins, is formed readily, being only ca. 94 kJ mol−1 above the ground triplet state (3Σ), and has a

Physical and chemical consequences of photo-oxidation of proteins

Von Tappeiner in 1903, first established that exposure of enzymes to a photosensitizer in the presence of air and light resulted in loss of enzymatic or functional activity [57]. In the majority of studies on the 1O2-mediated oxidation of proteins the products have not been elucidated in a quantitative manner, though a number of studies have reported the formation of N-formylkynurenine and kynurenine from Trp [49], Met sulphoxide from Met [58], [59], and cystine from Cys [26]. In a number of

Human studies

The lens of the eye is designed to transmit light. Since we know, often from personal experience, e.g., sunburn, that solar radiation has the potential to damage biological tissues, it is but a short step to conclude that exposure to UV radiation over a lifetime may be responsible for the most common form of blindness: age related cataract. This hypothesis becomes more tenable when one appreciates that proteins in the bulk of the lens do not turn over; thus proteins in the centre of the lens

Acknowledgements

The authors would like to thank the Australian Research Council, the National Health and Medical Research Council, and the Wellcome Trust for financial support, and the members of the Australian Cataract Research Foundation who have been involved in some of the work reported here.

References (105)

  • H.R. Shen et al.

    Photodynamic crosslinking of proteins. I. Model studies using histidine- and lysine-containing N-(2-hydroxypropyl)methacrylamide copolymers

    J. Photochem. Photobiol. B: Biol.

    (1996)
  • H.R. Shen et al.

    Photodynamic cross-linking of proteins – IV. Nature of the His–His bond(s) formed in the rose bengal-photosensitized cross-linking of N-benzoyl-l-histidine

    J. Photochem. Photobiol. A

    (2000)
  • M. Linetsky et al.

    The aggregation in human lens proteins blocks the scavenging of UVA-generated singlet oxygen by ascorbic acid and glutathione

    Arch. Biochem. Biophys.

    (1998)
  • B.J. Ortwerth et al.

    UVA irradiation of human lens proteins produces residual oxidation of ascorbic acid even in the presence of high levels of glutathione

    Arch. Biochem. Biophys.

    (1998)
  • H. Shen et al.

    Photodynamic cross-linking of proteins. V. Nature of the tyrosine–tyrosine bonds formed in the FMN-sensitized intermolecular cross-linking of N-acetyl-l-tyrosine

    J. Photochem. Photobiol. A

    (2000)
  • T.M. Dubbelman et al.

    Temperature dependence of photodynamic red cell membrane damage

    Biochim. Biophys. Acta

    (1980)
  • H.R. Shen et al.

    Photodynamic crosslinking of proteins. II. Photocrosslinking of a model protein-ribonuclease A

    J. Photochem. Photobiol. B: Biol.

    (1996)
  • J.A. Silvester et al.

    Photodynamically-generated bovine serum albumin radicals: evidence for damage transfer and oxidation at cysteine and tryptophan residues

    Free Radic. Biol. Med.

    (1998)
  • J.A. Silvester et al.

    Protein hydroperoxides and carbonyl groups generated by porphyrin-induced photo-oxidation of bovine serum albumin

    Arch. Biochem. Biophys.

    (1998)
  • H.S. Yim et al.

    Free radicals generated during the glycation reaction of amino acids by methylglyoxal. A model study of protein-cross-linked free radicals

    J. Biol. Chem.

    (1995)
  • C. Prinsze et al.

    Protein damage, induced by small amounts of photodynamically generated singlet oxygen or hydroxyl radicals

    Biochim. Biophys. Acta

    (1990)
  • E. Silva et al.

    Lysozyme photo-oxidation by singlet oxygen: properties of the partially inactivated enzyme

    J. Photochem. Photobiol. B: Biol.

    (2000)
  • S. Zigman et al.

    The nature and properties of squirrel lens yellow pigment

    Exp. Eye Res.

    (1988)
  • A. Thorpe et al.

    Kynurenine identified as the short-wave absorbing lens pigment in the deep-sea fish Sylephorus cordatus

    Exp. Eye Res.

    (1992)
  • O. Takikawa et al.

    Indoleamine 2,3-dioxygenase in the human lens, the first enzyme in the synthesis of UV filters

    Exp. Eye Res.

    (2001)
  • A. Stewart et al.

    Pyridine nucleotides in normal and cataractous human lenses

    Exp. Eye Res.

    (1984)
  • B. Garner et al.

    Identification of glutathionyl-3-hydroxykynurenine glucoside as a novel fluorophore associated with aging of the human lens

    J. Biol. Chem.

    (1999)
  • B.D. Hood et al.

    Human lens coloration and aging. Evidence for crystallin modification by the major ultraviolet filter, 3-hydroxy-kynurenine O-beta-d-glucoside

    J. Biol. Chem.

    (1999)
  • R.V. Bensasson et al.

    Pulse Radiolysis and Flash Photolysis: Contributions to the Chemistry of Biology and Medicine

    (1983)
  • R.V. Bensasson et al.

    Excited States and Free Radicals in Biology and Medicine

    (1993)
  • R.S. Becker

    Theory and Interpretation of Fluorescence and Phosphorescence

    (1969)
  • C. Pigault et al.

    Influence of the location of tryptophanyl residues in proteins on their photosensitivity

    Photochem. Photobiol.

    (1984)
  • D.V. Bent et al.

    Excited state chemistry of aromatic amino acids and related peptides. II. Phenylalanine

    J. Phys. Chem.

    (1975)
  • D.V. Bent et al.

    Excited state chemistry of aromatic amino acids and related peptides. I. Tyrosine

    J. Phys. Chem.

    (1975)
  • D.V. Bent et al.

    Excited state chemistry of aromatic amino acids and related peptides. III. Tryptophan

    J. Phys. Chem.

    (1975)
  • S.P. McGlynn et al.

    Molecular Spectroscopy of the Triplet State

    (1969)
  • D. Creed

    The photophysics and photochemistry of the near-UV absorbing amino acids. I. Tryptophan and its simple derivatives

    Photochem. Photobiol.

    (1984)
  • D. Creed

    The photophysics and photochemistry of the near-UV absorbing amino acids. II. Tyrosine and its simple derivatives

    Photochem. Photobiol.

    (1984)
  • M.Z. Hoffman et al.

    One-electron reduction of the disulphide linkage in aqueous solution. Formation, protonation and decay kinetics of the RSSR radical

    J. Am. Chem. Soc.

    (1972)
  • M.J. Davies et al.

    Free radical reactions. Fragmentation and rearrangements in aqueous solution

    Adv. Detailed React. Mech.

    (1991)
  • M.J. Davies et al.

    Radical-Mediated Protein Oxidation: From Chemistry To Medicine

    (1997)
  • J.D. Spikes et al.

    Photodynamic crosslinking of proteins. III. Kinetics of the FMN- and rose bengal-sensitized photooxidation and intermolecular crosslinking of model tyrosine-containing N-(2-hydroxypropyl)methacrylamide copolymers

    Photochem. Photobiol.

    (1999)
  • D. Creed

    The photophysics and photochemistry of the near-UV absorbing amino acids. III. Cystine and its simple derivatives

    Photochem. Photobiol.

    (1984)
  • E.J. Hart et al.

    The Hydrated Electron

    (1970)
  • W.M. Garrison

    Reaction mechanisms in the radiolysis of peptides, polypeptides, and proteins

    Chem. Rev.

    (1987)
  • C. von Sonntag

    The Chemical Basis of Radiation Biology

    (1987)
  • R.C. Straight et al.

    Photosensitized oxidation of biomolecules

  • B. Monroe

    Singlet oxygen in solution: lifetimes and reaction rate constants

  • F. Wilkinson et al.

    Rate constants for the decay and reactions of the lowest electronically excited state of molecular oxygen in solution. An expanded and revised compilation

    J. Phys. Chem. Ref. Data

    (1995)
  • I.B.C. Matheson et al.

    The quenching of singlet oxygen by amino acids and proteins

    Photochem. Photobiol.

    (1975)
  • Cited by (389)

    • Polymers in cancer research and clinical oncology

      2023, Handbook of Polymers in Medicine
    • Effect of UV-LED irradiation processing on pectolytic activity and quality in tomato (Solanum lycopersicum) juice

      2022, Innovative Food Science and Emerging Technologies
      Citation Excerpt :

      In addition, enzymes have the additional ability to bind exogenous chromophores and react with other species in the excited state. Consequently, a change in enzymatic properties is generated due to backbone fragmentation, cross-linkage formation and oxidation of the side chains (Davies, 2003; Davies & Truscott, 2001; Manzocco, Panozzo, & Nicoli, 2013). In contrast, heat treatments that are greater than the optimum temperature generate an exponential decrease in enzymatic activity due to enzyme denaturation, suggesting first-order inactivation kinetics (Moens, De Laet, Van Ceunebroeck, Van Loey, & Hendrickx, 2021).

    View all citing articles on Scopus
    View full text