title: Covalent modification of epithelial fatty acid-binding protein by 4-hydroxynonenal in vitro and in vivo. Evidence for a role in antioxidant biology.
abstract: 4-Hydroxynonenal (4-HNE) is a cytotoxic alpha,beta-unsaturated acyl aldehyde that is naturally produced from lipid peroxidation and cleavage in response to oxidative stress and aging. Such reactive lipids covalently modify cellular target proteins, thereby affecting biological structure and function. Herein we report the identification of the epithelial fatty acid-binding protein (E-FABP) as a molecular target for 4-HNE modification both in vitro and in vivo. 4-HNE covalently modified (t(12) < 60 s) E-FABP in vitro, as revealed by a combination of matrix-assisted laser desorption ionization-time of flight mass spectrometry and immunochemical reactivity using antibodies directed to 4-HNE-protein conjugates. Identification of Cys-120 as the major site of modification was determined through tandem mass spectral sequencing of tryptic peptides, as well as analysis of E-FABP mutants C120A, C127A, and C120A/C127A. The in vitro modification of Cys-120 by 4-HNE was relatively insensitive to pH (6.4-8.4), and temperature (4-37 degrees C) but was markedly potentiated by noncovalently bound fatty acids. 4-HNE-modified E-FABP was more stable than unmodified E-FABP to chemical denaturation by guanidine hydrochloride, as assessed by changes in intrinsic tryptophan fluorescence. Analysis of soluble protein extracts from rat retina with antibodies directed to 4-HNE-protein conjugates revealed immunoreactivity with a 15-kDa protein that was identified by electrospray ionization and matrix-assisted laser desorption ionization-time of flight mass spectrometry as E-FABP. Evaluation of retinal pigment epithelial cell extracts derived from E-FABP null mice by two-dimensional gel electrophoresis using anti-4-HNE antibodies revealed increased modification in the null cells relative to those from wild type cells. These results indicate that E-FABP is a molecular target for 4-HNE modification and the hypothesis that E-FABP functions as an antioxidant protein by scavenging reactive lipids through covalent modification of Cys-120.
authors.affiliation: Department of Biochemistry, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: Assumpta
authors.initials: A
authors.lastname: Bennaars-Eiden
authors.forename: LeeAnn
authors.initials: L
authors.lastname: Higgins
authors.forename: Ann V
authors.initials: AV
authors.lastname: Hertzel
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Kapphahn
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Ferrington
authors.forename: David A
authors.initials: DA
authors.lastname: Bernlohr
mesh_terms: D000447:Aldehydes / Q000494:pharmacology*; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D002352:Carrier Proteins / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D003545:Cysteine; D004847:Epithelial Cells / Q000201:enzymology; D004926:Escherichia coli / Q000378:metabolism; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D019791:Guanidine; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D018384:Oxidative Stress / Q000502:physiology; D010446:Peptide Fragments / Q000737:chemistry; D011489:Protein Denaturation; D011994:Recombinant Proteins / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D000447:Aldehydes; D000975:Antioxidants; D002352:Carrier Proteins; C082667:Fabp5 protein, mouse; C086936:Fabp7 protein, mouse; C490174:Fabp7 protein, rat; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D010446:Peptide Fragments; D011994:Recombinant Proteins; D019791:Guanidine; C027576:4-hydroxy-2-nonenal; D003545:Cysteine