Dataset Information

Organophosphorus pesticides catalyze protein crosslinking

ABSTRACT: Exposure to organophosphorus pesticides (OP) can have chronic adverse effects that are independent of inhibition of acetylcholinesterase, the classic target for acute OP toxicity. In pure proteins, the organophosphorus pesticide chlorpyrifos oxon induces a crosslink between lysine and glutamate (or aspartate) with loss of water. Tubulin is particularly sensitive to OP-induced crosslinking. Our goal was to explore OP-induced crosslinking in a complex protein sample, MAP-rich tubulin from Sus scrofa, and to test 8 OP for their capacity to catalyze isopeptide crosslinking. We treated 100 µg of MAP-rich tubulin with 100 µM chlorpyrifos, chlorpyrifos oxon, methamidophos, paraoxon, diazinon, diazoxon, monocrotophos, or dichlorvos. Each sample was separated on SDS PAGE and stained with Coomassie blue. Five gel slices (at about 30, 50, 150, and 300 kDa, and the top of the separating gel) were removed from the lanes for each of the eight OP samples and from untreated control lanes. These gel slices were subjected to in-gel trypsin digestion. MSMS fragmentation spectra of the tryptic peptides were examined for isopeptide crosslinks. Sixteen spectra yielded convincing evidence for isopeptide crosslinked peptides. Ten were from the chlorpyrifos oxon reaction, 1 from dichlorvos, 1 from paraoxon, 1 from diazinon, and 3 from diazoxon. It was concluded that catalysis of protein crosslinking is a general property of organophosphorus pesticides and pesticide metabolites.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Sus Scrofa Domesticus (domestic Pig)

SUBMITTER: Lawrence Schopfer

LAB HEAD: Oksana Lockridge

PROVIDER: PXD034529 | Pride | 2022-10-14

REPOSITORIES: Pride

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Organophosphorus Pesticides Promote Protein Cross-Linking.

Schopfer Lawrence M LM Onder Seda S Lockridge Oksana O

Chemical research in toxicology 20220901 9

Exposure to organophosphorus pesticides (OP) can have chronic adverse effects that are independent of inhibition of acetylcholinesterase, the classic target for acute OP toxicity. In pure proteins, the organophosphorus pesticide chlorpyrifos oxon induces a cross-link between lysine and glutamate (or aspartate) with loss of water. Tubulin is particularly sensitive to OP-induced cross-linking. Our goal was to explore OP-induced cross-linking in a complex protein sample, MAP-rich tubulin from <i>Su ...[more]

PMID: 36048166

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Project description:Isopeptide crosslinked proteins can be the product of transglutaminase or of exposure to organophosphorus toxicants (OP). Transglutaminase links glutamine to lysine with loss of ammonia. OP toxicants induce a link between glutamic acid and lysine with loss of water. Our goal was to establish criteria to distinguish real from false isopeptide crosslinks reported by software searches of mass spectrometry data. We used fragmentation spectra of tryptic peptides from MAP-rich tubulin Sus scrofa as a test system for detection of naturally-occurring isopeptide crosslinks. Data were analyzed with Protein Prospector. Criteria for the assignments included the presence of at least 1 crosslink specific product ion, fragment ions from both peptides, Protein Prospector scores ≥20, and best fit of the MS/MS data to the crosslinked peptide as opposed to a linear peptide. Out of 301,364 spectra, 15 potential transglutaminase-type crosslinked peptide candidates were identified. Manual evaluation of these MS/MS spectra reduced the number to 1 valid crosslink between Q112 of NFH and K368 of Tau. Immunopurification with anti-isopeptide 81D1C2 confirmed that MAP-rich tubulin contained only one isopeptide. Support for this isopeptide bond was obtained by showing that transglutaminase was capable of incorporating dansyl-aminohexyl -QQIV into K368. A model of the KIETHK-QLEAHNR isopeptide was synthesized with the aid of transglutaminase. MS/MS spectra of the model validated our interpretation of the native isopeptide. An OP-induced isopeptide bond between K163 of tubulin alpha-1A and E158 of tubulin beta-4B was induced by treating MAP-rich tubulin with 100 µM chlorpyrifos oxon. This crosslink was supported by the criteria described above and by the presence of diethoxyphospho-lysine 163 in the tubulin alpha-1A peptide. The information obtained in this work is valuable for future studies that aim to understand why exposure to OP is associated with increased risk of neurodegenerative disease.

Project description:Chlorpyrifos oxon (CPO), the toxic metabolite of the organophosphorus (OP) insecticide chlorpyrifos, causes developmental neurotoxicity in humans and rodents. CPO is hydrolyzed by paraoxonase-1 (PON1), with protection determined by PON1 levels and the human Q192R polymorphism. To examine how the Q192R polymorphism influences fetal toxicity associated with gestational CPO exposure, we measured biomarker inhibition and fetal-brain gene expression in wild-type (PON1+/+), PON1-knockout (PON1-/-), and tgHuPON1R192 and tgHuPON1Q192 transgenic mice. Pregnant mice exposed dermally to 0, 0.50, 0.75 or 0.85 mg/kg/d CPO from gestational days (GD) 6 through 17 were sacrificed on GD18. Biomarkers of CPO exposure inhibited in maternal tissues included brain acetylcholinesterase (AChE), RBC acylpeptide hydrolase (APH), plasma butyrylcholinesterase (BChE) and carboxylesterase (CES). Fetal plasma BChE was inhibited in PON1-/- and tgHuPON1Q192, but not PON1+/+ or tgHuPON1R192 mice. Fetal brain AChE and plasma CES were inhibited in PON1-/- mice, but not in other genotypes. Pregnant mice (wild type (WT), PON1-knockout (KO), tgHuPON1R192 (R-tg) and tgHuPON1Q192 (Q-tg)) were exposed to various amounts of CPO (0, 0.5, 0.75 and 0.85 mg/kg/d) for 12 days (gestational days 6-17). On gestational day 18, dams were sacrificed and fetal brains were collected. A total of 264 fetal brains from 80 dams were processed to extract total RNA using TRIZOL and the QIAamp Tissue kit from QIAGEN. Microarray analysis was performed using the fetuses of 5 dams per experimental group (total RNA was pooled from individual fetal brains from each dam). The dams used for fetal-brain microarray analysis were selected using a random-number generator, after first eliminating dams with brain AChE activities > 1.5 SD compared to the mean for their treatment group. RNA samples isolated from individual fetal brains from each dam were combined, then labeled and hybridized to Affymetrix Mouse Gene 1.0 ST microarrays.

Dataset Information

Organophosphorus pesticides catalyze protein crosslinking

Publications

Organophosphorus Pesticides Promote Protein Cross-Linking.

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