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Article

Chlorpyrifos Oxon-Induced Isopeptide Bond Formation in Human Butyrylcholinesterase

1
Department of Biochemistry, School of Pharmacy, Hacettepe University, Ankara 06230, Turkey
2
Eppley Institute, University of Nebraska Medical Center, Omaha, NE 68198-5900, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Zrinka Kovarik
Molecules 2020, 25(3), 533; https://doi.org/10.3390/molecules25030533
Received: 3 January 2020 / Revised: 21 January 2020 / Accepted: 22 January 2020 / Published: 25 January 2020
(This article belongs to the Special Issue Enzymes Reacting with Organophosphorus Compounds)
A newly recognized action of organophosphates (OP) is the ability to crosslink proteins through an isopeptide bond. The first step in the mechanism is covalent addition of the OP to the side chain of lysine. This activates OP-lysine for reaction with a nearby glutamic or aspartic acid to make a gamma glutamyl epsilon lysine bond. Crosslinked proteins are high molecular weight aggregates. Our goal was to identify the residues in the human butyrylcholinesterase (HuBChE) tetramer that were crosslinked following treatment with 1.5 mM chlorpyrifos oxon. High molecular weight bands were visualized on an SDS gel. Proteins in the gel bands were digested with trypsin, separated by liquid chromatography and analyzed in an Orbitrap mass spectrometer. MSMS files were searched for crosslinked peptides using the Batch-Tag program in Protein Prospector. MSMS spectra were manually evaluated for the presence of ions that supported the crosslinks. The crosslink between Lys544 in VLEMTGNIDEAEWEWK544AGFHR and Glu542 in VLEMTGNIDEAEWE542WK satisfied our criteria including that of spatial proximity. Distances between Lys544 and Glu542 were 7.4 and 9.5 Å, calculated from the cryo-EM (electron microscopy) structure of the HuBChE tetramer. Paraoxon ethyl, diazoxon, and dichlorvos had less pronounced effects as visualized on SDS gels. Our proof-of-principle study provides evidence that OP have the ability to crosslink proteins. If OP-induced protein crosslinking occurs in the brain, OP exposure could be responsible for some cases of neurodegenerative disease. View Full-Text
Keywords: mass spectrometry; isopeptide; chlorpyrifos oxon; crosslinked peptides; butyrylcholinesterase mass spectrometry; isopeptide; chlorpyrifos oxon; crosslinked peptides; butyrylcholinesterase
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MDPI and ACS Style

Biberoglu, K.; Tacal, O.; Schopfer, L.M.; Lockridge, O. Chlorpyrifos Oxon-Induced Isopeptide Bond Formation in Human Butyrylcholinesterase. Molecules 2020, 25, 533. https://doi.org/10.3390/molecules25030533

AMA Style

Biberoglu K, Tacal O, Schopfer LM, Lockridge O. Chlorpyrifos Oxon-Induced Isopeptide Bond Formation in Human Butyrylcholinesterase. Molecules. 2020; 25(3):533. https://doi.org/10.3390/molecules25030533

Chicago/Turabian Style

Biberoglu, Kevser; Tacal, Ozden; Schopfer, Lawrence M.; Lockridge, Oksana. 2020. "Chlorpyrifos Oxon-Induced Isopeptide Bond Formation in Human Butyrylcholinesterase" Molecules 25, no. 3: 533. https://doi.org/10.3390/molecules25030533

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