Chlorpyrifos oxon promotes tubulin aggregation via isopeptide cross-linking between diethoxyphospho-Lys and Glu or Asp: Implications for neurotoxicity.

ABSTRACT: Exposure to organophosphorus toxicants (OP) can have chronic adverse effects that are not explained by inhibition of acetylcholinesterase, the cause of acute OP toxicity. We therefore hypothesized that OP-induced chronic illness is initiated by the formation of organophosphorus adducts on lysine residues in proteins, followed by protein cross-linking and aggregation. Here, Western blots revealed that exposure to the OP chlorpyrifos oxon converted porcine tubulin from its original 55-kDa mass to high-molecular-weight aggregates. Liquid chromatography-tandem MS analysis of trypsin-digested samples identified several diethoxyphospho-lysine residues in the OP-treated tubulin. Using a search approach based on the Batch Tag program, we identified cross-linked peptides and found that these chemically activated lysines reacted with acidic amino acid residues creating ?-glutamyl-?-lysine or aspartyl-?-lysine isopeptide bonds between ?- and ?-tubulin. Of note, these cross-linked tubulin molecules accounted for the high-molecular-weight aggregates. To the best of our knowledge, this is the first report indicating that chlorpyrifos oxon-exposed tubulin protein forms intermolecular cross-links with other tubulin molecules, resulting in high-molecular-weight protein aggregates. It is tempting to speculate that chronic illness from OP exposure may be explained by a mechanism that starts with OP adduct formation on protein lysines followed by protein cross-linking. We further speculate that OP-modified or cross-linked tubulin can impair axonal transport, reduce neuron connections, and result in neurotoxicity.

SUBMITTER: Schopfer LM 

PROVIDER: S-EPMC6120212 | biostudies-literature | 2018 Aug

REPOSITORIES: biostudies-literature