Submitted to: Journal of Insect Biochemistry and Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/1999
Publication Date: N/A
Interpretive Summary: Although the cattle fever tick (CFT) and the disease it transmits, babesiosis, were eradicated from the US after a 50-year eradication program of dipping cattle and temporarily vacating tick-infested pastures, they are still widespread in Mexico and other parts of America. Quarantine by vat dipping with chemical pesticides has prevented reinfestation in the US. But the CFT has developed resistance to such pesticides which means it takes more and more of the pesticides to kill the ticks. An understanding of the mechanisms of pesticide resistance can help develop better pest management strategies and prolong the usefulness of the currently available pesticides. One common mechanism of resistance to pesticides in insects and ticks is the altered activity of enzymes that destroy the pesticides. The precise manner of how the enzyme activity is altered can only be understood if the information is available on biochemical and molecular properties of the enzyme. Glutathione S-transferase is one of the detoxifying enzymes implicated in pesticide resistance in insects. We purified this enzyme and compared the genetic blueprints of this enzyme between pesticide-resistant and susceptible strains of ticks. No changes were found in the resistant strain. The resistance could still result from an increased level of this enzyme, a possibility currently under investigation. The sequencing of the glutathione S-transferase gene will help us understand the mechanism(s) of pesticide resistance in the CFT.
Technical Abstract: A glutathione S-transferase (GST) was purified from the larval cattle ticks Boophilus microplus (Acari:Ixodidae), by glutathione-affinity chromatography. The purified enzyme appeared as a single band on SDS-PAGE and has a molecular mass of 25.8 kDa determined by mass spectrometry. The N-terminus of the purified enzyme was sequenced. The full-length cDNA of the enzyme was isolated by RT-PCR using degenerate oligonucleotides derive from the N-terminal amino acid sequence. The cDNA contains an open reading frame encoding a 223-amino-acid protein with the N-terminus identical to the purified GST. Comparison of the deduced amino acid sequence with GSTs from other species revealed that the enzyme is closely related to the mammalian mu class GST.