p.Met303Ile n.G909A. For S250T W251S M303I L334L W378R S383T majority of female carried the homozygous susceptible allele in susceptible strain while males were primary heterozygous for these alleles. In resistant strains both male and females were homozygous for the mutation. T found also in some suceptible strains Zhang et al. 2010 Claudianos et al. 1999 and M found in Rutgers resistant strain
Kinetic parameters
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References:
Title: Multiple mutations and overexpression of the MdaE7 carboxylesterase gene associated with male-linked malathion resistance in housefly, Musca domestica (Diptera: Muscidae) Zhang Y, Li J, Ma Z, Shan C, Gao X Ref: Sci Rep, 8:224, 2018 : PubMed
Two unique housefly strains, MSS and N-MRS, were selected and used to clarify mechanisms of sex-associated malathion resistance in the housefly, Musca domestica. Compared with the lab-susceptible CSS strain, susceptible females and resistant males were observed in the malathion-susceptible MSS strain, while the malathion-resistant near-isogenic line, N-MRS, achieved similar resistance level between genders. Significant synergistic effect of the esterase-inhibitor DEF on resistant houseflies pointed to the important involvement of esterase in this specific malathion resistance. Examination of the carboxylesterase gene MdalphaE7 in malathion resistant housefly populations found seven, non-synonymous SNP mutations (Ser(250)-Thr, Trp(251)-Ser, Met(303)-Ile, Leu(354)-Phe, Ser(357)-Leu, Trp(378)-Arg and Ser(383)-Thr), not found in susceptible houseflies, revealing a strong correlation between these mutations and the development of malathion resistance. Further genetic analysis conducted with bioassays by topical application and nucleotide polymorphism detection provided a first line of molecular evidence for a linkage between a male-determining factor and MdalphaE7 gene in the MSS and N-MRS males. This linkage results in a much higher level of malathion resistance for males than females in the MSS strain. Lastly, quantitative real-time PCR showed that MdalphaE7 was over expressed in the resistant strain due to the increased transcription level of mRNA rather than gene duplication.
Title: Quantitative and qualitative changes of the carboxylesterase associated with beta-cypermethrin resistance in the housefly, Musca domestica (Diptera: Muscidae) Zhang L, Shi J, Shi X, Liang P, Gao J, Gao X Ref: Comparative Biochemistry & Physiology B Biochem Mol Biol, 156:6, 2010 : PubMed
Mechanisms of esterase-mediated pyrethroid resistance were analyzed based on our previous works in a strain of the housefly, Musca domestica. The carboxylesterase gene, MdalphaE7, was cloned and sequenced from susceptible (CSS) and resistant (CRR) strains, and a total of nine amino acid substitutions were found. The mutation, Trp(251)-Ser appeared to play a role in beta-cypermethrin resistance and cross-resistance between organophosphates (OPs) and pyrethroids in the CRR strain. Quantitative real-time PCR showed that MdalphaE7 was over-expressed in the CRR strain, the reciprocal cross progeny F(1) and back-cross progeny BC(2) compared with the CSS strain, respectively. Two alpha-cynaoester substrates as surrogates for beta-cypermethrin and deltamethrin, were synthesized to determine the pyrethroid hydrolase activity. Results showed that carboxylesterases from the CRR strain hydrolyzed cypermethrin/deltamethrin-like substrate 9.05- and 13.53-fold more efficiently than those from the CSS strain, respectively. Our studies suggested that quantitative and qualitative changes in the carboxylesterase might contribute together to pyrethroid resistance in the CRR strain.
