Gene_locus Report for: aphgo-ACHE2

Two acetylcholinesterase genes, Ace1 and Ace2, have been fully cloned and sequenced from both organophosphate-resistant and susceptible clones of cotton aphid. Comparison of both nucleic acid and deduced amino acid sequences revealed considerable nucleotide polymorphisms. Further study found that two mutations occurred consistently in all resistant aphids. The mutation F139L in Ace2 corresponding to F115S in Drosophila acetylcholinesterase might reduce the enzyme sensitivity and result in insecticide resistance. The other mutation A302S in Ace1 abutting the conserved catalytic triad might affect the activity and insecticide sensitivity of the enzyme. Phylogenetic analysis showed that insect acetylcholinesterases fall into two subgroups, of which Ace1 is the paralogous gene whereas Ace2 is the orthologous gene of Drosophila AChE. Both subgroups contain resistance-associated AChE genes. To avoid confusion in the future work, a nomenclature of insect AChE is also suggested in the paper.

Gene sequences encoding putative acetylcholinesterases have been reported for four hemipteran insect species. Although acetylcholinesterase insensitivity occurs in insecticide-resistant populations of each of these species, no mutations were detected in the gene sequences from the resistant insects. This, coupled with a series of experiments using novel reversible inhibitors to compare the biochemical characteristics of acetylcholinesterase from a range of insect species, showed that the cloned cDNA fragments are unlikely to encode the hemipteran synaptic acetylcholinesterases, and there is likely to be a second ace locus.

Two acetylcholinesterase (AChE) genes, Ace1 and Ace2, have been cloned from cotton aphid, Aphis gossypii Glover, using the rapid amplification of cDNA ends (RACE) technique. To the best of our knowledge, this should be the first direct molecular evidence that multiple AChE genes exist in insects. The Ace1 gene was successfully amplified along its full length of 2371 bp. The open reading frame is 2031 bp long and encodes 676 amino acids (GenBank accession No. AF502082). The Ace2 gene was amplified as a mega-fragment of 2130 bp lacking part of 5'-end untranslated region (UTR). The open reading frame is 1992 bp long and ecodes a protein of 664 amino acids (GenBank accession No. AF502081). Both genes have the conserved amino acids and features shared by the AChE family, but share only 35% identity in amino acid sequence. The Ace1 gene is highly homologous to the AChE gene of Schizaphis graminum (AF321574) with 95% identity, and Ace2 to that of Myzus persicae (AF287291) with 92% identity. Phylogenetic analysis showed that the two cloned AChEs of A. gossypii are different in evolution. The phylogenetic tree generated by the PHYLIP program package inferred that AChE2 of A. gossypii is a more ancestral form of AChE. Homology modeling of structures using Torpedo californica (2ACE_) and Drosophila melanogaster (1Q09:A) native acetylcholinesterase structure as main template indicated that the two AChEs of Aphis gossypii might have different three-dimensional structures. Alternative splicing of Ace1 near the 5'-end resulting in two proteins differing by the presence or absence of a fragment of four amino acids is also reported.

Two acetylcholinesterase genes, Ace1 and Ace2, have been fully cloned and sequenced from both organophosphate-resistant and susceptible clones of cotton aphid. Comparison of both nucleic acid and deduced amino acid sequences revealed considerable nucleotide polymorphisms. Further study found that two mutations occurred consistently in all resistant aphids. The mutation F139L in Ace2 corresponding to F115S in Drosophila acetylcholinesterase might reduce the enzyme sensitivity and result in insecticide resistance. The other mutation A302S in Ace1 abutting the conserved catalytic triad might affect the activity and insecticide sensitivity of the enzyme. Phylogenetic analysis showed that insect acetylcholinesterases fall into two subgroups, of which Ace1 is the paralogous gene whereas Ace2 is the orthologous gene of Drosophila AChE. Both subgroups contain resistance-associated AChE genes. To avoid confusion in the future work, a nomenclature of insect AChE is also suggested in the paper.

The complete coding sequences of two acetylcholinesterase (AChE) genes, Ace1 (orthologous to Drosophila Ace) and Ace2 (paralogous to Ace), from the cotton aphid (Aphis gossypii) were identified and sequences from carbamate resistant and susceptible strains compared. No change in the amino acid sequences was found in Ace1, while two amino acid substitutions, Ser431Phe and Ala302Ser, were detected between resistant and susceptible strains in Ace2. The position of Ser431Phe corresponds to one of fourteen aromatic residues lining the active site gorge and is located in the acyl pocket. Ala302Ser is located at one of the three residues which form the oxyanion hole in the active site of AChE. The Ser431Phe and Ala302Ser substitutions may play a role in pirimicarb and organophosphate resistance, respectively.

Gene sequences encoding putative acetylcholinesterases have been reported for four hemipteran insect species. Although acetylcholinesterase insensitivity occurs in insecticide-resistant populations of each of these species, no mutations were detected in the gene sequences from the resistant insects. This, coupled with a series of experiments using novel reversible inhibitors to compare the biochemical characteristics of acetylcholinesterase from a range of insect species, showed that the cloned cDNA fragments are unlikely to encode the hemipteran synaptic acetylcholinesterases, and there is likely to be a second ace locus.

Two acetylcholinesterase (AChE) genes, Ace1 and Ace2, have been cloned from cotton aphid, Aphis gossypii Glover, using the rapid amplification of cDNA ends (RACE) technique. To the best of our knowledge, this should be the first direct molecular evidence that multiple AChE genes exist in insects. The Ace1 gene was successfully amplified along its full length of 2371 bp. The open reading frame is 2031 bp long and encodes 676 amino acids (GenBank accession No. AF502082). The Ace2 gene was amplified as a mega-fragment of 2130 bp lacking part of 5'-end untranslated region (UTR). The open reading frame is 1992 bp long and ecodes a protein of 664 amino acids (GenBank accession No. AF502081). Both genes have the conserved amino acids and features shared by the AChE family, but share only 35% identity in amino acid sequence. The Ace1 gene is highly homologous to the AChE gene of Schizaphis graminum (AF321574) with 95% identity, and Ace2 to that of Myzus persicae (AF287291) with 92% identity. Phylogenetic analysis showed that the two cloned AChEs of A. gossypii are different in evolution. The phylogenetic tree generated by the PHYLIP program package inferred that AChE2 of A. gossypii is a more ancestral form of AChE. Homology modeling of structures using Torpedo californica (2ACE_) and Drosophila melanogaster (1Q09:A) native acetylcholinesterase structure as main template indicated that the two AChEs of Aphis gossypii might have different three-dimensional structures. Alternative splicing of Ace1 near the 5'-end resulting in two proteins differing by the presence or absence of a fragment of four amino acids is also reported.