Loss of the membrane anchor of the target receptor is a mechanism of bioinsecticide resistance.
The mosquitocidal activity of Bacillus sphaericus is because of a binary toxin (Bin), which binds to Culex pipiens maltase 1 (Cpm1), an alpha-glucosidase present in the midgut of Culex pipiens larvae. In this work, we studied the molecular basis of the resistance to Bin developed by a strain (GEO) of C. pipiens. Immunohistochemical and in situ hybridization experiments showed that Cpm1 was undetectable in the midgut of GEO larvae, although the gene was correctly transcribed. The sequence of the cpm1(GEO) cDNA differs from the sequence we previously reported for a susceptible strain (cpm1(IP)) by seven mutations: six missense mutations and a mutation leading to the premature termination of translation. When produced in insect cells, Cpm1(IP) was attached to the membrane by a glycosylphosphatidylinositol (GPI). In contrast, the premature termination of translation of Cpm1(GEO) resulted in the targeting of the protein to the extracellular compartment because of truncation of the GPI-anchoring site. The interaction between Bin and Cpm1(GEO) and the enzyme activity of the receptor were not affected. Thus, Bin is not toxic to GEO larvae because it cannot interact with the midgut cell membrane, even though its receptor site is unaffected. This mechanism contrasts with other known resistance mechanisms in which point mutations decrease the affinity of binding between the receptor and the toxin.
Darboux
Isabelle
I
Institut National de la Recherche Agronomique, Unité Mixte de Recherche 1112 "Réponses des Organismes aux Stress Environnementaux," 123 Boulevard Meilland, B.P. 2078, 06606 Antibes Cedex, France.
Pauchet
Yannick
Y
Castella
Claude
C
Silva-Filha
Maria Helena
MH
Nielsen-LeRoux
Christina
C
Charles
Jean-François
JF
Pauron
David
D
D000818:Animals; D001427:Bacterial Toxins / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D003465:Culex / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D017261:Glycosylphosphatidylinositols / Q000378:metabolism; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007313:Insecta; D007305:Insecticide Resistance / Q000502:physiology*; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism; D009154:Mutation; D020125:Mutation, Missense; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D010957:Plasmids / Q000378:metabolism; D017354:Point Mutation; D011485:Protein Binding; D014176:Protein Biosynthesis; D011956:Receptors, Cell Surface / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection; D010738:Type C Phospholipases / Q000378:metabolism; D000520:alpha-Glucosidases / Q000378:metabolism
C405322:Bacillus sphaericus binary toxin receptor; D001427:Bacterial Toxins; D018076:DNA, Complementary; D017261:Glycosylphosphatidylinositols; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; C046134:binB protein, Bacillus sphaericus; D010738:Type C Phospholipases; D000520:alpha-Glucosidases; D043265:Phosphatidylinositol Diacylglycerol-Lyase