Identification of a novel class of insect glutathione S-transferases involved in resistance to DDT in the malaria vector Anopheles gambiae

The sequence and cytological location of five Anopheles gambiae glutathione S-transferase (GST) genes are described. Three of these genes, aggst1-8, a ggst1-9 and aggst1-10, belong to the insect class I family and are located on chromosome 2R, in close proximity to previously described members of thi s gene family. The remaining two genes, aggst3-1 and aggst3-2, have a low s equence similarity to either of the two previously recognized classes of in sect GSTs and this prompted a re-evaluation of the classification of insect GST enzymes. We provide evidence for seven possible classes of insect prot ein with GST-like subunits. Four of these contain sequences with significan t similarities to mammalian GSTs. The largest novel insect GST class, class III, contains functional GST enzymes including two of the A. gambiae GSTs described in this report and GSTs from Drosophila melanogaster, Musca domes tica, Manduca sexta and Plutella xylostella. The genes encoding the class I II GST of A. gambiae map to a region of the genome on chromosome 3R that co ntains a major DDT [1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane] resista nce gene, suggesting that this gene family is involved in GST-based resista nce in this important malaria vector. In further support of their role in r esistance, we show that the mRNA levels of aggst3-2 are approx. 5-fold high er in a DDT resistant strain than in the susceptible strain and demonstrate that recombinant AgGST3-2 has very high DDT dehydrochlorinase activity.