Biochemical analysis of a blood meal-induced Aedes aegypti glutamine synthetase gene

Glutamine synthetase (GS) in the mosquito, Aedes aegypti, is induced in the midgut following a blood meal. Mosquito GS message is detected as soon as 1 h post-blood feeding and remains stable for 18 h. Using a PCR product encoding mosquito GS, a lambda gt10 adult female mosquito cDNA library was screened. A cDNA clone, pCl5A2, encoding the full translation product of mosquito GS was isolated and sequence analyses performed. Mosquito GS cDNA is 2.5 kb in length and its putative translation product shares all the conserved regions characteristic of the GS gene family, including the presumed ATP biding site. Glutamine synthetase activity in the mosquito midgut is highest at 18 h post-blood feeding. Activity can be detected over a broad pH range, from 6.0 to 7.5. Unlike other cellular GS enzymes, mosquito GS is not active in the presence of ATP. Very low dosages (0.05 mM) of L-methionine S-sulfoximine are sufficient to partially inhibit mosquito GS activity. Inhibition of GS disrupts the normal formation of the midgut peritrophic matrix, suggesting that GS enzyme might be involved in the initial pathway of chitin synthesis. The unique expression pattern and inducible nature of the mosquito GS gene make it an interesting candidate for studying promoter function. Additionally, the blood meal activation of the GS gene makes this a potentially valuable tool in mosquito transformation studies.