Binding of Aedes aegypti trypsin modulating oostatic factor [Aea-TMOF] to its receptor stimulates phosphorylation and protease processing of gut-membrane proteins

The binding of TMOF to its gut receptor was followed by incubating guts removed from male and female Aedes aegypti. TMOF at physiological concentrations, in the presence of [γ32P]ATP, causes phosphorylation and release of gut-membrane protein (45 kDa) that is further processed by proteolysis. In the presence of protease inhibitors only the 45 kDa protein was released. The phosphorylation and processing of the 45 kDa protein does not happen in the absence of TMOF. Both larvae and adult guts release the protein in the presence of TMOF. Male Ae. aegypti do not synthesize trypsin in their gut and do not release the 45 kDa protein in the presence of TMOF because a TMOF receptor is probably absent. Homogenized guts do not release the 45 kDa protein, indicating that the protease processing or the ecto-protein kinase activity is probably reduced after breaking the tissue. The 45 kDa phosphorylated protein can be dephosphorylated by alkaline phosphatase and protein phosphatase, indicating that the phosphate group is covalently linked to either a serine or a tyrosine moiety. This is the first report that shows that in insects, binding of a peptide hormone activates its receptor by proteolysis.