Juvenile hormone (JH) is a key lipophilic hormone that regulates metamorphosis, behavior, reproduction, and other key biological events in all insects. JH is a sesquiterpenoid with a methyl ester moity at one end and epoxide moity at the other (Figure below). Our laboratory has advanced the hypothesis that JH titer is regulated not only by its biosynthesis, but also by its metabolism and possibly sequestration. JH is primarily metabolized by two hydrolytic enzymes in the ?/?-hydrolase fold family known as JH esterase (JHE) and JH epoxide hydrolase (JHEH). JHE and JHEH may also function as synthetic enzymes in terms of the production of JH acid, JH diol, and/or JH acid-diol (Figure below).
We have recently determined the 2.7 Å crystal structure of JHE of the tobacco hornworm Manduca sexta (Figure below).
We are currently using this structural information to gain mechanistic insights into the catalytic activity, degradation, and inhibition of JHE. Highly potent transition state esterase inhibitors such as OTFP (3-octylthio-1,1,1-trifluoropropan-2-one) have been synthesized in our laboratory that allow us to specifically study the biological efficacy of JHE. This has been most clearly shown in lepidopterous larvae where inhibition of JHE reduces the rate of JH degradation and leads to massive larvae and delayed pupation (Figure below). We are currently attempting to design similarly active inhibitors against JHEH. The availability of these and other tools will allow us to test the relative and combined importance of JHE and JHEH in insect development.
Insect Development Biology
Another emphasis of this laboratory is the identification and characterization of insecticide detoxification enzymes and insecticide target proteins, and their genes. Our goal is to use our understanding of insecticide resistance mechanisms to prevent or reduce the incidence of insecticide resistance. One current focus is on the role that esterase(s) and glutathione S-transferase(s) (GST) play in the dextoxification of pyrethroid insecticides such as permethrin (Figure left) in mosquito.
We believe that synthetic chemical and biological insecticides will be an integral part of the management of pest insect populations in agriculture and public health for the foreseeable future. The development of insecticide resistance due to overuse, misuse, and/or natural selection, however, is limiting our ability effectively control some insect populations.
Another focus is understanding how mosquitoes become resistant to methoprene. Methoprene is a “green” insecticide that mimics the structure and function of JH (Figure right).
Another goal of this laboratory is the development of quantitative and high throughput assays for the rapid detection of insecticide resistance. In this regard, we have developed a number of pyrethroid-like fluorescent substrates (Figure below) that we hope will be useful in field-applicable detection of pyrethroid resistance.