Functional and structural characterization of an insect mevalonate pathway enzyme

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Conventional chemical insecticides tend to have detrimental impacts on non-target organisms, including humans. For this reason, there is increasing pressure to limit their use in forestry and agriculture. One of the strategies currently implemented for the discovery of safer alternatives involves the development of molecules that disrupt biochemical processes that are specific to a group of insects, because such molecules are unlikely to have serious negative effects on non-target organisms. Before developing these molecules, however, one must first identify physiological and biochemical processes that are amenable to being fatally disrupted, and develop a thorough knowledge of the underlying mechanisms, including a characterization of the proteins (typically enzymes or receptors) that will be targeted for disruption. The present research focuses on an enzyme (farnesyl diphosphate synthase or FPPS) that plays a critical role in several physiological processes, including the regulation of metamorphosis and reproduction in insects. As such, this enzyme is essential to the synthesis of "juvenile hormone" (JH), a terpenoid compound that controls insect development and egg maturation. JH biosynthesis is an appropriate target for disruption because its inhibition has profound effects on these two processes. In a group of insects known as the Lepidoptera (caterpillars, moths, butterflies), we have isolated two very distinct FPPSs, both exhibiting features that set them apart from other, "conventional" forms of this enzyme. For this reason, the development of inhibitors that are specific to lepidopteran FPPSs (i.e., with no or little effect on the corresponding enzyme in other organisms) appears possible. To design inhibitors with optimal potency towards these enzymes, we need information about the enzymes' three-dimensional structures. Indeed, inhibitors must fit into a cleft within the enzyme, just like a key fits into a lock. In addition, their roles in JH biosynthesis and other physiological processes must be well characterized. The present research addresses these issues through (i) the design of novel FPPS inhibitors, (ii) structural assessments of how they fit within the enzyme's active site, (iii) measurement of their inhibitory potency, and (iv) probing of their different physiological functions. Such inhibitors could form the basis of novel, caterpillar-specific insecticides.