Reflections on antennal proteins: The evolution of pheromone binding proteins; diversity of pheromone degrading enzymes; and the distribution and behavioral roles of SNMPs

Pheromone and other odor molecules are detected by chemosensory neurons housed within olfactory and taste/contact sensilla. Proteins involved in this detection process include Odor Receptors, Odorant Binding Proteins, Odor Degrading Enzymes and membrane proteins called SNMPs. In this chapter we discuss the origins, evolution and uniqueness of the Lepidoptera specific OBPs Pheromone Binding Proteins (PBPs) and General Odorant Binding Proteins (GOBPs) whose genes are largely organized into a single gene cluster. We then comment on the diversity of Odor and Pheromone Degrading Enzymes and enzymatic activities, their roles in signal termination, and their potential as targets in insect control. Finally, we present studies examining the spatial-and co-expression of SNMP1 and SNMP2 in Drosophila, and the behavioral effects of deleting their genes: SNMP1 and SNMP2 frequently co-express in the same sensilla, both olfactory and taste, but often differentially with one expressing in neurons and the other in support cells; SNMP1 gene knockouts affect fitness and both male-female and male-male courtship, while SNMP2 knockouts affect fitness and male-male courtship but not male-female courtship. We encourage consideration of additional roles for all these proteins, and for evaluating these proteins in an ethological context.