SNMPs Function as Molecular Bridges between OBPs and ORs in the Olfactory Recognition of Clostera Retitura (Walker) (Lepidoptera: Notodontidae).

Odorant-binding proteins (OBPs) and odorant receptors (ORs) are regarded as key proteins in the moth olfactory system. Sensory neuron membrane proteins (SNMPs) are also thought to play important roles, although the underlying mechanism remains elusive. Three SNMP genes, two candidate PBP genes, and three candidate PR genes were identified from Clostera restitura. Phylogenetic analysis showed that CresSNMP1 × 1 and CresSNMP1 × 2 were paralogs belonging to the lepidopteran SNMP1 subfamily, whereas SNMP2 consistently clustered within the SNMP2 clade. Only CresSNMP1 × 1 exhibited male-biased expression in adults, whereas SNMP2 presented an extremely high expression level in adult antennae and a stable expression profile from 1st to 5th instar larvae. These findings align with the well-established role of SNMP1 in pheromone detection, whereas SNMP2 may have both olfactory and nonolfactory functions. Multi-protein docking and split-ubiquitin yeast two-hybrid assays indicated that CresSNMPs, especially SNMP1, interact with both OBPs and candidate ORs, suggesting that SNMPs may function as molecular bridges between OBPs and ORs, facilitating the transfer of odorant molecules from OBPs to a specific OR subunits within the heterotetrameric complex.