Odorant-binding proteins and chemosensory proteins in insects: structural insights, functional plasticity, and...

Odorant-binding proteins (OBPs) and chemosensory proteins (CSPs) are integral to the chemical communication systems of insects, mediating the detection, transport, and discrimination of hydrophobic ligands such as pheromones, odorants, and xenobiotics. While OBPs are largely confined to olfactory tissues and exhibit high structural specificity-with six conserved cysteines forming three disulfide bridges-CSPs are structurally simpler, featuring four conserved cysteines and two disulfide bridges, yet display remarkable conformational plasticity and functional versatility. Recent evidence underscores the roles of CSPs beyond chemoreception, including developmental regulation, cuticle formation, visual pigment transport, nutrient solubilization, reproductive signaling, and notably, insecticide resistance-where upregulation in response to chemical stress suggests a role in sequestration and detoxification. CSPs are expressed ubiquitously across diverse tissues, including reproductive and digestive organs, and have been identified in seminal fluids, where they may facilitate pheromone delivery or mating plug formation. Comparative genomic analyses reveal significant interspecific variability in OBP and CSP gene families, with expansions in certain taxa corresponding to ecological and behavioral adaptations. Emerging transcriptomic and gene-editing studies (e.g., RNAi, CRISPR) are elucidating their tissue-specific expression and ligand-binding properties, opening new avenues for functional annotation and pest control applications. This review synthesizes current advances in the structure, evolution, and multifunctionality of OBPs and CSPs, highlighting their roles as molecular chaperones in insect physiology. Understanding these proteins provides crucial insights into insect chemical ecology and offers promising molecular targets for sustainable pest management strategies through behavioral disruption or chemosensory interference.