Functional characterization of AsOBP21f, an odorant-binding protein involved in human odor detection in the malaria vector Anopheles sinensis

Abstract Background Olfactory detection of host odors is fundamental to mosquito host-seeking behavior. Although the olfactory pathways of model species such as Anopheles gambiae have been well characterized, the molecular basis of human odor detection in Anopheles sinensis, an important malaria vector in Asia with opportunistic feeding habits, remains poorly understood. This study systematically investigates the functional role of the odorant-binding protein AsOBP21f in this process. Methods AsOBP21f was cloned and characterized using bioinformatics, quantitative reverse transcription PCR (RT-qPCR), and phylogenetic analyses. Recombinant AsOBP21f protein was expressed and purified for fluorescence competitive binding assays with 35 human odorants. Molecular docking was performed to elucidate ligand-binding interactions. Electroantennogram (EAG) recordings and behavioral assays were conducted to evaluate mosquito responses to high-affinity ligands. RNA interference (RNAi) knockdown was used to assess the functional role of AsOBP21f in host-seeking and blood-feeding behavior. Results AsOBP21f was predominantly expressed in olfactory tissues of mosquito females, including the antennae and proboscis. Its protein exhibited notable selectivity for hydrophobic odor molecules with C10–C15 carbon chains, and had strong binding affinities for methyl tridecanoate, dodecanal, decanal, and pentadecanoic acid. Behavioral experiments further demonstrated dose-dependent effects of these ligands; methyl tridecanoate showed significant attraction, while dodecanal exhibited clear repellency. RNAi-mediated silencing of AsOBP21f significantly reduced the antennal electrophysiological response of mosquito females to host odors and markedly decreased blood-feeding success. Conclusions These results highlight the role of AsOBP21f in host-seeking behavior through the detection of human odors, such as methyl tridecanoate, in An. sinensis, providing a potential target for malaria control. Graphical Abstract