Maxillary palp odorant-binding proteins as key mediators of bitter taste and molecular targets for cockroach control

The German cockroach (Blattella germanica) is a notorious urban pest with significant health impacts, owing in part to its highly sophisticated gustatory system that enables precise food discrimination and toxin avoidance. Odorant-binding proteins (OBPs) are known to play critical roles in insect chemoreception, yet their specific contributions to sweet and bitter compound recognition remain poorly understood.

We investigated the function of three maxillary palp-enriched OBPs (BgerOBP10, BgerOBP44, and BgerOBP91) using fluorescence competitive binding assays, RNA interference (RNAi), bitter selection behavioral assays, analytical ultracentrifugation, and structural modeling with AlphaFold-3 followed by molecular docking.

Binding assays identified Berberine chloride hydrate and Vanillin as potential bitter ligands of the three OBPs. RNAi efficiently suppressed their expression in both male and female maxillary palps, leading to loss of bitter discrimination: while control cockroaches avoided bitter sources, OBP-deficient individuals failed to distinguish them from water. Analytical ultracentrifugation revealed that recombinant BgerOBP91 forms dimers, and structural predictions showed distinct 3D conformations and unique ligand-interacting residues among the three OBPs. Taken together, the present study demonstrates, for the first time, that maxillary palp OBPs mediate bitter perception in B. germanica. By uncovering novel molecular mechanisms of gustation, our findings not only expand the functional repertoire of insect OBPs but also provide promising molecular targets for the development of innovative strategies to disrupt cockroach feeding behavior and pest management.