Abstract
The bamboo snout beetle Cyrtotrachelus buqueti is a widely distributed wood-boring pest found in China, and its larvae cause significant economic losses because this beetle targets a wide range of host plants. A potential pest management measure of this beetle involves regulating olfactory chemoreceptors. In the process of olfactory recognition, pheromone-binding proteins (PBPs) play an important role. Homology modeling and molecular docking were conducted in this study for the interaction between CbuqPBP1 and dibutyl phthalate to better understand the relationship between PBP structures and their ligands. Site-directed mutagenesis and binding experiments were combined to identify the binding sites of CbuqPBP1 and to explore its ligand-binding mechanism. The 3D structural model of CbuqPBP1 has six a-helices. Five of these a-helices adopt an antiparallel arrangement to form an internal ligand-binding pocket. When docking dibutyl phthalate within the active site of CbuqPBP1, a CH-π interaction between the benzene ring of dibutyl phthalate and Phe69 was observed, and a weak hydrogen bond formed between the ester carbonyl oxygen and His53. Thus, Phe69 and His53 are predicted to be important residues of CbuqPBP1 involved in ligand recognition. Site-directed mutagenesis and fluorescence assays with a His53Ala CbuqPBP1 mutant showed no affinity toward ligands. Mutation of Phe69 only affected binding of CbuqPBP1 to cedar camphor. Thus, His53 (Between α2 and α3) of CbuqPBP1 appears to be a key binding site residue, and Phe69 (Located at α3) is a very important binding site for particular ligand interactions.
Highlights
During long-term evolution insects have developed a sensitive sense of smell, which enables insects to detect external volatile semiochemicals when searching for various environmental cues, such as foraging for food, finding a breeding partner and locating a spawning ground (Gu et al, 2011; Larsson et al, 2004)
The results provide a platform for using pheromones to prevent and control C. buqueti efficiently
The structural characteristics of CbuqPBP1 are similar to other sex pheromone binding proteins and include six α-helices: residues 26–36 (α1), 44–51 (α2), 59–72 (α3), 83–94 (α4), 101–114 (α5) and 123–137 (α6)
Summary
During long-term evolution insects have developed a sensitive sense of smell, which enables insects to detect external volatile semiochemicals when searching for various environmental cues, such as foraging for food, finding a breeding partner and locating a spawning ground (Gu et al, 2011; Larsson et al, 2004). Receptors are widely distributed with various olfactoryrated functional proteins, including odorant binding proteins (OBPs), chemosensory proteins (CSPs) and olfactory receptors (Ors). Kruse et al (2003) and Thode et al (2008) initially analyzed the general odorant binding protein (LUSH) of Drosophila melanogaster and the crystal structure of the complex between LUSH and alcohol, and clarified that Thr is a key residue involved in ligand interaction. According to the structures of odorant binding protein CquiOBP1 and MOP of Culex quinquefasciatus, Mao et al (2010) discovered that instead of hydrogen bonds, the interaction between protein and ligand was driven by van der Waals forces and hydrophobic interactions. Based on the structure between the odorant binding protein HoblOBP2 of Holotrichia oblita and ethyl benzenecarboxylate, Zhuang et al (2013) discovered that this protein-ligand complex involved both van der Waals forces and hydrophobic interactions. High-resolution structural data describing the complex between the pheromone binding protein of Cyrtotrachelus buqueti and an odor molecule is unavailable, and information about the mode of action of this protein remains unresolved
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