Three Amino Acid Residues Bind Corn Odorants to McinOBP1 in the Polyembryonic Endoparasitoid of Macrocentrus cingulum Brischke

Tofael Ahmed,Zhen-Ying Wang,Tian-Tao Zhang,Shu-Xiong Bai,Kang-Lai He,Eugene A Permyakov

doi:10.1371/journal.pone.0093501

Abstract

Odorant binding proteins (OBPs) play a central role in transporting odorant molecules from the sensillum lymph to olfactory receptors to initiate behavioral responses. In this study, the OBP of Macrocentrus cingulum McinOBP1 was expressed in Escherichia coli and purified by Ni ion affinity chromatography. Real-time PCR experiments indicate that the McinOBP1 is expressed mainly in adult antennae, with expression levels differing by sex. Ligand-binding experiments using N-phenyl-naphthylamine (1-NPN) as a fluorescent probe demonstrated that the McinOBP1 can bind green-leaf volatiles, including aldehydes and terpenoids, but also can bind aliphatic alcohols with good affinity, in the order trans-2-nonenal>cis-3-hexen-1-ol>trans-caryophelle, suggesting a role of McinOBP1 in general odorant chemoreception. We chose those three odorants for further homology modeling and ligand docking based on their binding affinity. The Val58, Leu62 and Glu130 are the key amino acids in the binding pockets that bind with these three odorants. The three mutants, Val58, Leu62 and Glu130, where the valine, leucine and glutamic residues were replaced by alanine, proline and alanine, respectively; showed reduced affinity to these odorants. This information suggests, Val58, Leu62 and Glu130 are involved in the binding of these compounds, possibly through the specific recognition of ligands that forms hydrogen bonds with the ligands functional groups.

Highlights

Olfaction is a finely tuned sense, essential for sensory assessment of the environment, which plays a crucial role for insects in foraging, host-seeking, mating, ovipositing and avoiding toxin substances
odorant receptors (ORs) are heterodimers comprised of highly variable odorant-binding subunits associated with one conserved co-receptor (OR83b) [8] and these are most widely expressed in the dendritic membranes of olfactory sensory neurons (OSNs) that are housed in sensory hairs called olfactory sensilla [9]
Coding and Sequence Analysis of McinOBP1 McinOBP1of the M. cingulum was obtained from the antennal cDNA library is a protein expressed in antennae

Summary

Introduction

Olfaction is a finely tuned sense, essential for sensory assessment of the environment, which plays a crucial role for insects in foraging, host-seeking, mating, ovipositing and avoiding toxin substances. Olfaction is mediated by specific olfactory sensory neurons, which project their dendrites into a lymphatic cavity where odorant binding proteins (OBPs) are present at high concentrations [1]. The major proteins involved in the selectivity and sensitivity of the insect olfactory system are odorant-binding proteins (OBPs) [2] and odorant receptors (ORs) [3]. The first step in the recognition of odorants are air-born small hydrophobic molecules mediated by OBPs [5,6] that are involved in odorant reception, where they bind, solubilize and deliver odorant molecules to ORs [2,7]. ORs are heterodimers comprised of highly variable odorant-binding subunits associated with one conserved co-receptor (OR83b) [8] and these are most widely expressed in the dendritic membranes of olfactory sensory neurons (OSNs) that are housed in sensory hairs called olfactory sensilla [9]

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Conclusion