Structure-Function Prediction of Insect Odorant Binding Proteins

Tzotzos, George T. (2013). Structure-Function Prediction of Insect Odorant Binding Proteins. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000f0e7

Abstract

This study concerns the application of bioinformatic tools for the elucidation of the biological function of insect general odorant and pheromone binding proteins (GOBPs / PBPs). These proteins are thought to function as transporters of volatile odorant molecules to olfactory receptors (ORs) situated in olfactory receptor neurons (ORNs) in insect antennae. Activation of ORNs by the odorant molecules gives rise to action potentials resulting in spatially defined patterns of glomerular activity in the brain, odour discrimination and concomitant behavioural response of the insect. The extent to which OBPs are critical for olfactory discrimination remains unclear. Numerous hypotheses have been postulated regarding the ability of OBPs to discriminate specific odorants and/or pheromones as well as their playing a role in the activation of odorant-responsive chemosensory neurons, in functioning as selective filters in odour recognition or participating in signal termination by inactivating odorant molecules. In silico binding studies of ligands and pheromones on OBPs derived from crystallographic studies or de novo homology modelling have been conducted primarily by docking and molecular dynamic (MD) simulations. It is shown that results obtained from such studies can provide useful insights and testable hypotheses with regard to the biochemical function of OBPs. Docking and MD simulations corroborate experimental evidence that the B. mori general odorant binding protein (BmorGOBP2) has considerably higher affinity than the B. mori pheromone binding protein (BmorPBPI) for the pheromonal components bombykol and bombykal and predict that this is also true for the modelled M. sexta proteins (MsexGOBP2 and MsexPBP1). In addition, steered molecular dynamics (SMD) simulations predict ligand entry and exit pathways into and out of BmorGOBP2. In addition, docking and molecular dynamics (MD) simulations with the highly homologous odorant binding proteins from A. gambiae (AgamOBP1), A. aegypti (AaegOBP1) and C. quinquefasciatus (CguiOBP1) provide evidence of differential capacity of these proteins to select ligands with specific structural characteristics.