Molecular Simulation Of The Odorant Binding Protein DhelOBP21 Of Insect Dastarcus Helophoroide

Olfactory system is highly tuned to perceive various chemical signals in the outward, which is vital for the feeding, calling behavior, risk-avoiding, reproduction and alert of the organisms. During the recognition and binding of the odors, the Odorant binding proteins(OBPs) is the first role in detection, binding, discrimination and transition of the volatiles. Then those volatiles are transported to the downstream proteins, such as olfactory receptors(ORs), and lead to olfactory perception finally. Hence the study of the interaction mechanism of the OBPs and volatiles is of significant importance.Herein, the three-dimensional structure of the DhelOBP21 was available via homology modelling. And further investigation suggested that the DhelOBP21 is a typical Minus-C OBP which contains 4 conserved CYSs forming two S-S bridges and stabilizing the conformation of the protein, and its relatively hydrophobic pocket is favorable for those hydrophobic volatiles. Then the primary binding modes of the DhelOBP21 and the 18 ligands were achieved through molecular docking and those complexes were used for the following molecular dynamics.Moreover, by the Conventional Molecular Dynamics and Constant pH Molecular Dynamics, we first observed the transition between Random Coil and Alpha Helix of the N-terminus of the DhelOBP21. Accordingly, we proposed a new hypothesis: the Minus-C OBPs undergo a both pH and ligand dependent conformation change. When the pH increase from 5.0 to 7.0, the N-terminus of the OBPs transform into a regular Alpha helix and move towards the pocket, which is beneficial to the binding and transportation of the volatiles; While when the p H decrease from 7.0 to 5.0, the N-terminus of the OBPs transform into Random Coil and move away from the pocket, which is favorable for the release of volatiles.Besides, the free energy contributions of some pocket residues against the 18 ligands are always very huge, these residues are, hence, defined as ‘Fundamental Residues’ which may determine the promiscuity of the OBPs. While the contribution of some other pocket residues vary among different ligands, then they are defined as ‘Selective Residues’ which may be involved in the selectivity of the OBPs.In this thesis a new hypothesis about the interaction mechanism of the Minus-C OBPs and volatiles was proposed. And the promiscuity and selectivity of the OBPs against the volatiles were also put forward from the protein perspective, which could provide new insight and comprehension of several problems such as the olfactory recognition and host location of the insects.