Structural insights into ligand recognition by the pleiotropic odorant-binding protein AgamOBP9

Area of Science:

• Structural biology
• Molecular entomology
• Vector control

Background:

• Mosquito odorant-binding proteins (OBPs) are crucial for olfaction and potential vector control targets.
• Some OBPs exhibit non-olfactory functions, indicating broader roles beyond olfaction.
• AgamOBP9 from Anopheles gambiae is a pleiotropic OBP with largely uninvestigated functions.

Purpose of the Study:

• To elucidate the structural basis of ligand binding by the pleiotropic mosquito OBP, AgamOBP9.
• To investigate the binding interactions of plant-derived molecules with AgamOBP9.
• To explore the potential for AgamOBP9 to bind diverse molecules, suggesting non-olfactory roles.

Main Methods:

• X-ray crystallography to determine the structures of AgamOBP9 in complex with n-butyl cinnamate, methyl eugenol (ME), and p-menthane-3, 8-diol (PMD).
• Fluorescence competitive binding assays and binding free-energy calculations to quantify ligand affinities.
• Differential scanning calorimetry and molecular dynamics simulations to assess protein conformational flexibility.

Main Results:

• AgamOBP9 binds n-butyl cinnamate and ME with micromolar affinity, while PMD shows weak binding.
• The protein possesses an extended internal cavity with two distinct ligand-binding regions, one pre-ordered and one at the entrance.
• Ligand binding, particularly PMD at the entrance, induces conformational changes, suggesting dynamic structural adaptability.

Conclusions:

• AgamOBP9 exhibits a flexible binding site capable of accommodating diverse molecules, including potential fatty acids.
• The structural plasticity of AgamOBP9 supports its proposed pleiotropic functions beyond olfaction.
• Understanding AgamOBP9's ligand recognition mechanisms can inform the development of novel OBP-targeting control strategies.