Determinants of Orexin Receptor Binding and Activation-A Molecular Dynamics Study

Area of Science:

• Pharmacology
• Neuroscience
• Computational Chemistry

Background:

• The orexin system plays a crucial role in regulating sleep-wake cycles and appetite.
• Understanding orexin receptor (OX₂) activation mechanisms is vital for developing targeted therapeutics.
• Previous studies proposed binding modes for orexin-A, but their stability and functional implications remain unclear.

Purpose of the Study:

• To assess the stability of proposed orexin-A binding modes within the OX₂ receptor.
• To investigate the influence of cholesterol on orexin receptor dynamics and ligand interactions.
• To identify key molecular interactions governing OX₂ receptor activation and inactivation.

Main Methods:

• Extensive molecular dynamics (MD) simulations totaling 36 microseconds.
• Simulations included an unliganded OX₂ receptor and complexes with orexin-A, suvorexant (antagonist), and Nag26 (agonist).
• Systems were modeled in both pure POPC and 25% cholesterol-POPC membranes.

Main Results:

• A stable binding mode for the C-terminus of orexin-A within the OX₂ receptor was identified.
• Distinct interactions were observed that may promote receptor activation.
• Specific interactions were also found to stabilize the inactive state of the OX₂ receptor.

Conclusions:

• The C-terminal binding of orexin-A represents a stable conformation within the OX₂ receptor.
• These findings provide a structural basis for understanding orexin receptor activation and antagonism.
• The study offers insights into designing novel modulators of the orexin system for therapeutic applications.