Rewiring Receptor Activation: Mechanistic Insights into Toggle Switch Modulation by 25CN-NBx Compounds

The development of new treatments for neuropsychiatric disorders relies on a deeper understanding of the molecular mechanisms behind psychedelic compounds, particularly how they differentiate between hallucinogenic and antidepressant effects. In this study, we explore by molecular dynamics simulations a series of 25CN-NBx compounds bound to the 5-HT_2A receptor. The simulations uncover that bulky substitutions on the <i>N</i>-benzyl ring cause a significant shift in the position of W336, a key toggle switch residue known to influence receptor activation and thought to play a crucial role in mediating psychedelic signaling. This result is confirmed through potential of mean force calculations along the toggle switch's dihedral angle. End-state free energy calculations align closely with experimental data, showing that 25CN-NB-2-OH-3-Me and 25CN-NB-2-OH-5-MeO have the highest and lowest affinities, respectively, for the 5-HT_2A receptor. Further analysis indicates that when W336 adopts its negative dihedral state, it establishes stronger van der Waals interactions, stabilizing its contacts with residues F332 and I163─key players previously linked to receptor activation. Our findings provide a framework for understanding receptor activation and can be extended to other G protein-coupled receptors where the toggle switch is central to signal activation.