Binding of agonist WAY-267,464 and antagonist WAY-methylated to oxytocin receptor probed by all-atom molecular dynamics simulations

Non-peptide ligands of oxytocin receptor (OTR) have promising potentialities as therapeutic agents with improved pharmacological properties. WAY-267,464 is a non-peptide agonist which loses its agonist activity when its resorcinol moiety is methylated, yielding a partial antagonist (denoted here, WAY-Methylated). This study attempts to rationalize these opposing activities by comparative analyses of structural dynamicsof OTR in complex with these ligands.Glide extra precision (XP) docking with and without positional constraints was employed to probe alternative binding poses of both WAY-267,464 and WAY-Methylated. The more preferred configuration of each system was subjected to an extended 2 μs MD simulation and the physics-based Molecular Mechanics-Generalized Born Surface Area (MM-GBSA) binding energy was used to rank the complexes with improved accuracy, in addition to empirical-based Glide docking score. Network analysis was performed, and the identified critical residues were cross-referenced with the experimental mutagenesis data.The added methyl groups in the antagonist WAY-Methylated enhanced hydrophobicity, resulting in a flipped binding pose deeper in the binding pocket. Interestingly, OTR responded to the methylation by stabilizing the initial inactive conformation, decreasing fluctuations and increasing the overall secondary structural composition. Conversely, the agonist WAY-267,464 produced larger fluctuations to allow the receptor to change from the default inactive state to a state of partial activation. These transitions were further supported by the identified critical residues overlapping with experimental mutagenesis data.These findings provide insights into the activation mechanism of OTR by WAY-267.464 and its antagonism by WAY-Methylated.