In drug design and discovery,binding affinity and selectivity are two basic properties of a drug candidate.Opioid receptors (ORs) are the main targets of strong analgesics.Like some other class A members of G-protein-coupled receptors (GPCRs),ORs exhibit complex selectivity on their ligands.The diversity of binding activity and selectivity among opioids has deeply attracted researchers for a long time.To investigate the subtype selectivity of μ,δ and K ORs in detail,using the K-selective antagonist JDTic as a probe,we performed a series of computational simulations,including molecular dynamics and metadynamics,on JDTic-μ/δ/K-OR complexes.From the simulations,we found that the decisive factor of JDTic selectivity on the μ-subtype was the 2.63 position,which affected the efficacy of JDTic through changing the dynamics of the Q2.60 residue.In addition to the 2.63-position residue,the 7.35 position was the other crucial aspect of JDTic selectivity for the δ-subtype.Based on the results,we suggest a new concept,the "message-address-efficacy" hypothesis,to explain the relationships among the affinity,selectivity and function between ORs and opioids.Thus,all the detailed dynamics of JDTic-bound ORs might be helpful to deeply understand the subtype selectivity and binding mechanisms of other GPCRs.