A structural feature of the non-peptide ligand interactions with mice mu-opioid receptors

Molecular insights into the interaction of hemorphin and its targets

Hemorphins are atypical endogenous opioid peptides produced by the cleavage of hemoglobin beta chain. Several studies have reported the therapeutic potential of hemorphin in memory enhancement, blood regulation, and analgesia. However, the mode of interaction of hemorphin with its target remains largely elusive. The decapeptide LVV-hemorphin-7 is the most stable form of hemorphin. It binds with high affinity to mu-opioid receptors (MOR), angiotensin-converting enzyme (ACE) and insulin-regulated aminopeptidase (IRAP). In this study, computational methods were used extensively to elucidate the most likely binding pose of mammalian LVV-hemorphin-7 with the aforementioned proteins and to calculate the binding affinity. Additionally, alignment of mammalian hemorphin sequences showed that the hemorphin sequence of the camel harbors a variation - a Q > R substitution at position 8. This study also investigated the binding affinity and the interaction mechanism of camel LVV-hemorphin-7 with these proteins. To gain a better understanding of the dynamics of the molecular interactions between the selected targets and hemorphin peptides, 100 ns molecular dynamics simulations of the best-ranked poses were performed. Simulations highlighted major interactions between the peptides and key residues in the binding site of the proteins. Interestingly, camel hemorphin had a higher binding affinity and showed more interactions with all three proteins when compared to the canonical mammalian LVV-hemorphin-7. Thus, camel LVV-hemorphin-7 could be explored as a potent therapeutic agent for memory loss, hypertension, and analgesia.

Mu-Opioid receptor biased ligands: A safer and painless discovery of analgesics?

Biased activation of G-protein-coupled receptors (GPCRs) is shifting drug discovery efforts and appears promising for the development of safer drugs. The most effective analgesics to treat acute pain are agonists of the μ opioid receptor (μ-OR), a member of the GPCR superfamily. However, the analgesic use of opioid drugs, such as morphine, is hindered by adverse effects. Only a few μ-OR agonists have been reported to selectively activate the G_i over β-arrestin signaling pathway, resulting in lower gastrointestinal dysfunction and respiratory suppression. Here, we discuss the strategies that led to the development of biased μ-OR agonists, and potential areas for improvement, with an emphasis on structural aspects of the ligand-receptor recognition process.