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Structure of the mu opioid receptor bound to the antagonist nanobody NbE
Structural highlights
FunctionOPRM_MOUSE Receptor for endogenous opioids such as beta-endorphin and endomorphin. Agonist binding to the receptor induces coupling to an inactive GDP-bound heterotrimeric G-protein complex and subsequent exchange of GDP for GTP in the G-protein alpha subunit leading to dissociation of the G-protein complex with the free GTP-bound G-protein alpha and the G-protein beta-gamma dimer activating downstream cellular effectors. The agonist- and cell type-specific activity is predominantly coupled to pertussis toxin-sensitive G(i) and G(o) G alpha proteins, GNAI1, GNAI2, GNAI3 and GNAO1 isoforms Alpha-1 and Alpha-2, and to a lesser extend to pertussis toxin-insensitive G alpha proteins GNAZ and GNA15. They mediate an array of downstream cellular responses, including inhibition of adenylate cyclase activity and both N-type and L-type calcium channels, activation of inward rectifying potassium channels, mitogen-activated protein kinase (MAPK), phospholipase C (PLC), phosphoinositide/protein kinase (PKC), phosphoinositide 3-kinase (PI3K) and regulation of NF-kappa-B. Also couples to adenylate cyclase stimulatory G alpha proteins. The selective temporal coupling to G-proteins and subsequent signaling can be regulated by RGSZ proteins, such as RGS9, RGS17 and RGS4. Phosphorylation by members of the GPRK subfamily of Ser/Thr protein kinases and association with beta-arrestins is involved in short-term receptor desensitization. Beta-arrestins associate with the GPRK-phosphorylated receptor and uncouple it from the G-protein thus terminating signal transduction. The phosphorylated receptor is internalized through endocytosis via clathrin-coated pits which involves beta-arrestins. The activation of the ERK pathway occurs either in a G-protein-dependent or a beta-arrestin-dependent manner and is regulated by agonist-specific receptor phosphorylation. Acts as a class A G-protein coupled receptor (GPCR) which dissociates from beta-arrestin at or near the plasma membrane and undergoes rapid recycling. Receptor down-regulation pathways are varying with the agonist and occur dependent or independent of G-protein coupling. Endogenous ligands induce rapid desensitization, endocytosis and recycling. Heterooligomerization with other GPCRs can modulate agonist binding, signaling and trafficking properties. Involved in neurogenesis. Isoform 9 is involved in morphine-induced scratching and seems to cross-activate GRPR in response to morphine.[1] [2] [3] [4] [5] [6] Publication Abstract from PubMedThe mu-opioid receptor (muOR), a prototypical member of the G protein-coupled receptor (GPCR) family, is the molecular target of opioid analgesics such as morphine and fentanyl. Due to the limitations and severe side effects of currently available opioid drugs, there is considerable interest in developing novel modulators of muOR function. Most GPCR ligands today are small molecules, however biologics, including antibodies and nanobodies, are emerging as alternative therapeutics with clear advantages such as affinity and target selectivity. Here, we describe the nanobody NbE, which selectively binds to the muOR and acts as an antagonist. We functionally characterize NbE as an extracellular and genetically encoded muOR ligand and uncover the molecular basis for muOR antagonism by solving the cryo-EM structure of the NbE-muOR complex. NbE displays a unique ligand binding mode and achieves muOR selectivity by interactions with the orthosteric pocket and extracellular receptor loops. Based on a beta-hairpin loop formed by NbE that deeply inserts into the muOR and centers most binding contacts, we design short peptide analogues that retain muOR antagonism. The work illustrates the potential of nanobodies to uniquely engage with GPCRs and describes novel muOR ligands that can serve as a basis for therapeutic developments. Structural Basis of mu-Opioid Receptor-Targeting by a Nanobody Antagonist.,Yu J, Kumar A, Zhang X, Martin C, Raia P, Koehl A, Laeremans T, Steyaert J, Manglik A, Ballet S, Boland A, Stoeber M bioRxiv [Preprint]. 2023 Dec 7:2023.12.06.570395. doi: 10.1101/2023.12.06.570395. PMID:38106026[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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