A parallel semisynthetic approach for structure-activity relationship studies of peptide YY

G Protein Preassembly Rescues Efficacy of W6.48 Toggle Mutations in Neuropeptide Y2 Receptor

Ligand binding and pathway-specific activation of G protein-coupled receptors is currently being studied with great effort. Individual answers may depend on the nature of the ligands and the effector pathway. Recently, we have presented a detailed model of neuropeptide Y bound to the Y2R. Accordingly, the C-terminal part of the peptide binds deeply in the transmembrane bundle and brings the side chain of the most essential Y36 in close proximity to W6.48 Here, we investigate the role of this interaction for ligand binding and activation of this receptor. BRET sensors were used for detailed investigation of effector coupling and led to the identification of preassembly of the Y2R-Gi complex. It further confirmed ligand-dependent recruitment of arrestin3. Using equally sensitive readouts for Gi activation and arrestin recruitment as well as quantification with operational models of agonism allowed us to identify a strong inherent bias for Gi activation over arrestin3 recruitment for the wild-type receptor. By systematic mutagenesis, we found that W6.48 does not contribute to the binding affinity, but acts as an allosteric connector to couple ligand binding to Gi activation and arrestin3 recruitment. However, even mutagenesis to a small threonine did not lead to a complete loss of signaling. Interestingly, signaling was restored to wild-type levels by ligands that contain a naphthylalanine as the C-terminal residue instead of Y36 Steric and polar contributions of W6.48 for the activation of the receptor are discussed in the context of different mechanisms of G protein coupling and arrestin recruitment.

A Deep Hydrophobic Binding Cavity is the Main Interaction for Different Y2 R Antagonists

The neuropeptide Y₂ receptor (Y₂ R) is involved in various pathophysiological processes such as epilepsy, mood disorders, angiogenesis, and tumor growth. Therefore, the Y₂ R is an interesting target for drug development. A detailed understanding of the binding pocket could facilitate the development of highly selective antagonists to study the role of Y₂ R in vitro and in vivo. In this study, several residues crucial to the interaction of BIIE0246 and SF-11 derivatives with Y₂ R were investigated by signal transduction assays. Using the experimental results as constraints, the antagonists were docked into a comparative structural model of the Y₂ R. Despite differences in size and structure, all three antagonists display a similar binding site, including a deep hydrophobic cavity formed by transmembrane helices (TM) 4, 5, and 6, as well as a hydrophobic patch at the top of TM2 and 7. Additionally, we suggest that the antagonists block Q^3.32 , a position that has been shown to be crucial for binding of the amidated C terminus of NPY and thus for receptor activation.

Unwinding of the C-Terminal Residues of Neuropeptide Y is critical for Y₂ Receptor Binding and Activation

Despite recent breakthroughs in the structural characterization of G-protein-coupled receptors (GPCRs), there is only sparse data on how GPCRs recognize larger peptide ligands. NMR spectroscopy, molecular modeling, and double-cycle mutagenesis studies were integrated to obtain a structural model of the peptide hormone neuropeptide Y (NPY) bound to its human G-protein-coupled Y2 receptor (Y2R). Solid-state NMR measurements of specific isotope-labeled NPY in complex with in vitro folded Y2R reconstituted into phospholipid bicelles provided the bioactive structure of the peptide. Guided by solution NMR experiments, it could be shown that the ligand is tethered to the second extracellular loop by hydrophobic contacts. The C-terminal α-helix of NPY, which is formed in a membrane environment in the absence of the receptor, is unwound starting at T(32) to provide optimal contacts in a deep binding pocket within the transmembrane bundle of the Y2R.

Design and Synthesis of Peptide YY Analogues with C-terminal Backbone Amide-to-Ester Modifications

Peptide YY (PYY) is a gut hormone that activates the G protein-coupled neuropeptide Y (NPY) receptors, and because of its appetite reducing actions, it is evaluated as an antiobesity drug candidate. The C-terminal tail of PYY is crucial for activation of the NPY receptors. Here, we describe the design and preparation of a series of PYY(3-36) depsipeptide analogues, in which backbone amide-to-ester modifications were systematically introduced in the C-terminal. Functional NPY receptor assays and circular dichroism revealed that the ψ(CONH) bonds at positions 30-31 and 33-34 are particularly important for receptor interaction and that the latter is implicated in Y2 receptor selectivity.