Ligand recognition mechanism of the human relaxin family peptide receptor 4 (RXFP4)

Relaxin family peptide receptor 4 (RXFP4) regulates pleiotropic biological processes. Here, authors report cryo-EM structures revealing the ligand-binding modes and key determinants of peptidomimetic agonism and subtype selectivity Members of the insulin superfamily regulate pleiotropic biological processes through two types of target-specific but structurally conserved peptides, insulin/insulin-like growth factors and relaxin/insulin-like peptides. The latter bind to the human relaxin family peptide receptors (RXFPs). Here, we report three cryo-electron microscopy structures of RXFP4-G(i) protein complexes in the presence of the endogenous ligand insulin-like peptide 5 (INSL5) or one of the two small molecule agonists, compound 4 and DC591053. The B chain of INSL5 adopts a single alpha-helix that penetrates into the orthosteric pocket, while the A chain sits above the orthosteric pocket, revealing a peptide-binding mode previously unknown. Together with mutagenesis and functional analyses, the key determinants responsible for the peptidomimetic agonism and subtype selectivity were identified. Our findings not only provide insights into ligand recognition and subtype selectivity among class A G protein-coupled receptors, but also expand the knowledge of signaling mechanisms in the insulin superfamily.

Automated summary

The authors reveal the ligand-binding modes and key determinants of peptidomimetic agonism and subtype selectivity through cryo-EM structures. This study provides insights into ligand recognition and subtype selectivity among class A G protein-coupled receptors, and expands the knowledge of signaling mechanisms in the insulin superfamily.