G-protein-coupled receptors (GPCRs) are the most important signal transducers in higher eukaryotes. Despite considerable progress, the molecular basis of subtype-specific ligand selectivity, especially for peptide receptors, remains unknown. Here, by integrating DNP-enhanced solid-state NMR spectroscopy with advanced molecular modeling and docking, the mechanism of the subtype selectivity of human bradykinin receptors for their peptide agonists has been resolved. The conserved middle segments of the bound peptides show distinct conformations that result in different presentations of their N and C termini toward their receptors. Analysis of the peptide–receptor interfaces reveals that the charged N-terminal residues of the peptides are mainly selected through electrostatic interactions, whereas the C-terminal segments are recognized via both conformations and interactions. The detailed molecular picture obtained by this approach opens a new gateway for exploring the complex conformational and chemical space of peptides and peptide analogs for designing GPCR subtype-selective biochemical tools and drugs.

G蛋白偶联受体（GPCR）是高等真核生物中最重要的信号转导子。尽管取得了很大进展，但亚型特异性配体选择性的分子基础，特别是对肽受体的分子基础仍然未知。在这里，通过将DNP增强的固态NMR光谱与先进的分子建模和对接相结合，人类缓激肽受体对其肽激动剂的亚型选择性机制已得到解决。结合的肽的保守的中间区段显示出不同的构象，导致它们的N和C末端朝着它们的受体的不同呈现。对肽-受体界面的分析表明，肽的带电N末端残基主要是通过静电相互作用选择的，而C末端片段是通过构象和相互作用识别的。通过这种方法获得的详细分子图，为探索肽和肽类似物的复杂构象和化学空间，以设计GPCR亚型选择性生化工具和药物开辟了一条新途径。