Rational design of a Kappa opioid receptor peptide agonist with attenuated β-arrestin signaling.

Difelikefalin is an FDA-approved κ-opioid receptor (KOR) peptide agonist used to treat chronic pruritus. However, as a balanced agonist that activates both G protein and β-arrestin pathways, difelikefalin remains associated with undesirable side effects linked to β-arrestin signaling. Here, we report the cryo-EM structure of the difelikefalin-KOR-Gi complex, identifying Y3207.43 as a key residue that is critical for signaling bias. Guided by this structural insight, we engineer beta01, a β-amino acid-substituted analog with potent G protein activation but minimal β-arrestin recruitment. In mouse models, beta01 retains robust antinociceptive and antipruritic efficacy while significantly reducing sedation and anxiety-like behaviors. Structural, molecular dynamics simulations and 2D 13C-Met NMR analyses further reveal beta01 stabilizes a unique KOR conformation with an expanded intracellular cavity that disfavors β-arrestin binding. This work establishes a rational structure-based framework for designing safer and more effective GPCR-targeted therapeutics.