Fig. 4: ECL regions confer NbE binding selectivity.
From: Structural basis of μ-opioid receptor targeting by a nanobody antagonist
a Superposition of the inactive state of the NbE-bound µOR (blue), inactive δOR (green, PDB: 4EJ4), and inactive κOR (brown, PDB: 4DJH) with ECL2 and ECL3 indicated. b Binding interface of different ECL2 regions (murine µOR, murine δOR, and human κOR) with NbE. For comparison, the δOR and κOR have been superimposed onto the µOR. Q212ECL2 is unique to the µOR. c Binding interface of TM7 and ECL3 regions from the µOR, δOR, and κOR with NbE. For comparison, the δOR and κOR have been superimposed onto the TM7 and ECL3 regions of the µOR. Most interface residues differ between the different receptor subtypes. Color-coded as in (a). d NbE binding to the cells expressing wild-type (wt) µOR and ECL mutants (gated for similar receptor surface levels using anti-FLAG M1-AF647). NbE binding to wt µOR was normalized to 100%. µOR-KRQL-A mutant: K209, R211, Q212 and L219 substituted by alanine, E310A mutant: E310 substituted by alanine. µOR-KRQL-A & E310A: both sets of mutations combined. N = 5, mean ± SEM. **P = 0.0012 (ECL2), 0.0047 (ECL3), 0.0010 (ECL2&3) by ordinary one-way ANOVA. e NbE binding to cells expressing δOR mutants (gated for similar receptor surface levels using anti-FLAG M1-AF647). NbE binding to wt µOR was normalized to 100%. The three δOR mutants include δOR L300W7.35, a triple δORD193Q, M199T, L300W mutant, and a δOR mutant with the entire ECL3 and distal parts of TM7 substituted by µOR residues (δOR287-300-µOR-306-318). δOR wt: N = 5, δOR mutants: N = 3, mean ± SEM. **P = 0.0011, ****P = < 0.0001, n.s. = 0.8998 by ordinary one-way ANOVA. In all panels, N indicates the number of independent experiments. Source data are provided as a Source Data file.
