We thank J.-P. Carralot (F. Hoffmann–La Roche) for help in antibody generation, C. Yoshioka and C. Lopez for assistance with data collection, M. Siegrist, G. Schmid, B. Rutten, D. Zulauf, S. Kueng (Roche Non-Clinical Biorepository) and R. Thoma for technical assistance with biomass and cell line generation. We also acknowledge N. Moriarty (Lawrence Berkeley National Laboratories) for help with generation of parameters for DAMGO and general advice for refinement of our model. The work is supported by NIH grant R37DA036246 (B.K.K., S.G. and G.S.) and NIH grant R01GM083118 (B.K.K.). Research reported in this publication was supported by the National Institute of General Medical Sciences of the National Institutes of Health under award number T32GM007276 (A.K.). The content is solely the responsibility of the authors and does not necessarily represent the official view of the National Institutes of Health. S.M. was supported by the Roche Postdoctoral Fellowship (RPF ID: 113). G.F.X.S. acknowledges the Swiss National Science Foundation for grants 310030_153145 and 310030B_17335 and long-term financial support from the Paul Scherrer Institute. B.K.K. is a Chan–Zuckerberg Biohub Investigator.

Reviewer information

Nature thanks L. Shi, D. Wacker and the other anonymous reviewer(s) for their contribution to the peer review of this work.