4L6R:
reference: Structure of the human glucagon class B G-protein-coupled receptor., Siu FY, He M, de Graaf C, Han GW, Yang D, Zhang Z, Zhou C, Xu Q, Wacker D, Joseph JS, Liu W, Lau J, Cherezov V, Katritch V, Wang MW, Stevens RC, Nature. 2013 Jul 25;499(7459):444-9. doi: 10.1038/nature12393. Epub 2013 Jul 17. PMID: 23863937

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