6BD4:
reference: Crystal structure of the Frizzled 4 receptor in a ligand-free state., Yang S, Wu Y, Xu TH, de Waal PW, He Y, Pu M, Chen Y, DeBruine ZJ, Zhang B, Zaidi SA, Popov P, Guo Y, Han GW, Lu Y, Suino-Powell K, Dong S, Harikumar KG, Miller LJ, Katritch V, Xu HE, Shui W, Stevens RC, Melcher K, Zhao S, Xu F, Nature. 2018 Aug;560(7720):666-670. doi: 10.1038/s41586-018-0447-x. Epub 2018 Aug, 22. PMID: 30135577

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