Fig. 1.

Design and characterization of FGF19 variants. (A) A hypothetical 2:2:2:2 FGF19-FGFR1c-KLB-HS dimeric complex was constructed by superimposing structures of FGF19 alone (PDB ID code: 2P23) and of KLB in complex with the C-terminal tail of FGF19 (FGF19^CT) (PDB ID code: 6NFJ) onto a dimeric model of a FGF23-FGFR1c-αKlotho-HS dimer (PDB ID code: 5W21). FGF19, FGFR1c, and KLB are shown as cyan, light blue, and purple cartoons, respectively; HS is shown as sticks with carbon, nitrogen, oxygen, and sulfur colored in green, blue, red, and yellow, respectively. (B) Close-up view of interfaces between FGF19 and FGFR (Left), FGF19 and HS (Center), and FGF19 and KLB (Right). In Left, Tyr-115 of FGF19 and Val-316 of FGFR1c are shown as surfaces to highlight their hydrophobic interaction. At Center, the side chain of Lys-149 of FGF19 which engages in hydrogen bonds with HS is shown as sticks. Right shows multiple intramolecular hydrogen bonds mediated by Asp-198 that facilitate FGF19^CT conformation, thereby contributing to KLB binding. In Center and Right, black dashed lines denote hydrogen bonds. (C–F) Representative SPR sensorgrams of binding of FGF19^WT and FGF19 variants to the ligand-binding domains of FGFR4 (C) and FGFR1 (D), and to HS (E) and KLB (F). Equilibrium dissociation constants (K_d values) were derived from saturation binding curves.