Activity of FGF19 chimeric proteins. A, schematic diagram
showing FGF19, -21, -23, and two FGF19 chimeric proteins. In FGF19–21C,
the FGF19 C-terminal region is replaced with that of FGF21. In
FGF19–23C, the FGF19 C-terminal region is replaced with that of FGF23.
B, ERK1/2 phosphorylation in HEK293 cells transfected with α or
βKlotho. FGF19–21C fails to activate ERK phosphorylation in HEK293
cells transfected with αKlotho, and FGF19–23C did not activate
cells transfected with βKlotho. C, in the pull-down assay, FGF19
requires either heparin, αKlotho, or βKlotho to bind to FGFR4.
FGF19–21C did not bind to FGFR4 in the presence of αKlotho, and
FGF19–23C did not bind to FGFR4 in the presence of βKlotho.
R4 indicates reactions containing FGFR4, ctl indicates
reactions with no FGFR added. D, solid-phase binding assay measuring
the direct interaction between FGF molecules and α or βKlotho.