FGF23 contains two distinct high-affinity binding sites enabling bivalent interactions with α-Klotho.

Area of Science:

• Endocrinology
• Molecular Biology
• Metabolic Regulation

Background:

• Fibroblast growth factor (FGF) 23 is a key hormone regulating phosphate and vitamin D metabolism.
• FGF23 signals through a complex involving α-Klotho (KLA) and FGF receptors (FGFRs).

Purpose of the Study:

• To investigate the structural and functional basis of FGF23 binding to KLA.
• To explore the potential of targeting the FGF23-KLA interaction for therapeutic purposes.

Main Methods:

• Analysis of FGF23 C-terminal repeats (R1 and R2) for KLA binding.
• Biochemical assays to measure binding affinity and receptor activation (FGFR1, MAPK).
• Total internal reflection fluorescence microscopy to visualize KLA-FGFR dimerization on cell surfaces.

Main Results:

• FGF23's C-terminal tail contains two functional KLA binding repeats (R1 and R2).
• Both single-repeat (FGF23-R1, FGF23-R2) and wild-type FGF23 (FGF23-WT) bind KLA with similar affinity and activate signaling.
• FGF23-WT functions as a bivalent ligand, promoting KLA-FGFR dimerization and activation.
• Disulfide bond formation in FGF23-WT is not essential for KLA binding or signaling.

Conclusions:

• FGF23 utilizes a bivalent binding mechanism with KLA through its R1 and R2 repeats.
• Understanding this interaction provides insights into FGF23's metabolic regulatory functions.
• An engineered KLA-Fc fusion protein acts as an FGF23 antagonist, suggesting a novel therapeutic strategy for FGF23-related disorders.