Molecular elements in FGF19 and FGF21 defining KLB/FGFR activity and specificity

Area of Science:

• Biochemistry
• Endocrinology
• Metabolic Signaling

Background:

• Fibroblast Growth Factor (FGF) 19 and FGF21 signal through FGF receptors (FGFRs) and the co-receptor βKlotho (KLB).
• Variations exist in the C-terminal sequences of FGF19 and FGF21, crucial for receptor binding and activity.
• Understanding these sequence differences is key to designing targeted agonists and antagonists.

Purpose of the Study:

• To investigate the functional impact of C-terminal sequence variations in FGF19 and FGF21.
• To identify C-terminal fragments that can act as potent antagonists of FGF19 and FGF21 signaling.
• To explore the potential for designing enhanced FGF agonists based on these findings.

Main Methods:

• Utilized in vitro assays to screen for C-terminal protein fragments inhibiting KLB-mediated FGF19/21 signaling.
• Employed peptide-based Alanine scanning to identify key residues for bioactivity.
• Chemically optimized antagonistic peptides and assessed a modified FGF21 in cell culture and obese mouse models.

Main Results:

• Short C-terminal peptides of FGF19 and FGF21 demonstrated potent inhibition of hormone activity in vitro and in vivo.
• Conserved structural determinants for KLB binding were observed despite sequence variations.
• A single C-terminal amino acid in FGF19 influenced FGFR1 and FGFR4 activity.
• An optimized FGF21 chimera exhibited enhanced agonistic potency and improved metabolic outcomes in obese mice.

Conclusions:

• Short C-terminal peptides can effectively bind KLB and antagonize FGF19/21 actions.
• High sequence conservation in key KLB-binding residues was maintained.
• A modified FGF21 with an optimized C-terminus acted as a super-agonist, conferring metabolic benefits in obese mice.