Conformational Changes Induced By Phenylalanine Substitution of Serine 129 Are Associated with Loss of Function in Fibroblast Growth Factor23/S129F

Presentation Number: SAT 345
Date of Presentation: April 1st, 2017

Said M Shawar*, Ahmad R Ramadan and Shazia Sabir
Arabian Gulf University, Manama, Bahrain

Abstract

Hyperphosphatemic familial tumoral calcinosis (HFTC, OMIM 211900) is a rare autosomal recessive disorder. It is characterized by hyperphosphatemia, normal or elevated serum 1,25-dihydroxyvitamin D, and ectopic calcifications. Eight loss-of-function mutations in the amino fragment (N-fragment) of fibroblast growth factor-23 (FGF23) between residues 41-129 are implicated in causing HFTC. Recently, we established that high levels of inactive FGF23/S129F are present in the circulation of HFTC patients. To test whether phenylalanine substitution of serine 129 causes a 3D structural change in the hormone, we employed computer simulation modeling based on the crystal structure of human wild-type (WT) FGF23 (2P39). Our simulation data indicated that the substitution causes a visible structural change between the WT and the mutant hormone. We confirmed our computer simulation results using antibodies that recognize linear or conformational epitopes on the hormone. WT FGF23 from healthy individuals or transfected HEK293 cells were recognized by a monoclonal antibody that recognizes a discontinuous epitope on the native hormone. In contrast, the mutant hormone from HFTC patients or transfected HEK293 cells failed to bind the same monoclonal. Alternatively, affinity purified goat polyclonal antibodies generated against human FGF23 peptide 51-69 recognized all species of WT FGF23 and mutant hormone. Our results indicate that the inactivity by FGF23/S129F is associated with a conformational change at the fibroblast growth factor receptor/α-Klotho complex.

 

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