Fig. 1

The structure and post-translational modification of FGF23 protein. FGF23 protein is produced as a peptide with 251 amino acids. FGF23 with 227 amino acids is secreted after the cleavage of a signal peptide with 24 amino acids. A part of FGF23 protein is cleaved between Arg¹⁷⁹ and Ser¹⁸⁰ into inactive N-terminal and C-terminal fragments before or during the process of secretion. O-glycosylation of Thr¹⁷⁸ by GalNac-T3, a gene product of GALNT3, inhibits this cleavage and increases full-length FGF23. Phosphorylation of Ser¹⁸⁰ inhibits O-glycosylation by GALNT3 and enhances the processing of FGF23 protein. GalNac-T3: polypeptide N-acetylgalactosaminyltransferase 3; GALNT3: polypeptide N-acetylgalactosaminyltransferase 3