Structural and biosynthetic characterization of the fibroblast growth factor receptor 3 (FGFR-3) protein

Recently an additional member of the fibroblast growth factor receptor family, FGFR-3, was isolated. In this report, the structure and biosynthesis of the FGFR-3 protein product are investigated. In vitro transcription and translation of the three immunoglobulin-like domain form of FGFR-3 demonstrated the primary translation product to be approximately 97 kDa. However when analysed in COS-1 cells, this form of the receptor directed the expression of three polypeptides with apparent molecular weights of 97 kDa, 125 kDa and 135 kDa. Pulse-chase analysis, treatment of the cells with N-linked glycosylation inhibitors and digestion of these proteins with endoglycosidases demonstrated that the difference in molecular weights was the result of varying degrees of glycosylation. The 97 kDa protein was determined to be a non-glycosylated, cytoplasmic protein, whereas the 125 kDa protein was found to be a membrane-associated glycoprotein that is the biosynthetic precursor of the mature 135 kDa glycoprotein.