Identification and characterization of an intracellular protein complex that binds fibroblast growth factor-2 in bovine brain

The fibroblast growth factor (FGF) family is composed of polypeptides with sequence identity which signal through transmembrane tyrosine kinase recept ors. We report here the purification from bovine brain microsomes of an FGF -2-binding complex composed of three proteins of apparent molecular masses 150 kDa, 79 kDa and 46 kDa, Only the 150 kDa and 79 kDa proteins bound FGF- 2 in cross-linking and ligand-blotting experiments. Binding of FGF-2 to p79 is enhanced in the presence of calcium. Peptide sequences allowed the iden tification of p150 and the cloning of the cDNAs encoding p79 and p46. The d educed amino acid sequence of p79 reveals high similarity to those of gastr in-binding protein and mitochondrial enoyl-CoA hydratase/hydroxyacyl-CoA de hydrogenase. p46 is similar to mitochondrial ketoacyl-CoA thiolase. Stable transfection of FR3T3 rat fibroblast cells with p79 cDNA analysed by electr on microscopy following immunolabelling of ultra-thin cryosections revealed a localization of p79 in the secretory pathway, mainly in the endoplasmic reticulum and the Golgi region, where it is specifically associated with th e molecular chaperone calnexin, In vivo a protein similar to the Golgi prot ein MG-160 forms a complex with FGF-2 and p79.