TYPE-SPECIFIC ANTIBODIES TO THE PLATELET-DERIVED GROWTH-FACTOR RECEPTORS - ROLE IN ELUCIDATING THE STRUCTURAL AND FUNCTIONAL-CHARACTERISTICS OF RECEPTOR TYPES

Two types of platelet-derived growth factor receptors have been cloned and sequenced. Both are glycoproteins with similar molecular weights. We have earlier established the ligand binding specificity, ligand-induced dimerization, and kinase activation of these two receptor types [Bishayee et al. (1989) J. Biol. Chem. 264, 11699-11705; Kanakaraj et al. (1991) Biochemistry 30, 1761-17671. In the present studies, we have investigated the biosynthesis, processing, and glycosylation of the a-receptor and compared its structural and functional characteristics to those of the beta-receptor. Unlike an anti-peptide antibody, AbP2 (amino acid residues 964-979), to the human beta-receptor which detects a phosphorylation-specific conformation of the receptor, an antibody, AbP-alpha-2 (amino acid residues 956-971), to the corresponding region of the human alpha-receptor failed to do so. However, our studies revealed that the stability of the alpha-receptor is comparable to that of the beta-receptor. In addition, N-linked glycosylation of the alpha-receptor, like that of the beta-receptor, is not important in kinase activation. We have exploited the lack of an effect of N-linked oligosaccharides on the functioning of the alpha-receptor to develop a simple and rapid method for direct demonstration of ligand-induced noncovalently linked alpha-beta-receptor heterodimer formation. This method is based on the interaction between functionally active short and the long forms of two receptor types which can be resolved by denaturing gel electrophoresis.