Role of immunoglobulin-like domains 2-4 of the platelet-derived growth factor alpha-receptor in ligand-receptor complex assembly.
Platelet-derived growth factor (PDGF) is a dimeric protein that exerts its effects through tyrosine kinase alpha- and beta-receptors. The extracellular part of each receptor is composed of five Ig-like domains. Recombinant forms of alpha-receptor domains 1-4 (alphaRD1-4), 1-3 (alphaRD1-3), and 1 and 2 (alphaRD1-2) were prepared after expression in Chinese hamster ovary cells and were used to study the assembly of soluble ligand-receptor complexes. When incubated with micromolar concentrations of PDGF, both alphaRD1-3 and alphaRD1-4 formed complexes of 1:2 molar composition, i.e. one dimeric PDGF molecule bound two soluble receptors. alphaRD1-3, in contrast to alphaRD1-4, formed detectable 1:1 complexes under conditions of ligand excess. alphaRD1-4 displayed an increased ability to form 1:2 complexes as compared with alphaRD1-3 under conditions of limiting concentrations of ligand. We thus conclude that Ig-like domain 4-mediated receptor-receptor interactions contribute to 1:2 PDGF.alphaRD1-4 complex formation. Since alphaRD1-4 and alphaRD1-3 were equipotent in blocking binding of subnanomolar concentrations of PDGF to cell-surface receptors, we also conclude that this effect is predominantly achieved through formation of Ig-like domain 4-independent 1:1 ligand-receptor complexes. Finally, since alphaRD1-2 bound PDGF-BB with high affinity, whereas PDGF-AA was bound only with low affinity, we conclude that Ig-like domain 3 of the PDGF alpha-receptor contains epitopes of particular importance for PDGF-AA binding and that most of the PDGF-BB-binding epitopes reside in Ig-like domains 1 and 2.
Miyazawa
K
K
Ludwig Institute for Cancer Research, S-751 24 Uppsala, Sweden.
Bäckström
G
G
Leppänen
O
O
Persson
C
C
Wernstedt
C
C
Hellman
U
U
Heldin
C H
CH
Ostman
A
A
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D007136:Immunoglobulins / Q000302:isolation & purification / Q000378:metabolism*; D009500:Neutralization Tests; D010982:Platelet-Derived Growth Factor / Q000378:metabolism; D011485:Protein Binding; D020796:Receptor, Platelet-Derived Growth Factor alpha; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism
D007136:Immunoglobulins; D010982:Platelet-Derived Growth Factor; D011994:Recombinant Proteins; D020796:Receptor, Platelet-Derived Growth Factor alpha; D017479:Receptors, Platelet-Derived Growth Factor