University of California , Department of Medicine , San Francisco .
J Biol Chem 263 : 12805-8 ( 1988)
Abstract
The effect of ligand binding on platelet-derived growth factor ( PDGF ) receptor conformation was examined using peptide antibodies directed against specific receptor domains .
Antiserum 83 , which was directed to the receptor 's carboxyl terminus ( residues 934-951 ) , preferentially immunoprecipitated the ligand-activated form of the PDGF receptor from S-labeled BALB/c 3T3 cells .
By contrast , two antisera directed against other receptor sequences precipitated unactivated and activated receptors equally well .
Denatured receptors were recognized equally by all antisera , even 83 .
Thus , ligand activation caused a change in PDGF receptor conformation that enhanced accessibility of the antibody to the carboxyl terminus .
The activated receptor conformation was induced by three different forms of PDGF ( AA and BB homodimers and AB heterodimers ) and was reversed by suramin , a polyanionic compound that dissociates PDGF from the receptor .
The inhibitory effect of suramin on receptor conformation was abolished by the phosphatase inhibitor , sodium orthovanadate , suggesting that receptor phosphorylation mediated the conformational change .
In a cell-free assay , the change in receptor conformation was induced by PDGF only in the presence of ATP and was inhibited by adenyl-5'-yl imidodiphosphate , a nonhydrolyzable analog of ATP .
The functional significance of receptor conformation was examined in Chinese hamster ovary fibroblasts transfected with wild-type or mutated forms of the PDGF receptor .
When receptor tyrosine kinase activity was abolished by a mutation of the ATP binding site the receptor no longer underwent PDGF-induced conformational change and did not mediate PDGF-induced mitogenesis even though 125I-PDGF binding was normal .
These findings show that ligand binding elicits a phosphorylation-dependent change in PDGF receptor conformation that may be important for receptor function .