University of California , Department of Medicine , San Francisco .
Trans Assoc Am Physicians 101 : 24-32 ( 1988)
Abstract
The effect of ligand binding on PDGF receptor conformation was examined using peptide antisera directed against specific receptor domains .
Antiserum 83 , which recognizes the receptor 's carboxyl terminus , preferentially immunoprecipitated the ligand-activated form of the PDGF receptor from 35S-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 receptor was induced by the three different forms of PDGF ( AA and BB homodimers and AB heterodimer ) 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 AMP-PNP , a nonhydrolyzable analog of ATP .
The functional significance of receptor conformation was examined in CHO 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 .
Ligand-induced receptor autophosphorylation was reduced but present in cells expressing receptors that lacked a major site of autophosphorylation and was present in cells expressing receptors that lacked the kinase insert domain.(ABSTRACT TRUNCATED AT 250 WORDS )