A SMALL V-SIS PLATELET-DERIVED GROWTH-FACTOR (PDGF) B-PROTEIN DOMAIN IN WHICH SUBTLE CONFORMATIONAL-CHANGES ABROGATE PDGF RECEPTOR INTERACTION AND TRANSFORMING ACTIVITY

Deletion scanning mutagenesis within the transforming region of the v-sis oncogene was used to dissect structure-function relationships. Mutations affecting codons within a domain encoding amino acids 136 through 148 had no effect upon homodimer formation or recognition by antisera which detect determinants dependent upon native intrachain disulfide linkages, yet the same mutations completely abolished transforming activity. A platelet-derived growth factor B (PDGF B) monoclonal antibody that prevents its interaction with PDGF receptors recognized v-sis, Δ142 (deletion of codon 142), and Δ148 but not Δ136, Δ137, or Δ139 mutants. These findings mapped the epitope recognized by this monoclonal antibody to include amino acid residues 136 to 139. Furthermore, mutations in the codon 136 to 148 domain caused markedly impaired ability to induce PDGF receptor tyrosine phosphorylation. Thus, subtle conformational alterations in this small domain critically affect PDGF receptor recongition and/or functional activation.