MUTATIONS WITHIN SUBDOMAIN-II OF THE EXTRACELLULAR REGION OF EPIDERMAL GROWTH-FACTOR RECEPTOR SELECTIVELY ALTER TGF-ALPHA BINDING

The interactions of epidermal growth factor (EGF) and transforming gro wth factor alpha (TGF alpha) with the epidermal growth factor receptor (EGFR) were examined by insertion mutagenesis of the receptor. Sevent een insertions were made throughout a construct containing only the ex tracellular domain, This truncated receptor (sEGFR) was secreted and h ad a dissociation constant similar to that of the full-length solubili zed receptor. Receptors with insertions within subdomain III were not secreted, Two receptors with insertions at positions 291 and 474, whic h border subdomain III, have significantly decreased binding to both E GF and TGF alpha relative to wild type, This confirms previous work de monstrating that subdomain III forms the primary binding site for EGF and TGF alpha. Four of the mutants within subdomain II had a decreased binding to TGF alpha relative to wild type, but had wild type binding to EGF. These results suggest that a region within subdomain II may s electively regulate the binding of TGF alpha. Two receptors which cont ained insertions within subdomains II and IV, approximately equidistan t from the center of subdomain III, bound twofold more ligand molecule s than wild type receptor, with an affinity similar to that of wild ty pe receptor. These findings suggest that insertion at these positions allows the access of more than one ligand molecule to the binding site . (C) 1995 Academic Press, Inc.