THE EGF RECEPTOR-BINDING OF RECOMBINANT HEREGULIN-BETA-1 EGF HYBRIDS IS BLOCKED BY HEREGULIN RESIDUE GLUTAMATE-195/

Defined sequences from the EGF-like domain of human heregulin-beta 1 ( HRG beta 1) were recombined with a synthetic gene fro human epidermal growth factor (hEGF) in an attempt to locate receptor-specific determi nants within the HRG beta 1 molecule that blocks its inappropriate ass ociation with the EGF receptor (EGFR). Receptor competition assays det ected only minor changes in relative EGFR affinity for those hybrids c ontaining up to 12 N-temimal HRG beta 1 residues. However, extending t he N-terminal substitution to include to 20 HRG beta residues resulted in a 100-fold drop in relative EGFR binding. Both interruption of the major beta-sheet structure of hEGF by insertion of a three amino acid loop present in HRG beta 1 and replacement of nearly the entire C-ter minal hEGF subdomain w;ith segments of HRG beta 1 sequence resulted in a 5-fold decreased EGFR affinity. The results presented here demonstr ate that while a substantial protein of the hEGF and HRG beta 1 protei n sequences were nearly interchangeable with regard to EGFR binding, t he introduction of HRG beta 1 residue Glu195 effected a major decrease in EGFR binding. (C) 1996 Academic Press.