Human epidermal growth factor. Distinct roles of tyrosine 37 and arginine 41 in receptor binding as determined by site-directed mutagenesis and nuclear magnetic resonance spectroscopy.

ABSTRACT

Site-directed mutagenesis was employed to examine the function of two highly conserved residues, Tyr-37 and Arg-41, of human EGF (hEGF) in receptor binding. Both a conservative change to phenylalanine and a semi-conservative change to histidine at position 37 yield proteins with receptor affinity similar to wild-type hEGF. A non-conservative change to alanine results in a molecule with about 40% of the receptor affinity, indicating that an aromatic residue is not essential at this position. Both conservative (to lysine) and non-conservative (to alanine) substitutions at position 41 drastically reduced receptor binding to less than 0.5% of the wild-type activity. 1D-NMR data indicate that the replacement of Arg-41 by lysine does not significantly alter the native protein conformation. Thus, Arg-41 may be directly involved in ligand receptor interaction, whereas the side chain of Tyr-37, although possibly important structurally, is not essential for receptor binding.