Protein Engineering vol.9 no.9 pp.781-788, 1996 The functional importance of Leul5 of human epidermal growth factor in receptor binding and activation

'To whom correspondence should be addressed The biological importance of Leu 15 of epidermal growth factor (EGF) is suggested by its conservation through evolution, its critical location in the domain-domain inter-face of EGF and its close proximity to Arg41, a residue that is crucial for receptor binding and activation. Mutagen-esis of Leul5 of human EGF (hEGF) was employed to examine the role of this residue in the ligand-receptor interaction. The relative receptor affinities of the hEGF variants, as determined by radioreceptor competition assays, varied depending on the amino acid substitution. The L15F, L15W and L15V hEGF analogues had receptor affinities 45, 26 and 18 % respectively of wild type hEGF. The L15A and L15R analogues displayed receptor affinities of only 2.4 and 1.6 % relative to wild type hEGF. No bindin