Substitution of lysine for arginine at position 42 of human transforming growth factor-alpha eliminates biological activity without changing internal disulfide bonds. |
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Authors: | D Defeo-Jones J Y Tai G A Vuocolo R J Wegrzyn T L Schofield M W Riemen and A Oliff |
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Institution: | Department of Cancer Research, Merck Sharp and Dohme Research Laboratories, West Point, Pennsylvania 19486. |
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Abstract: | Transforming growth factor-alpha (TGF-alpha) is a growth-promoting protein that binds to the epidermal growth factor (EGF) receptor. To identify critical residues that govern TGF-alpha-EGF receptor binding, we prepared site-specific substitution mutants of TGF-alpha. Mutant proteins were tested in receptor-binding and mitogenesis assays. Semiconservative substitutions at positions 4, 12, 18, and 45 decreased biological activity 2.1- to 14-fold. The conservative substitution of lysine for arginine at position 42 completely eliminated biological activity. Amino acid composition analysis of proteolytic fragments from TGF-alpha and the Lys-42 mutant indicated that these proteins contained the same disulfide bonds. These studies suggest that arginine 42 may be a contact point for TGF-alpha-EGF receptor interaction. |
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