Optimizing Human Epidermal Growth Factor for its Endurance and Specificity Via Directed Evolution: Functional Importance of Leucine at Position 8

Epidermal growth factor regulates cell proliferation and migration by binding and activating the extracellular region of its receptor. Many engineered EGFs with enhanced agonist activity are produced, yet the short half-life and poor environmental tolerance of EGF limits its physiological application. By using a more stable porcine EGF as the template in the staggered extension process, two mutants of human and porcine EGF, hL8P and pP8L, were obtained with improved targeting towards normal cells. The comparative studies of hEGF and mutants were conducted to evaluate their activities as agonists. The mutants showed specificity for the proliferation and migration of normal and cancer cells, i.e. both pP8L and hL8P promoted the proliferation and migration of normal cells while delayed that of cancer cells. Both mutants preserved the structure thermostability of hEGF and pP8L showed improved acidic tolerance than hEGF. For the metabolism analysis in HEK293T cells, hL8P and pP8L demonstrated the lower rate of both mutants-EGFR internalization and biodegradation, but higher recycling to the cell surface. This study not only enhanced EGF agonist activity without loss of endurance but also provided a new application foreground for trauma therapy and cancer targeting therapy.