The Magainins: sequence factors relevant to increased antimicrobial activity and decreased hemolytic activity

The Magainins, two antimicrobial peptides found in the skin of the frog Xenopus laevis, and 50 Magainin analogs were synthesized by the method of simultaneous multiple peptide synthesis (SMPS). This series of peptides was prepared in order to examine the effects of omitting individual amino acids on antimicrobial activity. The series consisted of 22 Magainin 1 omission analogs having a C-terminal carboxyl (M1-C) and 23 Magainin 2 omission analogs having a C-terminal amide (M2-A), as well as both the C-terminal amide and carboxyl forms of Magainin 1 and Magainin 2. These peptides were tested against E. coli (Gram negative), S. epidermis (Gram positive) and C. albicans (yeast). Amino acid omissions in the N-terminal region (residues 1-14) resulted in the complete loss of antimicrobial activity in both Magainin series. These analogs also had very low hemolytic activity against human erythrocytes. However, analogs with omissions in the C-terminal region, especially residues alanine-15, glycine-18 or glutamic acid-19, while having equal or increased antimicrobial activity relative to the original Magainin 1 or Magainin 2 forms, had variable hemolytic action. Thus, both Magainin 1 and Magainin 2 with the glutamic acid 19 omission had equal activity against E. coli and increased activity against S. epidermis, while having lower hemolytic activity than the original sequences. The amide form of Magainin 2 with glycine 18 omitted had equal antimicrobial activity, but significantly increased hemolytic activity. The C-terminal carboxyl form of Magainin 1, however, showed equal antimicrobial activity, but substantially decreased hemolytic action.(ABSTRACT TRUNCATED AT 250 WORDS)