Antimicrobial peptides are an important component of the natural defense against invading pathogens. They are distributed in most living organisms and have been demonstrated to kill bacteria, fungi, virus and even transformed or cancerous cells. They are potent candidates for new antibiotics. Cathelicidin Pc-CATH1 is a cathelicidin-derived myeloid antimicrobial peptide identified from Phasianus colchicus with strong antimicrobial activity against most of bacteria and fungi tested, including the clinically isolated (IS) drug-resistant strains. Considering the uniform distribution of net positive charge in both C- and N-terminus sequence of cathelicidin Pc-CATH1 and most of hydrophobic amino acid residues (aa) positioned in middle of the sequence, the antimicrobial peptide was used to investigate the structure-function relationship by truncating gradually N- or C-terminus amino acid residue. More than 10 modified peptide homologues (20-26 aa length) of cathelicidin Pc-CATH1 were found to keep strong antimicrobial abilities. The possible relationships between bioactivities including antimicrobial and hemolytic abilities, components of secondary structure, hydrophobicity, amphipathicity, net charge, and sequence length were investigated. The current work provided suggestions for structural and functional modification of linear, α-helical antimicrobial peptides containing no disulfided bridges. DEFB18 and DEFB20 are found in the human β-defensin gene cluster by using a computational genomic search strategy. To investigate their biological functions, we constructed expression vectors in E.coli and got purified peptides by HPLC. DEFB18 and DEFB20 were found to contain ABTS radical scavenging ability, but they could not kill microorganisms including Escherichia coli, Staphylococcus aureus, Bacillus subtilis, and Candida albicans.
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