ChBac3.4: A novel proline-rich antimicrobial peptide from goat leukocytes

We isolated a new proline-rich peptide, ChBac3.4, from leukocytes of the goat (Capra hirca) and determined its amino acid sequence by Edman degradation and mass spectrometry. ChBac3.4 (RFRLPFRRPPIRIHPPPFYPPFRRFL-NH2) had over 50% sequence identity to the Bac5 peptides found in the leukocytes of goats, sheep and cattle. ChBac3.4 exhibited broadspectrum antimicrobial activity, especially under low salt conditions. Since E. coli ML35p treated with ChBac3.4 manifested increased outer and inner membrane permeability and a rapid and extensive loss of cytoplasmic potassium, the antimicrobial properties of this peptide may depend, in part, on its ability to damage microbial membranes. Nevertheless, even high concentrations of ChBac3.4 were not significantly hemolytic for human erythrocytes. In vitro, ChBac3.4 was selectively cytotoxic, damaging human K562 erythroleukemia cells and human U937 hystiocytic lymphoma cells, but not other human target cells. ChBac3.4 appears to differ from other proline-rich cathelicidins in virtue of its increased ability to damage microbial membranes. This novel antimicrobial peptide warrants further study, especially with respect to its various effects on microbial and mammalian cells.