Antimicrobial activity of a C-terminal peptide from human extracellular superoxide dismutase

In this study, we show that RQA21 (RQAREHSERKKRRRESECKAA), a cationic and hydrophilic heparin-binding peptide corresponding to the C-terminal region of extracellular superoxide dismutase (SOD), exerts antimicrobial activity against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus subtilis and Candida albicans. The peptide was also found to induce membrane leakage of negatively charged liposomes. However, its antibacterial effects were abrogated in physiological salt conditions as well as in plasma.The results provide further evidence that heparin-binding peptide regions are multifunctional, but also illustrate that cationicity alone is not sufficient for AMP function at physiological conditions. However, our observation, apart from providing a link between heparin-binding peptides and AMPs, raises the hypothesis that proteolytically generated C-terminal SOD-derived peptides could interact with, and possibly counteract bacteria. Further studies are therefore merited to study a possible role of SOD in host defence.Antimicrobial peptides (AMP) are short cationic peptides widely distributed at biological surfaces prone to infection, playing important roles in innate immunity [1]. At present at least 900 different AMP have been discovered http://www.bbcm.univ.trieste.it/~tossi/search.htm webcite. Many AMPs are characterized by an amphipathic structure, where clusters of hydrophobic and cationic amino acids are spatially organized in sectors within the molecules. For example, AMPs comprise linear peptides, many of which may adopt α-helical and amphipathic conformation upon bacterial binding, peptides forming cysteine-linked antiparallel β-sheets, as well as cysteine-constrained loop structures. AMPs may also, however, be found among peptides not displaying such ordered structures as long as these are characterized by an over-representation of certain amino acids [1]. Considering the role of peptide secondary structure and amphphilicity, as well as