SummaryDuring the last years, the importance of antibacterial peptides has attracted considerable attention. We report here that peptides derived from the fifth domain of beta-2 glycoprotein I (b2GPI), a human heparin binding plasma protein, have antibacterial activities against Gram-positive and Gram-negative bacteria. Streptococcus pyogenes, an important human pathogen that can survive and grow in human blood, has developed mechanisms to escape the attack by these peptides. Thus, protein H and M1 protein, two surface proteins of the highly pathogenic S. pyogenes AP1 strain, bind full-length b2GPI and thereby prevent the processing of b2GPI by proteases from polymorphonuclear neutrophils (PMNs) into antibacterial peptides. In addition, protein H and M1 protein, released from the bacterial cell wall by PMN-derived proteases, bind to, and inhibit the activity of, b2GPI-derived antibacterial peptides. Taken together, the data suggest that the interaction between the streptococcal proteins and b2GPI or b2GPI-derived peptides presents a novel mechanism to resist an antibacterial attack by b2GPI-cleavage products.
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