Lipopolysaccharide binding and antibacterial activities of a synthetic peptide representing amino acids 90-101 of bactericidal/permeability-increasing protein.

The bactericidal/permeability-increasing protein (BPI) of polymorphonuclear leukocytes is a potent antibacterial agent specific for gram-negative bacteria. BPI can bind to lipopolysaccharide (LPS) and neutralize its toxicity. However, little is known about the specific site and mechanisms of the BPI involved in this LPS binding and antibacterial activities. This study compared the amino acid sequences among BPI, cecropin A, magainin 2, and polymyxin B, and identified a common structure among these four bactericidal agents. They share a basic amphipathic alpha helix motif (Baah). A short peptide that represents amino acids 90-101 of BPI was then synthesized to test if it possessed any LPS binding and antibacterial activities. Results from in vitro lymphocyte culture indicated this peptide was able to inhibit LPS-induced lymphocyte proliferation, suggesting that it may interact with LPS. This LPS binding ability of BPI peptide 90-101 was further supported by the results from HPLC assays which showed the mobility of the peptide shifted in the presence of LPS. Furthermore, the antibacterial spectra of this peptide and cecropin peptide 1-11 were very similar to that of polymyxin B, even though the antibacterial activities of these two peptides were less potent than that of polymyxin B. In addition, the antibacterial activities of these two peptides and polymyxin B were inhibited by free LPS or a high concentration of MgCl2. These results thus suggest that a common structure (Baah) and antibacterial mechanism may be involved in these antibacterial agents.