The role of Gram-negative envelope LPS on the bactericidal properties of proteins and peptides: the case of eosinophil cationic protein

摘要

The human Eosinophil Cationic Protein (ECP) is an antimicrobial protein involved in host defense. The protein presents a high affinity to lipopolysaccharides (LPS) and can specifically agglutinate Gram-negative bacteria cells. We have identified the ECP antimicrobial domain that can reproduce most of the protein activity, and partly retain the cell aggregation properties. With the aim to reduce the antibacterial predicted region we have synthesized a peptide only containing the two α-helices of the antimicrobial domain linked by and aminohexanoic acid. To better understand the ECP antimicrobial mechanism of action and evaluate the contribution of the LPS components, we have assayed a battery of E. coli K12 strain variants that present distinct chemotypes (Ra to Re chemotypes), which are defective in some of the genes involved in the LPS synthesis and display progressively truncated LPS at their outer membrane. The data correlates the LPS structure with the bacteria viability and reveals that both the length and charge of the LPS alters the bacteria cell susceptibility to the protein cytotoxicity.