BACTERICIDAL ACTIVITY OF SYNTHETIC PEPTIDES BASED ON THE STRUCTURE OFTHE 55-KILODALTON BACTERICIDAL PROTEIN FROM HUMAN NEUTROPHILS

Short (10- to 11-mer) hydrophilic peptides based on the structure of t he 55-kDa bactericidal protein (BP55, B/PI, and CAP57) from human neut rophil granules were identified from the hydropathy plot of the 456-am ino-acid sequence predicted from the nucleotide sequences of cDNA clon es for BP55 and B/PI. Peptides corresponding to amino acid residues 90 to 99 (peptide #90-99), 86 to 99, or 90 to 102 of BP55 were bacterici dal toward 5 x 10(6) Pseudomonas aeruginosa cells at 0.6 x 10(-5) to 1 .5 x 10(-5) M and killed an Escherichia coli rough strain at 3 x 10(-5 ) M. The #90-99 peptide with a cysteine added at the amino terminus (C #90-99) was approximately 10 times more active than #90-99, killing P. aeruginosa at 1.5 x 10(-6) M. Peptides representing amino acid residu es 27 to 37, 118 to 127, and 160 to 170 and the first 10 amino acids o f the signal sequence for BP55 were not bactericidal. When coupled to either keyhole limpet hemocyanin or ovalbumin protein carriers through the thiol group, the C#90-99 peptide was not diminished on a molar ba sis in its capacity for killing of P. aeruginosa. Two other relatively hydrophilic peptides with an added amino-terminal cysteine, peptides C#227-236 and C#418-427, were not bactericidal at 1.2 x 10(-4) M or at 100 times the effective bactericidal concentration of C#90-99. The C# 90-99 peptide killed E. coli at 1.5 x 10(-5) M, or at 10 times the con centration required to kill an equal number of P. aeruginosa cells. Al though Pseudomonas cepacia and Staphylococcus aureus were resistent to killing by the parent BP55 molecule, they were susceptible to the C#9 0-99 and #90-99 peptides in the same concentration range as was E. col i. When all peptides were compared for the ability to neutralize E. co li O55:B5 endotoxin in a Limulus amoebocyte lysate assay, the C#227-23 6, C#418-427, and #160-170 peptides completely inhibited gelation at a 10(-4) M concentration. All other synthetic peptides, including bacte ricidal peptide #90-99 and its congeners, lacked endotoxin-neutralizin g activity at the highest concentration tested (4.5 x 10(-4) M). A hyb rid of the C#227-236 and #90-99 peptides (CHybrid) was identical to th e C#227-236 peptide component in effectiveness for carrying out endoto xin neutralization and was fivefold better than the #90-99 peptide in its capacity for killing P. aeruginosa.