Bactericidal activity of Lys49 and Asp49 myotoxic phospholipases A2 from Bothrops asper snake venom: Synthetic Lys49 myotoxin II‐(115−129)‐peptide identifies its bactericidal region

Abstract

Mammalian group‐II phospholipases A 2 (PLA 2) of inflammatory fluids display bactericidal properties, which are dependent on their enzymatic activity. This study shows that myotoxins II (Lys49) and III (Asp49), two group‐II PLA 2 isoforms from the venom of Bothrops asper, are lethal to a broad spectrum of bacteria. Since the catalytically inactive Lys49 myotoxin II isoform has similar bactericidal effects to its catalytically active Asp49 counterpart, a bactericidal mechanism that is independent of an intrinsic PLA 2 activity is demonstrated. Moreover, a synthetic 13‐residue peptide of myotoxin II, comprising residues 115−129 (common numbering system) near the C‐terminal loop, reproduced the bactericidal effect of the intact protein. Following exposure to the peptide or the protein, accelerated uptake of the hydrophobic probe N‐phenyl‐N‐naphthylamine was observed in susceptible but not in resistant bacteria, indicating that the lethal effect was initiated on the bacterial membrane. The outer membrane, isolated lipopolysaccharide (LPS), and lipid A of susceptible bacteria showed higher binding to the myotoxin II‐(115−129)‐peptide than the corresponding moieties of resistant strains. Bacterial LPS chimeras indicated that LPS is a relevant target for myotoxin II‐(115−129)‐peptide. When heterologous LPS of the resistant strain was present in the context of susceptible bacteria, the chimera became resistant, and vice versa. Myotoxin II represents a group‐II PLA 2 with a direct bactericidal effect that is independent of an intrinsic enzymatic activity, but adscribed to the presence of a short cluster of basic/hydrophobic amino acids near its C‐terminal loop.