Interaction of Human Defensins With Escherichia Coli. Mechanism of Bactericidal Activity

J Clin Invest. 1989 Aug;84(2):553-61. doi: 10.1172/JCI114198.

Abstract

Defensins are small, cysteine-rich antimicrobial peptides that are abundant in human, rabbit, and guinea pig neutrophils (PMN). Three defensins (human neutrophil peptide defensin [HNP]-1, HNP-2, and HNP-3) constitute between 30 and 50% of the total protein in azurophil granules of human PMN. We examined the mechanism of HNP-mediated bactericidal activity against Escherichia coli ML-35 (i-, y-, z+) and its pBR322-transformed derivative, E. coli ML-35p. Under conditions that supported bactericidal activity, HNP-1 sequentially permeabilized the outer membrane (OM) and inner membrane (IM) of E. coli. Coincident with these events, bacterial synthesis of DNA, RNA, and protein ceased and the colony count fell. Although these events were closely coupled under standard assay conditions, OM permeabilization was partially dissociated from IM permeabilization when experiments were performed with E. coli that had been plasmolyzed by mannitol. Under such conditions, the rate and extent of bacterial death more closely paralled loss of IM integrity than OM permeabilization. Electron microscopy of E. coli that had been killed by defensins revealed the presence of striking electron-dense deposits in the periplasmic space and affixed to the OM. Overall, these studies show that HNP-mediated bactericidal activity against E. coli ML-35 is associated with sequential permeabilization of the OM and IM, and that inner membrane permeabilization appears to be the lethal event.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Blood Bactericidal Activity*
  • Blood Proteins / pharmacology*
  • Cathepsin G
  • Cathepsins / pharmacology
  • Cell Membrane Permeability / drug effects
  • Escherichia coli / drug effects*
  • Escherichia coli / metabolism
  • Escherichia coli / ultrastructure
  • Humans
  • Neutrophils / physiology*
  • Nucleic Acids / biosynthesis
  • Protein Biosynthesis
  • Serine Endopeptidases
  • alpha-Defensins*

Substances

  • Blood Proteins
  • Nucleic Acids
  • alpha-Defensins
  • human neutrophil peptide 1
  • Cathepsins
  • Serine Endopeptidases
  • CTSG protein, human
  • Cathepsin G