Structure and evolution of the Ivy protein family, unexpected lysozyme inhibitors in Gram-negative bacteria

Proc Natl Acad Sci U S A. 2007 Apr 10;104(15):6394-9. doi: 10.1073/pnas.0611019104. Epub 2007 Apr 3.


Part of an ancestral bactericidal system, vertebrate C-type lysozyme targets the peptidoglycan moiety of bacterial cell walls. We report the crystal structure of a protein inhibitor of C-type lysozyme, the Escherichia coli Ivy protein, alone and in complex with hen egg white lysozyme. Ivy exhibits a novel fold in which a protruding five-residue loop appears essential to its inhibitory effect. This feature guided the identification of Ivy orthologues in other Gram-negative bacteria. The structure of the evolutionary distant Pseudomonas aeruginosa Ivy orthologue was also determined in complex with hen egg white lysozyme, and its antilysozyme activity was confirmed. Ivy expression protects porous cell-wall E. coli mutants from the lytic effect of lysozyme, suggesting that it is a response against the permeabilizing effects of the innate vertebrate immune system. As such, Ivy acts as a virulence factor for a number of Gram-negative bacteria-infecting vertebrates.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carrier Proteins / chemistry*
  • Carrier Proteins / genetics*
  • Cluster Analysis
  • Crystallography
  • Escherichia coli Proteins / chemistry*
  • Escherichia coli Proteins / genetics*
  • Evolution, Molecular*
  • Models, Molecular*
  • Muramidase / antagonists & inhibitors*
  • Phylogeny*
  • Protein Conformation
  • Species Specificity


  • Carrier Proteins
  • Escherichia coli Proteins
  • Ivy protein, E coli
  • Muramidase