The focus of infection is surrounded by epithelial cells that express b -defensins

1. The focus of infection is surrounded by epithelial cells that express b-defensins Courtesy of Lide Liu (Univ. of California, Los Angeles)

2. Antimicrobial Peptides • Antimicrobial peptides are evolutionarily ancient weapons. Their widespread distribution and abundance (> 800 eukaryotic peptides described) throughout the animal and plant kingdoms suggests that antimicrobial peptides have served a fundamental role in the successful evolution of complex multicellular organisms. • The fundamental structural principle underlying all classes is the ability of the molecule to adopt a shape in which clusters of hydrophobic and cationic amino acids are spatially organized in discrete sectors of the molecule ('amphipathic' design). • All antimicrobial peptides are derived from larger precursors, including a signal sequence. Post-translational modifications include proteolytic processing, and in some cases glycosylation, carboxy-terminal amidation and amino-acid isomerization and halogenation. • Some peptides are derived by proteolysis from larger proteins, such as buforin II from histone 2A and lactoferricin from lactoferrin. • Most multicellular organisms express a cocktail comprising multiple peptides from several of these structural classes within their 'defensive' tissues.

3. Antimicrobial peptides from plants and invertebrates Schroder-CMLS-99

4. Mammalian Defensins Yang et al, Trends Immunol, 02

5. In human, Paneth Cells in Crypts of Leiberkuhn secrete a-defensins or cryptins.proHD5 is proteolytically cleaved extrcellularly by trypsin. It also highlights that this enzyme has other nondigestive function.Unmodified proHD5 also has antimicrobial activity, especially when tested against Gram-positive L. monocytogenes.The differential antibacterial activity between the HD5 forms that exist in vivo suggests that proteolytic processing could be a mechanism that diversifies the spectrum of antibiotic activity from a single antimicrobial gene product.

6. Basis of Specificity of Antimicrobial Peptides

7. The Shai–Matsuzaki–Huang (SMH) model for AMP activity

8. How do antimicrobial peptides actually kill microbes? • The creation of physical holes that cause cellular contents to leak out [BioPhys. J. 79, 2002 (2000)]. • Fatal depolarization of the normally energized bacterial membrane [PNAS 86, 6597 (1989)]. • The activation of deadly processes, such as autolysis, by the induction of hydrolases that degrade the cell wall [Arch. Microbiol. 141, 249 (1985)]. • The scrambling of the usual distribution of lipids between the leaflets of the bilayer, resulting in disturbance of membrane functions [BBA 1462, 1 (1999)]. • The damaging of critical intracellular targets after internalization of the peptide. For example, the peptide pyrrhocoricin, inhibits ATPase actions of DnaK and prevent chaperone-assisted protein folding [Biochem. 40, 3016 (2001)].

9. Cathelicidins • Processed by neutrophil elastase in the extracellular milieu. • Extracellular proteolytic activation of AMPs is also conserved in lower vertebrates and insects. • Antimicrobial activity is synergistic with lysozyme and lactoferrin, PNAS95(1988),9541 • Activity is dependent on the concentration of NaCl (activity diminishes 4- to 5-fold as the total concentration of NaCl is elevated from 60 to 155 mM), PNAS95(1988),9541.

10. Mouse Cathelicidin, CRAMP, Protects the Skin from Group A Streptococcus Nizet et al, Nature 2001

11. Important cytokines secreted by macrophages in response to bacterial products