Abstract: Host defense peptides are part of innate immunity, often possessing the potential to kill both Gram-negative and Gram-positive microorganisms, rapidly and directly, and modulate other parts of host innate immunity. Today, more than 700 cationic peptides have been identified, originating from bacteria, fungi, insects, tunicates, amphibians, crustaceans, birds, fish and mammals, including humans. These peptides all have certain conserved physical features, including a net positive charge, approximately 50% hydrophobic amino acid content, and sizes that range from 12 to 50 amino acids; however, from these physical features, virtually any type of secondary structure can arise, including alpha-helix, beta-sheet and loop structures of beta-turn and extended loops. The multitude of cationic peptide sources, structures and spectra of activities is matched by a number of complex and controversial models that attempt to describe and explain the mode of action.
Little is known about the sequence requirements of short host defense peptides. With the help of our novel technique, using an artificially created, luminescence-producing Gram-negative bacterium and peptide synthesis on cellulose, we investigated the sequence requirements of these peptides. Hundreds of peptides were tested for their ability to kill Pseudomonas aeruginosa. Complete substitutional analysis of different indolicidin variants, as well as a semi-random peptide library with about 3000 members were studied. The complete substitutional analysis gave us information about the importance of each single position within a peptide sequence, whereas the peptide library provided broader information concerning the composition of amino acids, resulting in an active antimicrobial peptide. The data were analyzed using a quantitative structure-activity relationship approach (QSAR) to identify sequence patterns that discriminated among superior activity, equivalent activity and inactive peptide sequences. This information provides us with mechanistic cues to better understand the mode of action of the short antimicrobial peptides. The results of these measurements and analyses will be discussed in detail.

Brief Biography of the Speaker:
Kai Hilpert is a team leader of the research team "Bioactive Peptides" at the Karlsruhe Institute of Technology (KIT) in Germany. He is a member of the new “BioInterfaces” program, within the Helmholtz Association. He studied biochemistry at Humboldt University in Germany. Kai Hilpert had the opportunity to be a postdoctoral fellow with the Canadian Institutes of Health Research (CIHR) program at the University of British Columbia, Canada. For 15 years, he has used the peptide SPOT synthesis method to study various protein/protein or peptide/protein interactions. In the past 5 years, his research interests have focused on host defense peptides. Currently, he is investigating sequence requirements of short cationic host defense peptides with activity against Pseudomonas aeruginosa. He has authored or co-authored over 25 peer-reviewed scientific papers, which have been published in journals that include Nature Biotechnology, Nature Protocols and Chemistry & Biology. Further information can be found at www.kaihilpert.de.