Widespread resistance to antibiotics in current clinical use is increasing at an alarming rate. Novel approaches in antimicrobial therapy will be required in the near future to maintain control of infectious diseases. An enormous array of small cationic peptides exists in nature as part of the innate defense systems of organisms ranging from bacteria to humans. For most linear peptides, such as magainins and cecropins, a common feature is their capacity to form an amphipathic alpha-helix (with polar and nonpolar groups on opposite faces of the helix), a structural feature believed to be important in their antimicrobial function as membrane-lytic agents. A massive effort over the past ten years has resulted in a better understanding of the molecular mechanism of these antimicrobial peptides and the production of more potent analogues. To date, however, few of these peptides appear to have clinical potential, especially for systemic use, due to insufficient selectivity between target and host cells. Recently we developed a new strategy in the design of antimicrobial peptides. These linear cationic peptides, which form amphipathic beta-sheets rather than alpha-helices, demonstrated superior selectivity in binding to the lipids contained in bacterial vs. mammalian plasma membranes. We propose here to extend the investigation of this new class of peptides by studying smaller compounds of similar design to: 1) define the minimum peptide length necessary for antimicrobial activity; 2) probe the sequence dependence for maximal activity and selectivity by using strategic tryptophan, alanine and glycine substitutions; 3) explore the mode of action and compare the molecular mechanism to that of other antimicrobial peptides; 4) measure peptide activity and stability under physiological conditions; and 5) test for cytotoxicity on normal and transformed human cells. This project should result in the design of smaller and more selective antimicrobial peptides that produces leads for animal and clinical testing. As the arsenal of available antibiotics dwindles due to ever-increasing resistance of bacteria to the drugs in clinical use, these linear beta-sheet-forming antimicrobial peptides provide a new avenue worthy of further exploration.
