Structure, membrane orientation, mechanism, and function of pexiganan — A highly potent antimicrobial peptide designed from magainin

The growing problem of bacterial resistance to conventional antibiotic compounds and the need for new antibiotics have stimulated interest in the development of antimicrobial peptides (AMPs) as human therapeutics. Development of topically applied agents, such as pexiganan (also known as MSI-78, an analog of the naturally occurring magainin2, extracted from the skin of the African frog Xenopus laevis) has been the focus of pharmaceutical development largely because of the relative safety of topical therapy and the uncertainty surrounding the long-term toxicology of any new class of drug administered systemically. The main hurdle that has hindered the development of antimicrobial peptides is that many of the naturally occurring peptides (such as magainin), although active in vitro, are effective in animal models of infection only at very high doses, often close to the toxic doses of the peptide, reflecting an unacceptable margin of safety. Though MSI-78 did not pass the FDA approval, it is still the best-studied AMP to date for therapeutic purposes. Biophysical studies have shown that this peptide is unstructured in solution, forms an antiparallel dimer of amphipathic helices upon binding to the membrane, and disrupts membrane via toroidal-type pore formation. This article covers functional, biophysical, biochemical and structural studies on pexiganan.