Species right across the evolutionary scale from insects to mammals use peptides as part of their host-defense system to counter microbial infection. The primary structures of a large number of these host-defense peptides have been determined. While there is no primary structure homology, the peptides are characterized by a preponderance of cationic and hydrophobic amino acids. The secondary structures of many of the host-defense peptides have been determined by a variety of techniques. The acyclic peptides tend to adopt helical conformation, especially in media of low dielectric constant, whereas peptides with more than one disulfide bridge adopt beta-structures. Detailed investigations have indicated that a majority of these host-defense peptides exert their action by permeabilizing microbial membranes. In this review, we discuss structural and charge requirements for the interaction of endogenous antimicrobial peptides and short peptides that have been derived from them, with membranes.

Indolicidin, a 13-residue antimicrobial peptide isolated from cytoplasmic granules of bovine neutrophils, exhibits activity against Gram-positive and Gram-negative bacteria as well as fungi. Although indolicidin is bactericidal and permeabilizes the bacterial membranes, it does not lyse the bacterial cells. We examined the effect of bactericidal concentrations of indolicidin on the morphology of Escherichia coli cells and found that it induces filamentation. Further investigations showed that indolicidin inhibits DNA synthesis in E. coli cells at concentrations at which RNA and protein synthesis are either partially affected or not affected at all. Since inhibition of DNA synthesis is also known to induce filamentation in E. coli, it appears to contribute to the antimicrobial activity of indolicidin.

ities comparable to that of IL whereas ILF exhibits only poAbstract The antimicrobial and hemolytic activities of the 13-tent antimicrobial activity without any hemolytic activity. room temperature. The peptides were checked for purity on HPLC using a reverse-phase column (Bio Rad C4 Hi-Pore RP 304, 250 ×4.6 Key words: Indolicidin; Antimicrobial activity; Hemolytic mm), using a solvent system of 0.1% aqueous TFA and acetonitrile. activity; Membrane permeabilization All the peptides were > 90% pure. However, HPLC purified peptides were used for all studies. The peptides were characterized by amino acid and sequence analyses on a LKB 4151 Alpha plus analyser and 473A Applied Biosystems gas phase sequencer, respectively.

Melittin, the 26-residue predominant toxic peptide from bee venom, exhibits potent antibacterial activity in addition to its hemolytic activity. The synthetic peptide of 15 residues corresponding to its C-terminal end (MCF), which encompasses its most amphiphilic segment, is now being shown to possess antibacterial activity about 5^7 times less compared to that of melittin. MCF, however, is 300 times less hemolytic. An analog of MCF, MCFA, in which two cationic residues have been transpositioned to the N-terminal region from the C-terminal region, exhibits antibacterial activity comparable to that of melittin, but is only marginally more hemolytic than MCF. The biophysical properties of the peptides, like folding and aggregation, correlate well with their biological properties.z 1999 Federation of European Biochemical Societies.

Four broad-spectrum, 11 and 12 residue, novel antimicrobial peptides have been isolated from the adrenalinestimulated skin secretions of the Indian frog Rana tigerina. Sequences of these peptides have been determined by automated Edman degradation, by mass spectral analysis and confirmed by chemical synthesis. These peptides, which we have named as tigerinins, are characterized by an intramolecular disulfide bridge between two cysteine residues forming a nonapeptide ring. This feature is not found in other amphibian peptides. Conformational analysis indicate that the peptides tend to form ␤-turn structures. The peptides are cationic and exert their activity by permeabilizing bacterial membranes. Tigerinins represent the smallest, nonhelical, cationic antimicrobial peptides from amphibians.Antimicrobial peptides constitute a very important component of the innate immune system in organisms across the evolutionary scale (1-8). Amphibians being the first group of organisms forming a connecting link between land and water are forced to adopt and survive in a variety of conditions laden with pathogenic microbes. Thereby, they are endowed with an excellent chemical defense system composed of pharmacological and antimicrobial peptides (9). Bombinins were the first antimicrobial peptides characterized from the skin of Bombina variegata in 1969 (10). The discovery of magainins from the skin secretions of Xenopus laevis in 1987 (11) triggered extensive search and characterization of antimicrobial peptides from amphibians (12)(13)(14). Antimicrobial peptides from genus Rana share an interesting structural motif composed of a disulfidebridged cationic heptapeptide segment at the COOH-terminal end. Peptides with this motif include brevinins and esculentins which are composed of 24 and 46 amino acids, respectively (14). The primary structures of large number of peptides belonging to this family have been determined. Another group of short peptides composed of 13 residues called temporins, which do not contain this COOH-terminal ring, have also been characterized from frogs of genus Rana (15). However, considering the large variety of amphibian species in nature, antimicrobial peptides from only a small number of them have been characterized, that too only with respect to primary structure. Also, studies directed toward determining structure-function relationships have been confined to magainins (16) and dermaseptins (17, 18). Hence, characterizing host-defense peptides from other species would be of interest and could conceivably result in the identification of new structural motifs which would be useful in designing peptides for therapeutic applications. Rana tigerina is the predominant species of frogs found in India (19). The skin of these frogs have been used traditionally by some tribal communities to heal both open and burn wounds and the antimicrobial components could possibly contribute to the wound healing process (20). In this study, we have described the isolation and characterization of antimicrobial peptides from...