Action Of Gramicidin Research Articles

Mechanism of membrane damage induced by the amphipathic peptides gramicidin S and melittin

The action of gramicidin S and melittin on human erythrocytes, Staphylococcus aureus and Escherichia coli was studied as an extension of the previous study (Katsu, T., Ninomiya, C., Kuroko, M., Kobayashi, H., Hirota, T. and Fujita, Y. (1988) Biochim. Biophys. Acta 939, 57–63). These amphipathic peptides stimulated the release of membrane phospholipids outside cells in a concentration range causing permeability change. The shape change of erythrocytes from normal discoid to spiculate form was observed just prior to the release of membrane components. We have proposed the following action mechanism of gramicidin S and melittin. The peptide molecules were predominantly accumulated in the outer half of the bilayer, deforming the erythrocyte cell into crenature. A large accumulation made the membrane structure unstable, resulting in the release of membrane fragments and the simultaneous enhancement of permeability. The action mechanism of these peptides was compared with that of simple surfactants.

Dication and trication which can increase the permeability of Escherichia coli outer membrane

Recent success in the preparation of the monomer, dimer and trimer in compound 48 80 prompted us to investigate the action of these compounds on Escherichia coli cells. It was found that compound 48 80 inhibited growth of E. coli cells, while the monomer, dimer and trimer in 48 80 did not. However, the following experiments showed that the dimer and trimer disrupted the permeability barrier of the outer membrane of E. coli. First, addition of the dimer or trimer in cell suspension stimulated the uptake of tetraphenylphosphonium cation. Second, the synergistic effect of the dimer on the action of gramicidin caused the efflux of K +. In experiments using isolated cytoplasmic membrane vesicles, addition of gramicidin alone caused the efflux of K +. Thus, it was speculated that, with whole cells, the dimer formed some defect structure in the outer membrane, through which gramicidin reached the cytoplasmic membrane and increased the K + permeability. The temperature dependence of efflux of K + showed that the dimer in 48 80 rendered the outer membrane permeable to gramicidin at temperatures above the phase transition of the outer membrane.

The peptide antibiotic gramicidin D A specific reactivator of tyrocidine-inhibited transcription

The sporulating bacterial strain Bacillus brevis (ATCC 8185) produces two types of peptide antibiotics, the linear gramicidins and the cyclic tyrocidines. Their effects on transcription in vitro were studied: 1. 1. RNA synthesis catalized by RNA polymerase and DNA as template, both from B. brevis cells, is inhibited by the addition of gramicidin maximally to 50% as compared to controls without gramicidin. This inhibition is dependent on the concentration of gramicidin as well as on that of RNA polymerase. 2. 2. Transcription of DNA is also inhibited by tyrocidine. This inhibition is partially compensated by the addition of gramicidin. Here, the action of gramicidin is again dependent on its concentration and on that of RNA polymerase. 3. 3. This counteraction of gramicidin occurs only with RNA polymerase from B. brevis. Enzyme preparations of other origin are additively inhibited by gramicidin when previously inhibited by tyrocidine. The specific action pattern of gramicidin and tyrocidine in connection with the B. brevis RNA polymerase supports the notion that the two peptide antibiotics may be involved in a gene regulatory mechanism during sporogenesis.

The gramicidin A transmembrane channel: characteristics of head-to-head dimerized (L,D) helices.

A series of helical structures for gramicidin A, with alternating L and D residues, are characterized as to number of residues per turn, atoms in hydrogenbonded rings, and dihedral angles. Because of alternating peptide C-O directions, these helices are capable of forming head-to-head hydrogen-bonded dimers with the capacity of functioning as transmembrane channels. The dimers are characterized as to channel length, pore size, and expected ion selectivity. In a test of the proposed head-to-head association for channel formation, the malonyl dimer [N,N'-(dideformyl gramicidin A)-malonamide] was synthesized. The chemical and conformational integrity of the product was verified by nuclear magnetic resonance; in lipid bilayer studies, the dimer was found to be a potent mediator of ion conductance with the predicted concentration dependence.Thus, the results on malonyl gramicidin A prove head-to-head association in formation of the transmembrane channel, and the results are consistent with the specific geometrical configuration involved in head-to-head dimerization of pi((L,D)) helices. At this stage, the action of gramicidin A on membranes with lipid-layer thicknesses of 30 A or less can best be understood in terms of the pi((L,D)) helix with 6.3 residues per turn.

Antibacterial activity of acyclic decapeptide analogs of gramicidin S.

Three acyclic decapeptide analogs of gramicidin S, although found to possess antibacterial activity, apparently have modes of action which differ from that of the naturally occurring cyclic antibiotic. In contrast to the immediate action of gramicidin S, one of the decapeptides produced complete bacteriostasis only after several cell divisions had occurred. Furthermore, mixtures of gramicidin S with either of two of the acyclic peptides were synergistic. Some implications of these findings are discussed.

The hemolytic action of gramicidin and tyrocidin.

Summary(1) The courses of hemolysis for gramicidin, tyrocidin, and mixtures of the two have been determined. Tyrocidin causes a rapid hemolysis, the extent being proportional to the concentration of the lysin. Gramicidin causes a slower initial rate of hemolysis but this initial lag is followed by rapid destruction of red blood cells at a rate at least equal to the initial rate due to tyrocidin. Mixtures of the two components gave hemolysis patterns characteristic of the proportions of gramicidin and tyrocidin. (2) An alcohol-soluble substance or substances present in the wall of the red blood cell of the rat, possibly phospholipid in nature, combines with tyrocidin, and to a lesser extent with gramicidin, causing them to lose their hemolytic activity.

Mode of Action of Gramicidin

Conclusions1. Gramicidin and tyrocidine depress the surface tension of aqueous solutions. Tyrocidine is more active in this regard than is gramicidin. 2. The ability of gramicidin to depress surface tension is improved by the addition of organic solvents such as glycerin which increases the solubility of gramicidin. 3. Serum decreases the activity of tyrocidine less than it does the activity of gramicidin, sodium oleate and aerosol OT. 4. The bactericidal and hemolytic effects of gramicidin are destroyed by heat but its property of altering surface tension is heat stable.