scholarly journals Androctonin, a hydrophilic disulphide-bridged non-haemolytic anti-microbial peptide: a plausible mode of action

2000 ◽  
Vol 345 (3) ◽  
pp. 653-664 ◽  
Author(s):  
Charles HETRU ◽  
Lucienne LETELLIER ◽  
Ziv OREN ◽  
Jules A. HOFFMANN ◽  
Yechiel SHAI
Keyword(s):  
Mode Of Action ◽  
Cell Envelope ◽  
Acyl Chain ◽  
Lipid Vesicles ◽  
Attenuated Total Reflection ◽  
Haemolytic Activity ◽  
Bacterial Membranes ◽  
Slow Kinetics ◽  
High Concentrations ◽  
Lytic Peptides

Androctonin is a 25-residue non-haemolytic anti-microbial peptide isolated from the scorpion Androctonus australis and contains two disulphide bridges. Androctonin is different from known native anti-microbial peptides, being a relatively hydrophilic and non-amphipathic molecule. This raises the possibility that the target of androctonin might not be the bacterial membrane, shown to be a target for most amphipathic lytic peptides. To shed light on its mode of action on bacteria and its non-haemolytic activity, we synthesized androctonin, its fluorescent derivatives and its all-D-amino acid enantiomer. The enantiomer preserved high activity, suggesting a lipid-peptide interaction between androctonin and bacterial membranes. In Gram-positive and (at higher concentrations) Gram-negative bacteria, androctonin induced an immediate perturbation of the permeability properties of the cytoplasmic membrane of the bacterial energetic state, concomitant with perturbation of the morphology of the cell envelope as revealed by electron microscopy. Androctonin binds only to negatively charged lipid vesicles and induces the leakage of markers at high concentrations and with a slow kinetics, in contrast with amphipathic α-helical anti-microbial peptides that bind and permeate negatively charged vesicles, and to a smaller extent also zwitterionic ones. This might explain the selective lytic activity of androctonin towards bacteria but not red blood cells. Polarized attenuated total reflection-Fourier transform infrared spectroscopy revealed that androctonin adopts a β-sheet structure in membranes and did not affect the lipid acyl chain order, which supports a detergent-like effect. The small size of androctonin, its hydrophilic character and its physicochemical properties are favourable features for its potential application as a replacement for commercially available antibiotics to which bacteria have developed resistance.

scholarly journals Structure and organization of the human antimicrobial peptide LL-37 in phospholipid membranes: relevance to the molecular basis for its non-cell-selective activity

1999 ◽  
Vol 341 (3) ◽  
pp. 501-513 ◽  
Author(s):  
Ziv OREN ◽  
Jeffrey C. LERMAN ◽  
Gudmundur H. GUDMUNDSSON ◽  
Birgitta AGERBERTH ◽  
Yechiel SHAI
Keyword(s):  
Antimicrobial Peptide ◽  
Mode Of Action ◽  
Lipid Membranes ◽  
Antimicrobial Agents ◽  
Eukaryotic Cells ◽  
Haemolytic Activity ◽  
Human Immune System ◽  
Bacterial Membranes ◽  
Proteolytic Resistance ◽  
Charged Membranes

The antimicrobial peptide LL-37 belongs to the cathelicidin family and is the first amphipathic α-helical peptide isolated from human. LL-37 is considered to play an important role in the first line of defence against local infection and systemic invasion of pathogens at sites of inflammation and wounds. Understanding its mode of action may assist in the development of antimicrobial agents mimicking those of the human immune system. In vitrostudies revealed that LL-37 is cytotoxic to both bacterial and normal eukaryotic cells. To gain insight into the mechanism of its non-cell-selective cytotoxicity, we synthesized and structurally and functionally characterized LL-37, its N-terminal truncated form FF-33, and their fluorescent derivatives (which retained structure and activity). The results showed several differences, between LL-37 and other native antimicrobial peptides, that may shed light on its in vivoactivities. Most interestingly, LL-37 exists in equilibrium between monomers and oligomers in solution at very low concentrations. Also, it is significantly resistant to proteolytic degradation in solution, and when bound to both zwitterionic (mimicking mammalian membranes) and negatively charged membranes (mimicking bacterial membranes). The results also showed a role for the N-terminus in proteolytic resistance and haemolytic activity, but not in antimicrobial activity. The LL-37 mode of action with negatively charged membranes suggests a detergent-like effect via a ‘carpet-like’ mechanism. However, the ability of LL-37 to oligomerize in zwitterionic membranes might suggest the formation of a transmembrane pore in normal eukaryotic cells. To examine this possibility we used polarized attenuated total reflectance Fourier-transform infrared spectroscopy and found that the peptide is predominantly α-helical and oriented nearly parallel with the surface of zwitterionic-lipid membranes. This result does not support the channel-forming hypothesis, but rather it supports the detergent-like effect.

Structural characteristics of tetanolysin and its binding to lipid vesicles

1982 ◽  
Vol 152 (2) ◽  
pp. 888-892
Author(s):  
S Rottem ◽  
R M Cole ◽  
W H Habig ◽  
M F Barile ◽  
M C Hardegree
Keyword(s):  
Structural Characteristics ◽  
Lipid Vesicles ◽  
Molar Ratio ◽  
Molar Ratios ◽  
High Concentrations

Tetanolysin binding to lipid vesicles was found to depend on the molar ratio of cholesterol to phospholipid, being low in vesicles containing up to 20 mol% cholesterol and high in vesicles containing more than 33 mol%. High concentrations of purified tetanolysin preparations formed arc- and ring-shaped structures. The structures were not readily detectable in diluted preparations unless incubated with lipid vesicles containing high molar ratios of cholesterol to phospholipid. It is suggested that the toxin is concentrated on the vesicles to local concentrations high enough to form the arcs and rings.

Interactions of the Antimicrobial Peptide Maculatin 1.1 and Analogues with Phospholipid Bilayers

2011 ◽  
Vol 64 (6) ◽  
pp. 798 ◽  
Author(s):  
David I. Fernandez ◽  
Marc-Antoine Sani ◽  
Frances Separovic
Keyword(s):  
Antimicrobial Peptide ◽  
Solid State Nmr ◽  
Acyl Chain ◽  
Head Group ◽  
Group Interactions ◽  
Bacterial Membranes ◽  
Helical Content ◽  
Lipid System ◽  
Acyl Chains ◽  
Mixed Bilayer

The interactions of the antimicrobial peptide, maculatin 1.1 (GLFGVLAKVAAHVVPAIAEHF-NH2) and two analogues, with model phospholipid membranes have been studied using solid-state NMR and circular dichroism spectroscopy. Maculatin 1.1 and the P15G and P15A analogues displayed minimal secondary structure in water, but with zwitterionic dimyristoylphosphatidylcholine (DMPC) vesicles displayed a significant increase in α-helical content. In mixed phospholipid vesicles of DMPC and anionic dimyristoylphosphatidylglycerol (DMPG), each peptide was highly structured with ~80% α-helical content. In DMPC vesicles, the native peptide displayed moderate head group interaction and significant perturbation of the lipid acyl chains. In DMPC/DMPG vesicles, maculatin 1.1 promoted formation of a DMPG-enriched phase and moderately increased disorder towards acyl chain ends of DMPC in the mixed bilayer. Both analogues showed reduced phospholipid head group interactions with DMPC but displayed significant interactions with the mixed lipid system. These effects support the preferential activity of these antimicrobial peptides for bacterial membranes.

Mechanism of Action of Progestins in the Treatment of Hormone-dependent Breast Cancer.

1975 ◽  
Vol 61 (6) ◽  
pp. 501-508 ◽  
Author(s):  
Francesco Di Carlo ◽  
Giovanni Pacilio ◽  
Giuseppe Conti
Keyword(s):  
Breast Cancer ◽  
Estrogen Receptors ◽  
Mechanism Of Action ◽  
Mode Of Action ◽  
Binding Capacity ◽  
Specific Receptors ◽  
High Concentrations ◽  
Good Agreement

The in vitro interference of some gestagens with the binding of 3H-17 β-oestradiol to cytosol specific receptors was investigated with a view to elucidating the mechanism of action of progestins in the treatment of human hormone-dependent breast cancer. A decrease (up to 85 %) of oestradiol binding capacity was observed with high concentrations of progesterone, clogestone and medrogestone. These findings are in good agreement with those previously obtained by the same progestins in our laboratory on rat uterine estrogen receptors in vitro or in vivo. These results provide support for the hypothesis that the mode of action of progestins in the therapy of mammary and perhaps uterine carcinomas is to some extent related to the inhibition of oestradiol binding to cytosol specific receptors.

scholarly journals Mode of Action of the Antimicrobial Peptide Aureocin A53 from Staphylococcus aureus

2002 ◽  
Vol 68 (11) ◽  
pp. 5274-5280 ◽  
Author(s):  
Daili Jacqueline Aguilar Netz ◽  
Maria do Carmo de Freire Bastos ◽  
Hans-Georg Sahl
Keyword(s):  
Mode Of Action ◽  
Neutral Lipids ◽  
Membrane Damage ◽  
Model Membranes ◽  
Bacterial Cells ◽  
Gram Staining ◽  
Rapid Release ◽  
High Concentrations ◽  
Staphylococcus Simulans ◽  
Tryptophan Emission

ABSTRACT We investigated the mode of action of aureocin A53 on living bacterial cells and model membranes. Aureocin A53 acted bactericidally against Staphylococcus simulans 22, with >90% of the cells killed within a few minutes. Cell death was followed by lysis, as indicated by a clearing of the cell suspension and Gram staining. Aureocin A53 rapidly dissipated the membrane potential and simultaneously stopped biosynthesis of DNA, polysaccharides, and protein. Aureocin A53 induced a rapid release of preaccumulated glutamate and Rb+. Experiments on model membranes demonstrated that aureocin A53 provoked significant leakage of carboxyfluorescein (CF) exclusively from acidic liposomes but only at relatively high concentrations (0.5 to 8 mol%). Thus, the bactericidal activity of aureocin A53 derives from membrane permeation via generalized membrane destruction rather than by formation of discrete pores within membranes. Tryptophan emission fluorescence spectroscopy demonstrated interaction of aureocin A53 with both acidic and neutral membranes, as indicated by similar blue shifts. Since there was no significant aureocin A53-induced CF leakage from neutral liposomes, its appears that the peptide does interact with neutral lipids without provoking membrane damage.

Molecular Simulations of Gram-Negative Bacterial Membranes Come of Age

2020 ◽  
Vol 71 (1) ◽  
pp. 171-188
Author(s):  
Wonpil Im ◽  
Syma Khalid
Keyword(s):  
Recent Progress ◽  
Cell Envelope ◽  
Molecular Simulations ◽  
Molecular Architecture ◽  
Future Directions ◽  
Gram Negative ◽  
Bacterial Membranes ◽  
Antibiotic Development ◽  
Multiple Cell ◽  
Made In

Gram-negative bacteria are protected by a multicompartmental molecular architecture known as the cell envelope that contains two membranes and a thin cell wall. As the cell envelope controls influx and efflux of molecular species, in recent years both experimental and computational studies of such architectures have seen a resurgence due to the implications for antibiotic development. In this article we review recent progress in molecular simulations of bacterial membranes. We show that enormous progress has been made in terms of the lipidic and protein compositions of bacterial systems. The simulations have moved away from the traditional setup of one protein surrounded by a large patch of the same lipid type toward a more bio-logically representative viewpoint. Simulations with multiple cell envelope components are also emerging. We review some of the key method developments that have facilitated recent progress, discuss some current limitations, and offer a perspective on future directions.

scholarly journals Slow kinetics of inositol 1,4,5-trisphosphate-induced Ca2+ release: is the release ‘quantal’ or ‘non-quantal’?

1997 ◽  
Vol 323 (1) ◽  
pp. 123-130 ◽  
Author(s):  
Ludwig MISSIAEN ◽  
Humbert DE SMEDT ◽  
Jan B. PARYS ◽  
Ilse SIENAERT ◽  
Henk SIPMA ◽  
...  
Keyword(s):  
Low Dose ◽  
Slow Phase ◽  
Quantal Response ◽  
Published Evidence ◽  
A7r5 Cells ◽  
Slow Kinetics ◽  
Inositol 1,4,5 Trisphosphate ◽  
Long Time ◽  
High Concentrations ◽  
Kinetics Of

Inositol 1,4,5-trisphosphate (InsP3)-induced Ca2+ release from intracellular stores is generally assumed to be a ‘quantal’ process because low InsP3 concentrations mobilize less Ca2+ than high concentrations and a submaximal concentration does not release all the InsP3-mobilizable Ca2+. However, some recent reports questioned the generally accepted view that a low dose of InsP3 is unable to empty the whole store. We have now challenged the stores of permeabilized A7r5 cells in InsP3 for much longer periods than previously reported, to assess directly whether the slow phase of the release would empty the whole store (a non-quantal response) or only a fraction of it (a quantal response). Addition of a maximal [InsP3] at the end of a prolonged (92 min) stimulation with a submaximal [InsP3] resulted in additional Ca2+ release. Experiments in which the stores were challenged with different submaximal InsP3 concentrations for long time periods revealed that a lower [InsP3] never released the same amount of Ca2+ as a higher [InsP3]. This quantal pattern of Ca2+ release occurred both at 25 °C and at 4 °C. There was a time-dependent increase in the fraction of Ca2+ recruited by the lower compared with the higher [InsP3]. This recruitment of Ca2+ persisted if the [InsP3] was decreased, but was largely prevented by palmitoyl-CoA, a potent blocker of the luminal Ca2+ translocation between individual store units. ATP, in the presence of InsP3, released Ca2+ under conditions permitting the recruitment of no additional InsP3 receptors, indicating that an all-or-none emptying of a fraction of the stores cannot be the only mechanism responsible for quantal Ca2+ release in A7r5 cells. We conclude that some of the previously published evidence for a non-quantal Ca2+ release pattern should be reinterpreted.

scholarly journals The effect of flavomycin on the synthesis and transfer of lipid-linked saccharides in pig brain

1982 ◽  
Vol 201 (3) ◽  
pp. 481-487 ◽  
Author(s):  
Ernst Bause ◽  
Günter Legler
Keyword(s):  
Mode Of Action ◽  
Direct Interaction ◽  
Inhibitory Effects ◽  
Dolichyl Phosphate ◽  
Pig Brain ◽  
Endogenous Protein ◽  
High Concentrations ◽  
Sugar Derivatives ◽  
Competitive Nature ◽  
Derivatives Of

Particulate membrane fractions from pig brain catalyse the synthesis of lipid-linked sugar derivatives of the dolichyl phosphate pathway. Flavomycin, a phosphoglycolipid antibiotic produced by various species of streptomycetes, interferes with the formation of these glycolipids to a different extent. The formation of dolichyl phosphate glucose was shown to be most susceptible to the antibiotic, being blocked by about 50% in the presence of 0.2mm-flavomycin, whereas the synthesis of dolichyl diphosphate N-acetylglucosamine, dolichyl diphosphate chitobiose and dolichyl diphosphate chitobiosyl mannose required higher concentrations to achieve a comparable inhibition. Although the formation of dolichyl phosphate mannose was hardly affected, the accumulation of oligosaccharides with five to seven sugar units was observed, when dolichyl diphosphate oligosaccharides were synthesized with GDP-[14C]mannose in the presence of 1mm-flavomycin. This indicates that the inhibition of the synthesis of larger-sized oligosaccharides, known to be mediated by lipid-bound mannose, was not caused by an actual deficiency in dolichyl phosphate mannose. At flavomycin concentrations that inhibited the formation of dolichyl phosphate glucose by 50%, the transfer of lipid-linked saccharides to either the hexapeptide Tyr-Asn-Gly-Thr-Ser-Val or endogenous protein acceptors was hardly influenced. The mode of action of flavomycin is still obscure, but seems not to be of a competitive nature, since the inhibition was unaffected by increasing concentrations of dolichyl phosphate. Some evidence indicates that, besides a direct interaction of the antibiotic with some transferases, a non-specific incorporation into the membrane and alteration of its properties might be responsible for those inhibitory effects on all enzymes which were observed at high concentrations of flavomycin.

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