1,721,121 research outputs found
Alpha-helical antimicrobial peptides-Using a sequence template to guide structure-activity relationship studies
No full textAn important class of cytolytic antimicrobial peptides (AMPs) assumes an amphipathic, alpha-helical conformation that permits efficient interaction with biological membranes. Host defence peptides of this type are widespread in nature, and numerous synthetic model AMPs have been derived from these or designed de novo based on their characteristics. In this review we provide an overview of the 'sequence template' approach which we have used to design potent artificial helical AMPs, to guide structure-activity relationship studies aimed at their optimization, and to help identify novel natural AMP sequences. Combining this approach with the rational use of natural and non-proteinogenic amino acid building blocks has allowed us to probe the individual effects on the peptides' activity of structural and physico-chemical parameters such as the size, propensity for helical structuring, amphipathic hydrophobicity, cationicity, and hydrophobic or polar sector characteristics. These studies furthermore provided useful insights into alternative modes of action for natural membrane-active helical peptides
Photoinduced interaction of Ru(bpy)32+ with nucleotides and nucleic acids in the presence of S2O82-: a transient conductivity study
No full textThe photochemical reactions of Ru(bpy)32+ with single- and double-stranded DNA, polynucleotides and purine-containing nucleotides in argon-saturated aqueous solution in the presence of S2O82- were studied using time-resolved absorption and conductivity methods. The conversion of Ru(bpy)33+ to Ru(bpy)32+, monitored spectroscopically either after rapid mixing with substrate or after laser flash excitation (λ(exc) = 353 nm) is quantitative at nucleotide-to-sensitizer ratios [N]/[S] of 1-2 for DNA and other guanine-containing compounds. Conductivity measurements following the laser pulse revealed a fast conductivity increase (rise time, less than 0.1 ms) due to the formation of protons and, to a lesser degree, to charged species of much lower ion mobility. A slower component in the 0.01-1 s range was observed for nucleic acids; its amplitude is markedly reduced at pH 6-9. In buffered neutral solution the signal is replaced by a slight decrease in conductivity. Electronically excited Ru(bpy)32+ bound to DNA reacts with S2O82- to form Ru(bpy)33+ and SO4.- as primary oxidizing species both of which react with bases. The resulting base radicals react subsequently with Ru(bpy)33+ and Ru(bpy)32+ or the ligands in the ruthenium complex, producing protons which give rise to the slower conductivity increase. The formation of single-strand breaks and the ensuing release of condensed counterions does not appear to contribute significantly to the slow component. The transient conductivity behaviour is sensitive to the single- or double-stranded nature of DNA
Molecular diversity in gene-encoded, cationic antimicrobial polypeptides.
No full textGene-encoded, ribosomally synthesised antimicrobial peptides (AMPs) are an ancient and pervasive component of the innate defence mechanisms used by multicellular organisms to control the natural flora and combat pathogens. Bacteria also produce such AMPs to maintain ecological niches free of rival strains. Several hundred different peptides have been characterised to date, and they show a marked degree of variability in both sequence and structure, having evolved to act against distinct microbial targets in different physiological contexts. Many of these peptides appear to function via a selective, but not receptor-mediated, permeabilisation of microbial membranes, while others interact with specific membrane associated or intracellular targets. This review presents a broad survey of different AMP structural classes, emphasising both their molecular diversity and underlying similarities. The mode of action of these peptides and potential for biomedical and other application is also briefly discussed
Design and Engineering Strategies for Synthetic Antimicrobial Peptides
No full textThousands of antimicrobial peptides (AMPs) of prokaryotic, fungal, plant, or animal origin have been identified, and their potential as lead compounds for the design of novel therapeutic agents in the treatment of infection, for stimulating the immune system, or in countering septic shock has been widely recognized. Added to this is their possible use in prophylaxis of infectious diseases for animal or plant protection, for disinfection of surgical instruments or industrial surfaces, and for food preservation among other commercially important applications. Since the early eighties, AMPs have been subject to a vast number of studies aimed at understanding what determines their potency and spectrum of activities against bacterial or fungal pathogens, and at maximizing these while limiting cytotoxic activities toward host cells. Much research has also been directed toward understanding specific mechanisms of action underlying the antimicrobial activity and selectivity, to be able to redesign the peptides for optimal performance. A central theme in the mode of action of many AMPs is their dynamic interaction with biological membranes, which involves various properties of these peptides such as, among others, surface hydrophobicity and polarity, charge, structure, and induced conformational variations. These features are often intimately interconnected so that engineering peptides to independently adjust any one property in particular is not an easy task. However, solid-phase peptide synthesis allows the use of a large repertoire of nonproteinogenic amino acids that can be used in the rational design of peptides to finely tune structural and physicochemical properties and precisely probe structure–function relationships
A study of some ruthenium polypyridyl complexes as DNA binders and photocleavage reagents
No full textThe nature of the binding of several ruthenium polypyridyl complexes containing 2, 2`-bipyridine (bipy), 4, 4`-dimethyl-2, 2`-bipyridine (DMB), 1,10-phenanthroline (phen), 4,7-diphenyl-1,10-phenanthroline(DPP), 2, 2`, 2`-terpyridine (terpy), 2, 2`-biquinoline (biq), 1,4,5,8-tetraazaphen-anthrene (TAP) and 1,4,5,8,9,12-hexaazatriphenylene (HAT), with calf thymus DNA, poly[d(A-T)] and poly[d(G-C)] were studied by absorption and emission spectroscopy, DNA melting techniques, and emission lifetime measurements. In low ionic strength phosphate buffer, spectroscopic changes and DNA stabilization depended on the polypyridyl ligands present, and indicated binding that varied from substantially electrostatic to intercalative. Ru(bipy)2(HAT)2+ and Ru(phen)32+, which bind by partial intercalation, also show a strong preference for poly[d(A-T)]. The emission quantum yields for most complexes were increased in the presence of DNA. An exception was Ru(TAP)32+ which has a markedly reduced emission quantum yield and lifetime in the presence of poly[d(G-C)] or CT-DNA, due to photoredox interaction with guanines. Emission decays of the complexes generally showed multiexponential behaviour. The ability of the ruthenium complexes to sensitise DNA cleavage was determined using pBR322 plasmid DNA. Ru(TAP)32+ is the most efficient sensitiser while uncharged complexes and complexes with very short-lived excited states do not cleave DNA
Amphipathic, alpha-helical antimicrobial peptides.
No full textGene-encoded antimicrobial peptides are an important component of host defense in animals ranging from insects to mammals. They do not target specific molecular receptors on the microbial surface, but rather assume amphipathic structures that allow them to interact directly with microbial membranes, which they can rapidly permeabilize. They are thus perceived to be one promising solution to the growing problem of microbial resistance to conventional antibiotics. A particularly abundant and widespread class of antimicrobial peptides are those with amphipathic, α-helical domains. Due to their relatively small size and synthetic accessibility, these peptides have been extensively studied and have generated a substantial amount of structure-activity relationship (SAR) data. In this review, α-helical antimicrobial peptides are considered from the point of view of six interrelated structural and physicochemical parameters that modulate their activity and specificity: sequence, size, structuring, charge, amphipathicity, and hydrophobicity. It begins by providing an overview of how these vary in peptides from different natural sources. It then analyzes how they relate to the currently accepted model for the mode of action of α-helical peptides, and discusses what the numerous SAR studies that have been carried out on these compounds and their analogues can tell us. A comparative analysis of the many α-helical, antimicrobial peptide sequences that are now available then provides further information on how these parameters are distributed and interrelated. Finally, the systematic variation of parameters in short model peptides is used to throw light on their role in antimicrobial potency and specificity. The review concludes with some considerations on the potentials and limitations for the development of α-helical, antimicrobial peptides as antiinfective agents
Amphipathic alpha helical antimicrobial peptides: A systematic study of the effects of structural and physical properties on biological activity.
No full textAntimicrobial peptides (AMPs) that assume an amphipathic α helical structure are widespread in nature. Their activity depends on several parameters including the sequence, size, degree of structure formation, cationicity, hydrophobicity and amphipathicity. The analysis of numerous natural AMPs provided representative values for these parameters and led to a sequence template with which to generate potent artificial lead AMPs. Sequences were then varied in a rational manner, using both natural and nonproteinogenic amino acids, to probe the individual roles of each parameter in modulating biological activity. A high cationicity combined with a stabilized amphipathic α helical structure conferred enhanced cidal activity towards all the cell types considered, and was a requirement for Gram-positive bacteria and fungi. An elevated helicity also correlated with increased hemolytic activity. The structural requirements for activity against several Gram-negative bacteria were instead considerably less stringent, so that it persisted in peptides in which formation of a helical structure and/or amphipathicity were impeded. Either a reduced charge or a reduced hydrophobicity resulted in generally inactive peptides. These observations, combined with the kinetics of bacterial membrane permeabilization and time-killing are discussed in terms of currently accepted models of action for this type of peptide. The simple guidelines obtained in this study allowed the design of highly active shortened AMPs and may be generally useful in the development of this type of peptides as anti-infective agents
Design of synthetic antimicrobial peptides based on sequence analogy and amphipathicity
No full textNovel α-helical antimicrobial peptides have been devised by comparing the N-terminal sequences of many of these peptides from insect, frog and mammalian families, extracting common features, and creating sequence templates with which to design active peptides. Determination of the most frequent amino acids in the first 20 positions for over 80 different natural sequences allowed the design of one peptide, while a further three were based on the comparison of the sequences of α-helical antimicrobial peptides derived from the mammalian cathelicidin family of precursors. These peptides were predicted to assume a highly amphipathic α-helical conformation, as indicated by high mean hydrophobic moments. In fact, circular dichroism experiments showed clear transitions from random coli in aqueous solution to an α-helical conformation on addition of trifluoroethanol. All four peptides displayed a potent antibacterial activity against: selected gram-positive and gram-negative bacteria (minimum inhibitory concentrations in the range 1-8 μM), including some antibiotic resistant strains. Permeabilization of both the outer and cytoplasmic membranes of the gram-negative bacterium, Escherichia coli, by selected peptides was quite rapid and a dramatic drop in colony forming units was observed within 5 min in time-killing experiments. Permeabitization of the cytoplasmic membrane of the gram-positive bacterium, Staphylococcus aureus, was instead initially quite slow, gathering speed after 45 min, which corresponds to the time required for significant inactivation in time-killing studies. The cytotoxic activity of the peptides, determined on several normal and transformed cell lines, was generally low at values within the minimum inhibitory concentration range
- …
