RESUMEN
Sets of complementary lipidated coiled-coil forming peptides that fuse membrane fusion have been designed. The influence of the coiled-coil motif on the rate of liposome fusion was studied, by varying the number of heptad repeats. We found that an increased coiled-coil stability of complementary peptides translates into increased rates of membrane fusion of liposomes.
Asunto(s)
Lipopéptidos/química , Liposomas/química , Fusión de Membrana , Oligopéptidos/química , Dicroismo Circular , Fosfatidiletanolaminas/química , Polietilenglicoles/química , Proteínas SNARERESUMEN
Membrane fusion has an overarching influence on living organisms. The fusion of sperm and egg membranes initiates the life of a sexually reproducing organism. Intracellular membrane fusion facilitates molecular trafficking within every cell of the organism during its entire lifetime, and virus-cell membrane fusion may signal the end of the organism's life. Considering its importance, surprisingly little is known about the molecular-level mechanism of membrane fusion. Due to the complexity of a living cell, observations often leave room for ambiguity in interpretation. Therefore artificial model systems composed of only a few components are being used to further our understanding of controlled fusion processes. In this critical review we first give an overview of the hypothesized mechanism of membrane fusion and the techniques that are used to investigate it, and then present a selection of non-targeted and targeted model systems, finishing with current applications and predictions on future developments (85 references).
Asunto(s)
Membrana Dobles de Lípidos/química , Fusión de Membrana , Proteínas SNARE/química , Liposomas/química , Modelos Moleculares , NanotecnologíaRESUMEN
Inspired by the ubiquitous functions fulfilled by native proteins, the self-assembly of peptide amphiphiles (PAs) holds much promise for the creation of functional nanostructures. Typically, PAs are constructed by conjugating blocks of very different character: a hydrophilic peptide segment with a hydrophobic element (an alkyl chain, lipid, polymer or polypeptide). The resulting amphiphilicity governs the self-assembly process in aqueous solutions. This self-assembly process is guided by attractive forces (for example hydrophobic interactions, hydrogen bonding, electrostatic attraction) and repulsive forces (for example electrostatic repulsion, mechanical forces). The balance between these forces is responsible for the secondary structure of the peptide segment, and furthermore the size and shape of the assemblies that are formed. A result of PA self-assembly is that the properties of the peptide segment can be altered, as it is a general observation that peptides are more likely to exhibit a well-defined secondary structure at an interface (e.g. the corona of a micelle) than they are in solution. This characteristic of peptides can be exploited to give nanostructures with well-defined properties. The art of controlled PA self-assembly consists of carefully combining all the inter- and intramolecular forces to arrive at a material which is both structurally well-defined and has controllable functionalities. In this tutorial review the forces that act within PA nanostructures are discussed, that is, the effect of the hydrophobic block and peptide secondary structure on each other as well as on the aggregate as a whole. At the end of the review, a short section is devoted to the applications of these PA nanostructures.
Asunto(s)
Lípidos/química , Nanoestructuras/química , Fragmentos de Péptidos/química , Polímeros/química , Animales , HumanosRESUMEN
Until now, most preparative methods used to form polymeric vesicles involve either organic cosolvents or sonication. In this communication, we demonstrate for the first time a detergent-aided method to produce polymersomes. Peptidic polymersomes were formed from the rod-rod block copolymer PBLG(36)-E, where PBLG is hydrophobic poly(gamma-benzyl l-glutamate) and E is a hydrophilic designed peptide. The block copolymer was first solubilized by detergent micelles in aqueous buffer, after which the concentration of detergent was reduced by dilution, transforming the particle morphology in solution from mixed micelles to polymersomes. The polymersome formation was monitored with dynamic light scattering and confirmed with transmission electron microscopy. Polymersomes with average diameters of approximately 300 nm were obtained as well as discs with average diameters of approximately 100 nm. This detergent-based method can be used to create polymersomes with a range of properties, as verified by its application to another biocompatible block copolymer, the flexible polybutadiene(46)-b-poly(ethylene glycol)(30). The technique will be particularly useful when delicate biomacromolecules such as (membrane) proteins, peptides, or nucleic acids are to be encapsulated in the polymersomes because the detergents used are compatible with these compounds, and the possible denaturing effect of sonication or organic solvents on the biological activity of the molecule of interest is avoided.
Asunto(s)
Detergentes/química , Fragmentos de Péptidos/química , Polietilenglicoles/química , Ácido Poliglutámico/análogos & derivados , Polímeros/química , Agua/química , Micelas , Modelos Moleculares , Ácido Poliglutámico/química , SolucionesRESUMEN
A new class of peptide has been created, polypeptide-b-designed peptides, which unites the useful qualities of the two constituent peptide types. We demonstrate the synthesis and self-assembly possibilities of this class of peptide chimera with a series of amphiphilic polypeptide-b-designed peptides in which the hydrophobic block is poly(gamma-benzyl l-glutamate) (PBLG) and the hydrophilic block is a coiled-coil forming peptide (denoted E). The synthetic approach was to synthesize the coiled-coil forming peptide on the solid phase, followed by the ring-opening polymerization of gamma-benzyl l-glutamate N-carboxyanhydride, initiated from the N-terminal amine of the peptide E on the solid support. The polypeptide-b-peptide was then cleaved from the resin, requiring no further purification. Peptide E contains 22 amino acids, while the average length of the PBLG block ranged from 36 to 250 residues. This new class of peptide was applied to create a modular system, which relied on juxtaposing the properties of the component peptide types, namely the broad size range and structure-inducing characteristics of the polypeptide PBLG blocks, and the complex functionality of the sequence-designed peptide. Specifically, the different PBLG block lengths could be connected noncovalently with various hydrophilic blocks via the specific coiled-coil folding of E with K or K-poly(ethylene glycol), where K is a peptide of complementary amino acid sequence to E. In this way, nanostructures could be formed in water at neutral pH over the entire compositional range, which has not been demonstrated previously with such large PBLG blocks. It was found that the size, morphology (polymersomes or bicelles), and surface functionality could be specified by combining the appropriate modular building blocks. The self-assembled structures were characterized by dynamic light scattering, circular dichroism, scanning electron microscopy, cryogenic-transmission electron microscopy, fluorescence spectroscopy, and zeta-potential measurements. Finally, as the structures are able to encapsulate water-soluble compounds, and the surfaces are easily functionalized via the coiled-coil binding, it is expected that these peptide-based nanocapsules will be able to act as delivery vehicles to specific targets in the body.
Asunto(s)
Péptidos/síntesis química , Ácido Poliglutámico/análogos & derivados , Interacciones Hidrofóbicas e Hidrofílicas , Microscopía Electrónica de Transmisión , Resonancia Magnética Nuclear Biomolecular , Tamaño de la Partícula , Péptidos/química , Ácido Poliglutámico/química , Soluciones , Agua/químicaRESUMEN
The formation of a noncovalent triblock copolymer based on a coiled-coil peptide motif is demonstrated in solution. A specific peptide pair (E and K) able to assemble into heterocoiled coils was chosen as the middle block of the polymer and conjugated to poly(ethylene glycol) (PEG) and polystyrene (PS) as the outer blocks. Mixing equimolar amounts of the polymer-peptide block copolymers PS-E and K-PEG resulted in the formation of coiled-coil complexes between the peptides and subsequently in the formation of the amphiphilic triblock copolymer PS-E/K-PEG. Aqueous self-assembly of the separate peptides (E and K), the block copolymers (PS-E and K-PEG), and equimolar mixtures thereof was studied by circular dichroism, dynamic light scattering, and cryogenic transmission electron microscopy. It was found that the noncovalent PS-E/K-PEG copolymer assembled into rodlike micelles, while in all other cases, spherical micelles were observed. Temperature-dependent studies revealed the reversible nature of the coiled-coil complex and the influence of this on the morphology of the aggregate. A possible mechanism for these transitions based on the interfacial free energy and the free energy of the hydrophobic blocks is discussed. The self-assembly of the polymer-peptide conjugates is compared to that of polystyrene-b-poly(ethylene glycol), emphasizing the importance of the coiled-coil peptide block in determining micellar structure and dynamic behavior.