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1.
Cell Mol Life Sci ; 2020 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-32025743

RESUMO

Misfolding and aggregation of proteins is strongly linked to several neurodegenerative diseases, but how such species bring about their cytotoxic actions remains poorly understood. Here we used specifically-designed optical reporter probes and live fluorescence imaging in primary hippocampal neurons to characterise the mechanism by which prefibrillar, oligomeric forms of the Alzheimer's-associated peptide, Aß42, exert their detrimental effects. We used a pH-sensitive reporter, Aß42-CypHer, to track Aß internalisation in real-time, demonstrating that oligomers are rapidly taken up into cells in a dynamin-dependent manner, and trafficked via the endo-lysosomal pathway resulting in accumulation in lysosomes. In contrast, a non-assembling variant of Aß42 (vAß42) assayed in the same way is not internalised. Tracking ovalbumin uptake into cells using CypHer or Alexa Fluor tags shows that preincubation with Aß42 disrupts protein uptake. Our results identify a potential mechanism by which amyloidogenic aggregates impair cellular function through disruption of the endosomal-lysosomal pathway.

2.
FEBS Lett ; 2019 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-31721178

RESUMO

The constituent paired helical filaments (PHFs) in neurofibrillary tangles are insoluble intracellular deposits central to the development of Alzheimer's disease (AD) and other tauopathies. Full-length tau requires the addition of anionic cofactors such as heparin to enhance assembly. We have shown that a fragment from the proteolytically stable core of the PHF, tau 297-391 known as 'dGAE', spontaneously forms cross-ß-containing PHFs and straight filaments under physiological conditions. Here, we have analysed and compared the structures of the filaments formed by dGAE in vitro with those deposited in the brains of individuals diagnosed with AD. We show that dGAE forms PHFs that share a macromolecular structure similar to those found in brain tissue. Thus, dGAEs may serve as a model system for studying core domain assembly and for screening for inhibitors of tau aggregation.

3.
Chem Sci ; 10(33): 7801-7806, 2019 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-31588329

RESUMO

Most low molecular weight gelators are chiral, with racemic mixtures often unable to form gels. Here, we show an example where all enantiomers, diastereomers and racemates of a single functionalized dipeptide can form gels. At high pH, different self-assembled aggregates are formed and these directly template the structures formed in the gel. Hence, solutions and gels with different properties can be accessed simply by varying the chirality. This opens up new design rules for the field.

4.
Dalton Trans ; 48(41): 15371-15375, 2019 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-31107476

RESUMO

The heterometallic Zn2Dy2 entity bearing partially saturated metal centres covalently decorates a highly ordered amyloid fibril core and the functionalised assembly exhibits catalytic Lewis acid behaviour.

5.
Biomolecules ; 9(2)2019 01 29.
Artigo em Inglês | MEDLINE | ID: mdl-30700058

RESUMO

Alzheimer's disease (AD) is the most common type of dementia and, after age, the greatest risk factor for developing AD is the allelic variation of apolipoprotein E (ApoE), with homozygote carriers of the ApoE4 allele having an up to 12-fold greater risk of developing AD than noncarriers. Apolipoprotein E exists as three isoforms that differ in only two amino acid sites, ApoE2 (Cys112/Cys158), ApoE3 (Cys112/Arg158), and ApoE4 (Arg112/Arg158). These amino acid substitutions are assumed to alter ApoE structure and function, and be responsible for the detrimental effects of ApoE4 via a mechanism that remains unclear. The hypothesis that a structural difference between ApoE4 and ApoE3 (and ApoE2) is the cause of the ApoE4-associated increased risk for AD forms the basis of a therapeutic approach to modulate ApoE4 structure, and we were therefore interested in screening to identify new chemical probes for ApoE4. In this regard, a high-yield protocol was developed for the expression and purification of recombinant full-length ApoE, and three diverse biophysical screening assays were established and characterized; an optical label-free assay (Corning Epic) for hit identification and microscale thermophoresis (MST) and isothermal titration calorimetry (ITC) as orthogonal assays for hit confirmation. The 707 compounds in the National Institute of Health clinical collection were screened for binding to ApoE4, from which six confirmed hits, as well as one analogue, were identified. Although the compounds did not differentiate between ApoE isoforms, these data nevertheless demonstrate the feasibility of using a biophysical approach to identifying compounds that bind to ApoE and that, with further optimization, might differentiate between isoforms to produce a molecule that selectively alters the function of ApoE4.


Assuntos
Apolipoproteínas E/química , Sondas Moleculares/análise , Apolipoproteínas E/isolamento & purificação , Apolipoproteínas E/metabolismo , Humanos , Sondas Moleculares/metabolismo , Estrutura Molecular , Isoformas de Proteínas
6.
Methods Mol Biol ; 1873: 109-122, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30341606

RESUMO

Many proteins and peptides are able to self-assemble in solution in vitro and in vivo to form amyloid-like fibrils. These fibrils share common structural characteristics. In order for a fibril to be characterized as amyloid, it is expected to fit certain criteria including the composition of cross-ß. Here we describe how the formation of amyloid fibrils can be characterized in vitro using a variety of methods including circular dichroism and intrinsic tyrosine/tryptophan fluoresence to follow conformational changes; Thioflavin and/or ThS assembly to monitor nucleation and growth; transmission electron microscopy to visualize fibrillar morphology and X-ray fiber diffraction to examine cross-ß structure.


Assuntos
Amiloide/química , Proteínas Amiloidogênicas/química , Modelos Moleculares , Conformação Proteica , Amiloide/metabolismo , Peptídeos beta-Amiloides/química , Peptídeos beta-Amiloides/metabolismo , Proteínas Amiloidogênicas/metabolismo , Benzotiazóis/química , Benzotiazóis/metabolismo , Dicroísmo Circular , Imuno-Histoquímica , Microscopia Eletrônica de Transmissão , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/metabolismo , Ligação Proteica , Multimerização Proteica , Deficiências na Proteostase/etiologia , Deficiências na Proteostase/metabolismo , Relação Quantitativa Estrutura-Atividade , Difração de Raios X
7.
Acta Neuropathol Commun ; 6(1): 70, 2018 07 31.
Artigo em Inglês | MEDLINE | ID: mdl-30064522

RESUMO

Tau is known for its pathological role in neurodegenerative diseases, including Alzheimer's disease (AD) and other tauopathies. Tau is found in many subcellular compartments such as the cytosol and the nucleus. Although its normal role in microtubule binding is well established, its nuclear role is still unclear. Here, we reveal that tau localises to the nucleolus in undifferentiated and differentiated neuroblastoma cells (SHSY5Y), where it associates with TIP5, a key player in heterochromatin stability and ribosomal DNA (rDNA) transcriptional repression. Immunogold labelling on human brain sample confirms the physiological relevance of this finding by showing tau within the nucleolus colocalises with TIP5. Depletion of tau results in an increase in rDNA transcription with an associated decrease in heterochromatin and DNA methylation, suggesting that under normal conditions tau is involved in silencing of the rDNA. Cellular stress induced by glutamate causes nucleolar stress associated with the redistribution of nucleolar non-phosphorylated tau, in a similar manner to fibrillarin, and nuclear upsurge of phosphorylated tau (Thr231) which doesn't colocalise with fibrillarin or nucleolar tau. This suggests that stress may impact on different nuclear tau species. In addition to involvement in rDNA transcription, nucleolar non-phosphorylated tau also undergoes stress-induced redistribution similar to many nucleolar proteins.


Assuntos
Nucléolo Celular/efeitos dos fármacos , Nucléolo Celular/metabolismo , Agonistas de Aminoácidos Excitatórios/farmacologia , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Ácido Glutâmico/farmacologia , Proteínas tau/metabolismo , Encéfalo/metabolismo , Encéfalo/ultraestrutura , Diferenciação Celular/fisiologia , Linhagem Celular Tumoral , Nucléolo Celular/ultraestrutura , Proteínas Cromossômicas não Histona/metabolismo , Proteínas Cromossômicas não Histona/ultraestrutura , DNA Ribossômico/genética , DNA Ribossômico/metabolismo , Regulação Neoplásica da Expressão Gênica/genética , Heterocromatina/fisiologia , Histonas/metabolismo , Humanos , Imunoprecipitação , Microscopia Confocal , Microscopia Eletrônica , Neuroblastoma/patologia , Neuroblastoma/ultraestrutura , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Transporte Proteico/efeitos dos fármacos , RNA Mensageiro , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/metabolismo , Transcrição Genética/efeitos dos fármacos , Transfecção , Proteínas tau/genética , Proteínas tau/ultraestrutura
8.
J Mol Biol ; 430(21): 4119-4131, 2018 10 19.
Artigo em Inglês | MEDLINE | ID: mdl-30121297

RESUMO

Alzheimer's disease is a tauopathy characterized by pathological fibrillization of tau protein to form the paired helical filaments (PHFs), which constitute neurofibrillary tangles. The methylthioninium (MT) moiety reverses the proteolytic stability of the PHF core and is in clinical development for treatment of Alzheimer's disease in a stable reduced form as leuco-MT. It has been hypothesized that MT acts via oxidation of cysteine residues, which is incompatible with activity in the predominantly reducing environment of living cells. We have shown recently that the PHF-core tau unit assembles spontaneously in vitro to form PHF-like filaments. Here we describe studies using circular dichroism, SDS-PAGE, transmission electron microscopy and site-directed mutagenesis to elucidate the mechanism of action of the MT moiety. We show that MT inhibitory activity is optimal in reducing conditions, that the active moiety is the reduced leuco-MT form of the molecule and that its mechanism of action is cysteine independent.


Assuntos
Cisteína/metabolismo , Azul de Metileno/análogos & derivados , Emaranhados Neurofibrilares/química , Emaranhados Neurofibrilares/metabolismo , Proteínas tau/química , Proteínas tau/metabolismo , Doença de Alzheimer/metabolismo , Doença de Alzheimer/patologia , Heparina/química , Humanos , Azul de Metileno/química , Estrutura Molecular , Emaranhados Neurofibrilares/ultraestrutura , Proteínas Recombinantes , Análise Espectral
9.
Front Cell Neurosci ; 12: 220, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30123109

RESUMO

Alzheimer's disease (AD) is the most common form of dementia and is distinguished from other dementias by observation of extracellular Amyloid-ß (Aß) plaques and intracellular neurofibrillary tangles, comprised of fibrils of Aß and tau protein, respectively. At early stages, AD is characterized by minimal neurodegeneration, oxidative stress, nucleolar stress, and altered protein synthesis machinery. It is generally believed that Aß oligomers are the neurotoxic species and their levels in the AD brain correlate with the severity of dementia suggesting that they play a critical role in the pathogenesis of the disease. Here, we show that the incubation of differentiated human neuroblastoma cells (SHSY5Y) with freshly prepared Aß42 oligomers initially resulted in oxidative stress and subtle nucleolar stress in the absence of DNA damage or cell death. The presence of exogenous Aß oligomers resulted in altered nuclear tau levels as well as phosphorylation state, leading to altered distribution of nucleolar tau associated with nucleolar stress. These markers of cellular dysfunction worsen over time alongside a reduction in ribosomal RNA synthesis and processing, a decrease in global level of newly synthesized RNA and reduced protein synthesis. The interplay between Aß and tau in AD remains intriguing and Aß toxicity has been linked to tau phosphorylation and changes in localization. These findings provide evidence for the involvement of Aß42 effects on nucleolar tau and protein synthesis machinery dysfunction in cultured cells. Protein synthesis dysfunction is observed in mild cognitive impairment and early AD in the absence of significant neuronal death.

10.
ACS Nano ; 12(9): 9101-9109, 2018 09 25.
Artigo em Inglês | MEDLINE | ID: mdl-30157375

RESUMO

Peptide self-assembly represents a powerful bottom-up approach to the fabrication of nanomaterials. ß3-Peptides are non-natural peptides composed entirely of ß-amino acids, which have an extra methylene in the backbone, and we reported fibers derived from the self-assembly of ß3-peptides that adopt 14-helical structures. ß3-Peptide assemblies represent a class of stable nanomaterials that can be used to generate bio- and magneto-responsive materials with proteolytic stability. However, the three-dimensional structure of many of these materials remains unknown. To develop structure-based criteria for the design of ß3-peptide-based biomaterials with tailored function, we investigated the structure of a tri-ß3-peptide nanoassembly by molecular dynamics simulations and X-ray fiber diffraction analysis. Diffraction data was collected from aligned fibrils formed by Ac-ß3[LIA] in water and used to inform and validate the model structure. Models with 3-fold radial symmetry resulted in stable fibers with a triple-helical coiled-coil motif and measurable helical pitch and periodicity. The fiber models revealed a hydrophobic core and twist along the fiber axis arising from a maximization of contacts between hydrophobic groups of adjacent tripeptides on the solvent-exposed fiber surface. These atomic structures of macroscale fibers derived from ß3-peptide-based materials provide valuable insight into the effects of the geometric placement of the side chains and the influence of solvent on the core fiber structure which is perpetuated in the superstructure morphology.


Assuntos
Nanofibras/química , Peptídeos/química , Materiais Biocompatíveis/química , Modelos Moleculares , Tamanho da Partícula , Conformação Proteica , Propriedades de Superfície
11.
Mol Microbiol ; 110(6): 897-913, 2018 12.
Artigo em Inglês | MEDLINE | ID: mdl-29802781

RESUMO

Bacterial biofilms are communities of microbial cells encased within a self-produced polymeric matrix. In the Bacillus subtilis biofilm matrix, the extracellular fibres of TasA are essential. Here, a recombinant expression system allows interrogation of TasA, revealing that monomeric and fibre forms of TasA have identical secondary structure, suggesting that fibrous TasA is a linear assembly of globular units. Recombinant TasA fibres form spontaneously, and share the biological activity of TasA fibres extracted from B. subtilis, whereas a TasA variant restricted to a monomeric form is inactive and subjected to extracellular proteolysis. The biophysical properties of both native and recombinant TasA fibres indicate that they are not functional amyloid-like fibres. A gel formed by TasA fibres can recover after physical shear force, suggesting that the biofilm matrix is not static and that these properties may enable B. subtilis to remodel its local environment in response to external cues. Using recombinant fibres formed by TasA orthologues we uncover species variability in the ability of heterologous fibres to cross-complement the B. subtilis tasA deletion. These findings are indicative of specificity in the biophysical requirements of the TasA fibres across different species and/or reflect the precise molecular interactions needed for biofilm matrix assembly.


Assuntos
Proteínas Amiloidogênicas/metabolismo , Bacillus subtilis/fisiologia , Proteínas de Bactérias/metabolismo , Biofilmes , Proteínas Amiloidogênicas/química , Proteínas Amiloidogênicas/genética , Bacillus subtilis/metabolismo , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Estrutura Secundária de Proteína , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo
12.
Interface Focus ; 7(6): 20170027, 2017 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-29147557

RESUMO

Amyloidogenic peptides are well known for their involvement in diseases such as type 2 diabetes and Alzheimer's disease. However, more recently, amyloid fibrils have been shown to provide scaffolding and protection as functional materials in a range of organisms from bacteria to humans. These roles highlight the incredible tensile strength of the cross-ß amyloid architecture. Many amino acid sequences are able to self-assemble to form amyloid with a cross-ß core. Here we describe our recent advances in understanding how sequence contributes to amyloidogenicity and structure. For example, we describe penta- and hexapeptides that assemble to form different morphologies; a 12mer peptide that forms fibrous crystals; and an eight-residue peptide originating from α-synuclein that has the ability to form nanotubes. This work provides a wide range of peptides that may be exploited as fibrous bionanomaterials. These fibrils provide a scaffold upon which functional groups may be added, or templated assembly may be performed.

13.
J Mol Biol ; 429(23): 3650-3665, 2017 11 24.
Artigo em Inglês | MEDLINE | ID: mdl-28919235

RESUMO

Alzheimer's disease is characterized by the self-assembly of tau and amyloid ß proteins into oligomers and fibrils. Tau protein assembles into paired helical filaments (PHFs) that constitute the neurofibrillary tangles observed in neuronal cell bodies in individuals with Alzheimer's disease. The mechanism of initiation of tau assembly into PHFs is not well understood. Here we report that a truncated 95-amino-acid tau fragment (corresponding to residues 297-391 of full-length tau) assembles into PHF-like fibrils in vitro without the need for other additives to initiate or template the process. Using electron microscopy, circular dichroism and X-ray fiber diffraction, we have characterized the structure of the fibrils formed from truncated tau for the first time. To explore the contribution of disulfide formation to fibril formation, we have compared the assembly of tau(297-391) under reduced and non-reducing conditions and for truncated tau carrying a C322A substitution. We show that disulfide bond formation inhibits filament assembly and that the C322A variant rapidly forms long and highly ordered PHFs.


Assuntos
Doença de Alzheimer/patologia , Peptídeos beta-Amiloides/química , Encéfalo/metabolismo , Reagentes para Ligações Cruzadas/química , Dissulfetos/química , Proteínas tau/química , Doença de Alzheimer/metabolismo , Peptídeos beta-Amiloides/metabolismo , Reagentes para Ligações Cruzadas/metabolismo , Dissulfetos/metabolismo , Humanos , Emaranhados Neurofibrilares , Proteínas tau/metabolismo
14.
Biomaterials ; 139: 195-201, 2017 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-28622603

RESUMO

Changes in microscopic viscosity and macromolecular crowding accompany the transition of proteins from their monomeric forms into highly organised fibrillar states. Previously, we have demonstrated that viscosity sensitive fluorophores termed 'molecular rotors', when freely mixed with monomers of interest, are able to report on changes in microrheology accompanying amyloid formation, and measured an increase in rigidity of approximately three orders of magnitude during aggregation of lysozyme and insulin. Here we extend this strategy by covalently attaching molecular rotors to several proteins capable of assembly into fibrils, namely lysozyme, fibrinogen and amyloid-ß peptide (Aß(1-42)). We demonstrate that upon covalent attachment the molecular rotors can successfully probe supramolecular assembly in vitro. Importantly, our new strategy has wider applications in cellulo and in vivo, since covalently attached molecular rotors can be successfully delivered in situ and will colocalise with the aggregating protein, for example inside live cells. This important advantage allowed us to follow the microscopic viscosity changes accompanying blood clotting and during Aß(1-42) aggregation in live SH-SY5Y cells. Our results demonstrate that covalently attached molecular rotors are a widely applicable tool to study supramolecular protein assembly and can reveal microrheological features of aggregating protein systems both in vitro and in cellulo not observable through classical fluorescent probes operating in light switch mode.


Assuntos
Compostos de Boro/química , Carbocianinas/química , Corantes Fluorescentes/química , Agregados Proteicos , Peptídeos beta-Amiloides/química , Linhagem Celular , Fibrinogênio/química , Humanos , Insulina/química , Microscopia Eletrônica de Transmissão , Sondas Moleculares , Muramidase/química , Nanoconjugados/química , Imagem Óptica , Fragmentos de Peptídeos/química , Viscosidade
15.
J Am Chem Soc ; 139(25): 8685-8692, 2017 06 28.
Artigo em Inglês | MEDLINE | ID: mdl-28578581

RESUMO

We report a peptide-based multichromophoric hydrogelator system, wherein π-electron units with different inherent spectral energies are spatially controlled within peptidic 1-D nanostructures to create localized energy gradients in aqueous environments. This is accomplished by mixing different π-conjugated peptides prior to initiating self-assembly through solution acidification. We can vary the kinetics of the assembly and the degree of self-sorting through the choice of the assembly trigger, which changes the kinetics of acidification. The hydrolysis of glucono-δ-lactone (GdL) provides a slow pH drop that allows for stepwise triggering of peptide components into essentially self-sorted nanostructures based on subtle pKa differences, whereas HCl addition leads to a rapid formation of mixed components within a nanostructure. Using 1H NMR spectroscopy and fiber X-ray diffraction, we determine the conditions and peptide mixtures that favor self-sorting or intimate comixing. Photophysical investigations in the solution phase provide insight into the correlation of energy-transport processes occurring within the assemblies to the structural organization of the π-systems.


Assuntos
Hidrogéis/química , Peptídeos/química , Cinética , Espectroscopia de Ressonância Magnética , Microscopia Eletrônica de Transmissão , Estrutura Molecular , Nanoestruturas/química , Difração de Raios X
17.
FEBS Lett ; 591(9): 1236-1246, 2017 05.
Artigo em Inglês | MEDLINE | ID: mdl-28337747

RESUMO

Amyloid-ß (Aß) peptides are implicated in the causation of memory loss, neuronal impairment, and neurodegeneration in Alzheimer's disease. Our recent work revealed that Aß 1-42 and Aß 25-35 inhibit long-term memory (LTM) recall in Lymnaea stagnalis (pond snail) in the absence of cell death. Here, we report the characterization of the active species prepared under different conditions, describe which Aß species is present in brain tissue during the behavioral recall time point and relate the sequence and structure of the oligomeric species to the resulting neuronal properties and effect on LTM. Our results suggest that oligomers are the key toxic Aß1-42 structures, which likely affect LTM through synaptic plasticity pathways, and that Aß 1-42 and Aß 25-35 cannot be used as interchangeable peptides.


Assuntos
Peptídeos beta-Amiloides/farmacologia , Lymnaea/efeitos dos fármacos , Memória de Longo Prazo/efeitos dos fármacos , Fragmentos de Peptídeos/farmacologia , Peptídeos beta-Amiloides/química , Peptídeos beta-Amiloides/ultraestrutura , Animais , Fenômenos Eletrofisiológicos/efeitos dos fármacos , Hemolinfa/efeitos dos fármacos , Hemolinfa/fisiologia , Lymnaea/fisiologia , Memória de Longo Prazo/fisiologia , Microscopia Eletrônica de Transmissão , Neurônios/efeitos dos fármacos , Neurônios/fisiologia , Técnicas de Patch-Clamp , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/ultraestrutura
18.
FEBS Lett ; 591(5): 822-830, 2017 03.
Artigo em Inglês | MEDLINE | ID: mdl-28185264

RESUMO

ß-amyloid 1-42 (Aß1-42) is a self-assembling peptide that goes through many conformational and morphological changes before forming the fibrils that are deposited in extracellular plaques characteristic of Alzheimer's disease. The link between Aß1-42 structure and toxicity is of major interest, in particular, the neurotoxic potential of oligomeric species. Many studies utilise reversed (Aß42-1) and scrambled (AßS) forms of amyloid-ß as control peptides. Here, using circular dichroism, thioflavin T fluorescence and transmission electron microscopy, we reveal that both control peptides self-assemble to form fibres within 24 h. However, oligomeric Aß reduces cell survival of hippocampal neurons, while Aß42-1 and Aßs have reduced effect on cellular health, which may arise from their ability to assemble rapidly to form protofibrils and fibrils.


Assuntos
Peptídeos beta-Amiloides/toxicidade , Amiloide/química , Proteínas Amiloidogênicas/toxicidade , Neurônios/efeitos dos fármacos , Fragmentos de Peptídeos/toxicidade , Sequência de Aminoácidos , Peptídeos beta-Amiloides/síntese química , Proteínas Amiloidogênicas/síntese química , Animais , Animais Recém-Nascidos , Benzotiazóis , Sobrevivência Celular/efeitos dos fármacos , Hipocampo/citologia , Hipocampo/efeitos dos fármacos , Hipocampo/metabolismo , Humanos , Neurônios/citologia , Neurônios/metabolismo , Fragmentos de Peptídeos/síntese química , Cultura Primária de Células , Conformação Proteica em Folha beta , Ratos , Espectrometria de Fluorescência , Tiazóis
19.
Soft Matter ; 13(9): 1914-1919, 2017 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-28186211

RESUMO

We show that the same low molecular weight gelator can form gels using three different methods. Gels were formed from a high pH solution either by adding a salt or by adding an acid; gels were also formed by adding water to a solution of the gelator in an organic solvent. The mechanical properties for the gels formed by the different methods are different from one another. We link this to the network type that is formed, as well as the fibrous structures that are formed. The salt-triggered gels show a significant number of fibres that tend to align. The acid-triggered gels contain many thin fibres, which form an entangled network. The solvent-triggered gels show the presence of spherulitic domains. We show that it is tractable to vary the trigger mechanism for an established, robust gelator to prepare gels with targeted properties as opposed to synthesising new gelators.

20.
J Nanobiotechnology ; 14(1): 79, 2016 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-27905946

RESUMO

BACKGROUND: A series of amyloidogenic peptides based on the sequence KFFEAAAKKFFE template the silica precursor, tetraethyl orthosilicate to form silica-nanowires containing a cross-ß peptide core. RESULTS: Investigation of the stability of these fibres reveals that the silica layers protect the silica-nanowires allowing them to maintain their shape and physical and chemical properties after incubation with organic solvents such as 2-propanol, ethanol, and acetonitrile, as well as in a strong acidic solution at pH 1.5. Furthermore, these nanowires were thermally stable in an aqueous solution when heated up to 70 °C, and upon autoclaving. They also preserved their conformation following incubation up to 4 weeks under these harsh conditions, and showed exceptionally high physical stability up to 1000 °C after ageing for 12 months. We show that they maintain their ß-sheet peptide core even after harsh treatment by confirming the ß-sheet content using Fourier transform infrared spectra. The silica nanowires show significantly higher chemical and thermal stability compared to the unsiliconised fibrils. CONCLUSIONS: The notable chemical and thermal stability of these silica nanowires points to their potential for use in microelectromechanics processes or fabrication for nanotechnological devices.


Assuntos
Nanofios/química , Peptídeos/química , Dióxido de Silício/química , Sequência de Aminoácidos , Temperatura Alta , Concentração de Íons de Hidrogênio , Microscopia Eletrônica de Transmissão , Nanofios/ultraestrutura , Peptídeos/síntese química , Conformação Proteica em Folha beta , Espectroscopia de Infravermelho com Transformada de Fourier , Termogravimetria
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