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1.
J Chem Theory Comput ; 15(9): 5087-5102, 2019 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-31402660

RESUMO

Circular dichroism (CD) spectroscopy is a highly sensitive but low-resolution technique to study the structure of proteins. Combined with molecular modeling or other complementary techniques, CD spectroscopy can provide essential information at higher resolution. To this end, we introduce a new computational method to calculate the electronic circular dichroism spectra of proteins from a structural model or ensemble using the average secondary structure composition and a precalculated set of basis spectra. The method is designed for model validation to estimate the error of a given protein structural model based on the measured CD spectrum. We compared the predictive power of our method to that of existing algorithms, namely, DichroCalc and PDB2CD, and found that it predicts CD spectra more accurately. Our results indicate that the derived basis sets are robust to both experimental errors in the reference spectra and the choice of the secondary structure classification algorithm. For over 80% of the globular reference proteins, our basis sets accurately predict the experimental spectrum solely from their secondary structure composition. For the remaining 20%, correcting for intensity normalization considerably improves the prediction power. Additionally, we show that the predictions for short peptides and an example complex of intrinsically disordered proteins strongly benefit from accounting for side-chain contributions and structural flexibility.


Assuntos
Dicroísmo Circular , Proteínas/química , Algoritmos , Modelos Moleculares , Conformação Proteica , Teoria Quântica
2.
Chem Commun (Camb) ; 55(70): 10432-10435, 2019 Aug 27.
Artigo em Inglês | MEDLINE | ID: mdl-31408066

RESUMO

RNA represents an extremely promising and yet challenging therapeutic target. Here, we report the design of a series of C-nucleosides as original RNA binders. Some of them bind strongly and selectively to A-site prokaryotic ribosomal RNA.


Assuntos
Nucleosídeos/metabolismo , RNA Ribossômico/metabolismo , Ribossomos/metabolismo , Dicroísmo Circular , Ressonância Magnética Nuclear Biomolecular , Conformação de Ácido Nucleico , Nucleosídeos/química , RNA Ribossômico/química , Termodinâmica
3.
Chem Biodivers ; 16(8): e1900317, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31264344

RESUMO

Four new diterpenoids named cuceolatins A-D, including three labdane-type (1-3) and one abietane-type (4) as well as three known labdane analogs (5-7), were reported from the leaves of Cunninghamia lanceolata. Structural assignments for these compounds were conducted by analyses of spectroscopic data, and their absolute configurations were determined by time-dependent density functional theory (TD-DFT) based electronic circular dichroism (ECD) calculations. Among them, the abietane-type diterpenoid (11-hydroxy-12-methoxyabieta-8,11,13-trien-3-one (4)) showed significant cytotoxicity against human MDA-MB-231, MCF-7, and HeLa tumor cell lines with IC50 measurements of 4.3, 2.8 and 4.5 µm, respectively, while the labdane-type diterpenoids with a 4α-carboxy group (1-3 and 5) exhibited moderate antibacterial activity towards Bacillus subtilis and Staphylococcus aureus with IC50 values all below 25 µm.


Assuntos
Cunninghamia/química , Diterpenos/química , Antineoplásicos Fitogênicos/química , Antineoplásicos Fitogênicos/isolamento & purificação , Antineoplásicos Fitogênicos/farmacologia , Bacillus subtilis/efeitos dos fármacos , Linhagem Celular Tumoral , Sobrevivência Celular/efeitos dos fármacos , Dicroísmo Circular , Cunninghamia/metabolismo , Teoria da Densidade Funcional , Diterpenos/isolamento & purificação , Diterpenos/farmacologia , Diterpenos de Abietano/química , Diterpenos de Abietano/isolamento & purificação , Diterpenos de Abietano/farmacologia , Humanos , Conformação Molecular , Folhas de Planta/química , Folhas de Planta/metabolismo , Staphylococcus aureus/efeitos dos fármacos
4.
Food Chem ; 298: 125060, 2019 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-31261004

RESUMO

Typical ketone flavours (with variations in chain length, position and number of keto group, branched chain) were selected to investigate the effect of molecule structure of ketones on their interactions with myofibrillar proteins (MPs). Results showed that 2,3-pentanedione quenched the fluorescence of MPs more effectively than 2-pentanone and 3-pentanone due to the number of keto group. There was no significant difference between 5-methyl-2-hexanone and 2-heptanone, which was attributed to their similar molecular size and polarity. The quenching effect of homologous ketone flavours increased with carbon chain growth due to the higher hydrophobic interaction. Dynamic quenching played a major role in the fluorescence quenching process of MPs by 2-pentanone, 3-pentanone, 5-methyl-2-hexanone, 2-heptanone and 2-octanone. The α-helix content decreased gradually with the increase of ketones concentration. Results of GC/MS were in accordance with the fluorescence quenching analysis generally, whereas 2,3-pentanedione and 2-nonanone exhibited some differences due to their higher steric hindrance effects.


Assuntos
Aromatizantes/química , Cetonas/química , Proteínas Musculares/química , Animais , Dicroísmo Circular , Aromatizantes/análise , Aromatizantes/metabolismo , Cromatografia Gasosa-Espectrometria de Massas , Cetonas/metabolismo , Proteínas Musculares/metabolismo , Ligação Proteica , Microextração em Fase Sólida , Espectrometria de Fluorescência , Suínos
5.
J Sci Food Agric ; 99(13): 5881-5889, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31206698

RESUMO

BACKGROUND: The suppression of α-glucosidase activity to retard glucose absorption is an important therapy for type-2 diabetes. Corosolic acid (CRA) is a potential antidiabetic component in many plant-based foods and herbs. In this study, the interplay mechanism between α-glucosidase and corosolic acid was investigated by several methods, including three-dimensional fluorescence spectra, circular dichroism spectra, and molecular simulation. RESULTS: Corosolic acid significantly inhibited α-glucosidase reversibly in an uncompetitive manner and its IC50 value was 1.35 × 10-5 mol L-1 . A combination of CRA with myricetin exerted a weak synergy against α-glucosidase. The intrinsic fluorescence of α-glucosidase was quenched via a static quenching course and the binding constant was 3.47 × 103 L mol-1 at 298 K. The binding of CRA to α-glucosidase was mainly driven by hydrophobic forces and resulted in a partial extension of the protein polypeptide chain with a loss of α-helix content. The molecular simulation illustrated that CRA bound to the entrance part of the active center of α-glucosidase and interacted with the amino acid residues Ser157, Arg442, Phe303, Arg315, Tyr158, and Gln353, which could hinder the release of substrate and catalytic reaction product, eventually suppressing the catalytic activity of α-glucosidase. CONCLUSIONS: These results may suggest new insights into corosolic acid from food sources as a potential α-glucosidase inhibitor that could better control diabetes. © 2019 Society of Chemical Industry.


Assuntos
Inibidores Enzimáticos/química , Triterpenos/química , alfa-Glucosidases/química , Motivos de Aminoácidos , Sítios de Ligação , Dicroísmo Circular , Humanos , Hipoglicemiantes/química , Simulação de Acoplamento Molecular
6.
Biochemistry (Mosc) ; 84(5): 562-569, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-31234770

RESUMO

Amplification of GC-rich regions of genomic DNA is hindered either by high stability of DNA double helix or as a result of alternative structure formation by a guanine-rich DNA strand. Such potential G-quadruplex (G4) sequences are fairly common in promoters of the human genome. The efficiency of PCR amplification of promoter sequences for several human oncogenes (MYC, NRAS, TERT, KRAS, KIT) was studied. We demonstrate that the efficiency of DNA polymerase is reduced in the presence of potassium ions. The primer-extension technique localized DNA polymerase stops at the 3'-ends of potential quadruplex sequences. The structural and thermodynamic properties of short G-rich oligonucleotides corresponding to the stops of DNA polymerase were analyzed. These oligonucleotides formed stable parallel G4 in the presence of potassium ions. Correlation between the stability of G4 structure and efficiency of DNA polymerase stops was revealed. The results provide a method for detecting new G4 structures in extended genomic sequences and also clarify the mechanism of inhibition of DNA polymerase in G-rich regions of DNA.


Assuntos
DNA Polimerase Dirigida por DNA/metabolismo , Quadruplex G , Potássio/metabolismo , Dicroísmo Circular , DNA Polimerase Dirigida por DNA/química , Oligonucleotídeos/metabolismo , Reação em Cadeia da Polimerase , Potássio/química , Regiões Promotoras Genéticas , Proteínas Proto-Oncogênicas c-myc/genética , Termodinâmica , Proteínas ras/genética
7.
Anal Bioanal Chem ; 411(21): 5555-5561, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31197422

RESUMO

G-quadruplexes have been widely researched as new targets for cancer treatment owing to their non-canonical structure and crucial role in biological processes. Although attention has been paid to the development of selective G-quadruplex ligands, few studies have focused on the binding affinity of stereoisomers towards G-quadruplex, which will be conducive to support the optimal design of G-quadruplex ligands in future studies. Here, tetrandrine and isotetrandrine were used to study the binding affinity and difference of stereoisomers towards G-quadruplex structures. The results showed that tetrandrine had a high possibility of binding to the N-myc and Bcl-2 G-quadruplexes through hydrogen bonding, whereas the possibility of binding of isotetrandrine was low and it seemed to have no possibility of forming hydrogen bonds. Our study shows that optical isomerism of ligand molecules has an important effect on G-quadruplex recognition, which is helpful for the design of G-quadruplex ligands in future studies. Graphical abstract.


Assuntos
Alcaloides/metabolismo , Quadruplex G , Benzilisoquinolinas/química , Benzilisoquinolinas/metabolismo , Dicroísmo Circular , Ligações de Hidrogênio , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , Proteínas Proto-Oncogênicas c-myc/metabolismo , Espectrometria de Massas por Ionização por Electrospray , Estereoisomerismo , Termodinâmica
8.
Planta Med ; 85(13): 1088-1097, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31216579

RESUMO

As part of our search for new cytotoxic and antimicrobial natural products from endolichenic fungi, 19 compounds including 1 new 10-member lactone (2: ), 1 new polyacetylene glycoside (3: ), 1 new brasilane-type sesquiterpenoid glycoside (4: ), and 2 isobenzofuran-1(3H)-one derivatives (5: and 6: ) were isolated from the solid culture of the endolichenic fungus Hypoxylon fuscum. Their structures were unambiguously elucidated by NMR spectroscopic data, MS, ECD (electronic circular dichroism) calculation, and chemical methods. The cytotoxic effects on K562, SW480, and HEPG2 cell lines and the antimicrobial activity against Bacillus subtilis, Staphylococcus aureus, Escherichia coli, and Candida albicans were assessed. Compounds 1, 2: , and 5: exhibited moderate cytotoxicity against K562, SW480, and HEPG2 cell lines while compounds 1, 9: , and 11: displayed weak antibacterial activity against S. aureus.


Assuntos
Citotoxinas/isolamento & purificação , Xylariales/metabolismo , Anti-Infecciosos/isolamento & purificação , Anti-Infecciosos/farmacologia , Bacillus subtilis/efeitos dos fármacos , Candida albicans/efeitos dos fármacos , Linhagem Celular Tumoral/efeitos dos fármacos , Dicroísmo Circular , Citotoxinas/farmacologia , Escherichia coli/efeitos dos fármacos , Células Hep G2/efeitos dos fármacos , Humanos , Células K562/efeitos dos fármacos , Espectroscopia de Ressonância Magnética , Staphylococcus aureus/efeitos dos fármacos , Xylariales/química
9.
Food Chem ; 297: 125021, 2019 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-31253338

RESUMO

In this study, the effects of ultrasonic intensity on conformational changes in aqueous citrus pectin solution under ultrasonic processing and its possible transition mechanism were investigated. The results demonstrated that higher ultrasonic intensity (104.7 W/cm2) caused larger alterations in the molecular and conformational parameters of the semiflexible pectin (Mark-Houwink relation exponent a: 0.820, conformational parameter α: 0.607, structural parameter ρ: 2.22) in aqueous solution. Meanwhile, the semiflexible chain of pectin became more flexible (a: 0.804, α: 0.601, ρ: 1.75) at higher ultrasonic intensity in aqueous solution, as was verified by atomic force microscopy. Moreover, conformational changes in pectin from semiflexible chains to flexible chains or even flexible coils (a: 0.791, α: 0.597, ρ: 1.70) could be attributed to the decreased degree of methoxylation and neutral sugars in side chains and the destruction of inter- and intramolecular hydrogen bonds under ultrasonic processing. Therefore, these results have important implications for understanding the ultrasonic modification of pectin.


Assuntos
Citrus/metabolismo , Pectinas/química , Configuração de Carboidratos , Cromatografia Líquida de Alta Pressão , Dicroísmo Circular , Ligações de Hidrogênio , Microscopia de Força Atômica , Sonicação , Açúcares/química , Viscosidade
10.
Biochemistry (Mosc) ; 84(6): 672-685, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-31238867

RESUMO

Mature pore-forming OmpF protein from the outer membrane of Yersinia pseudotuberculosis was expressed in Escherichia coli in the form of inclusion bodies (IBs) under different cultivation conditions. The properties and structural organization of the IBs as well as the structure of the recombinant porin (rOmpF) solubilized from the IBs were investigated using electron microscopy, dynamic light scattering, optical spectroscopy, and specific hydrophobic dyes. The size, shape, and stability of the IBs under denaturing solutions were determined. It was found that the IBs were readily soluble in SDS and more resistant to urea. Dissolution of the IBs in both denaturing agents led to formation of a heterogeneous in size population of oligomeric particles. The IBs contained an intermediate form of the rOmpF with native-like secondary structure and elements of tertiary structure, which was able to penetrate a lipid bilayer and adopt a functionally active conformation. There were no significant differences in the properties and structure between the examined IBs formed at different concentrations of the inducer (IPTG). However, the content of amyloids in the IBs increased with increasing concentration of the inducer. These results contribute to the development of new approaches for the production of active proteins from IBs, as well as biologically and functionally active IBs.


Assuntos
Proteínas da Membrana Bacteriana Externa/metabolismo , Corpos de Inclusão/metabolismo , Porinas/metabolismo , Yersinia pseudotuberculosis/metabolismo , Proteínas da Membrana Bacteriana Externa/química , Dicroísmo Circular , Eletroforese em Gel de Poliacrilamida , Temperatura Alta , Microscopia Eletrônica de Varredura , Porinas/química , Conformação Proteica , Proteínas Recombinantes/química , Proteínas Recombinantes/metabolismo , Solubilidade , Espectrometria de Fluorescência , Espectrofotometria Ultravioleta
11.
Food Chem ; 295: 120-128, 2019 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-31174740

RESUMO

This research investigated the effects of commonly practiced thermal treatments (simulated pasteurization, retort sterilization and UHT sterilization) on peanut protein isolate (PPI)-glucose solution. Results showed that thermal treatment on PPI-glucose solution from mild to drastic conditions would lead to a more ordered and compact protein structure, greater extent of Maillard reaction, higher degree of graft, stronger in vitro antioxidant activities, but decrease in vitro digestion especially lower degree of hydrolysis in two-step enzymolysis by pepsin and then pancreatin. Compared with the unheated PPI-glucose solution, the Td values of ones autoclaved at 121 °C for 30 min and 45 min increased by 5% and 12%, and the ΔH of all the heated samples was lower than the unheated one. The present study indicated that retort sterilization or UHT sterilization treatment could be favourable in producing a beverage containing PPI and glucose with proper digestibility and post-digestion antioxidant activities.


Assuntos
Arachis/metabolismo , Glucose/química , Proteínas de Plantas/metabolismo , Antioxidantes/química , Varredura Diferencial de Calorimetria , Dicroísmo Circular , Hidrólise , Reação de Maillard , Pasteurização , Pepsina A/metabolismo , Proteínas de Plantas/química , Estrutura Terciária de Proteína , Temperatura Ambiente
12.
Sci Total Environ ; 686: 1039-1048, 2019 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-31200302

RESUMO

2,7-Dibromocarbazole (2,7-DBCB) and 3,6-dibromocarbazole (3,6-DBCB) are emerging environmental pollutants, being potentially high risks to human health. In this study, interactions of the two compounds with human serum albumin (HSA) and bovine serum albumin (BSA) were investigated by molecular modeling, density functional theory calculations (DFT) and multispectral techniques. The static quenching interaction deduced in the fluorescence quenching experiment is confirmed by the time-resolved analyses. The interactions of the two compounds with HSA/BSA induce molecular microenvironment and conformation changes, as assessed by synchronous and 3D fluorescence spectra, together with a destruction of polypeptide carbonyl hydrogen bond network by circular dichroism and Fourier transform infrared analyses. The thermodynamic analysis indicated that the spontaneous interaction was hydrogen bonding and hydrophobic forces. The binding constant Ka at 298 K was 3.54 × 105 M-1 in HSA-2,7-DBCB, 6.63 × 105 M-1 in HSA-3,6-DBCB, 1.32 × 105 M-1 in BSA-2,7-DBCB and 2.17 × 105 M-1 in BSA-3,6-DBCB. These results indicates that 3,6-DBCB binds HSA/BSA more strongly than 2,7-DBCB, which was estimated with DFT calculations. Site marker competition experiments coupled with molecular modeling studies confirmed that both compounds bind HSA/BSA at site I (subdomain IIA). The results suggest that interactions between 2,7-DBCB and 3,6-DBCB with HSA and BSA may affect the normal physiological activities in human and animals.


Assuntos
Carbazóis/química , Poluentes Ambientais/química , Modelos Moleculares , Soroalbumina Bovina/química , Animais , Dicroísmo Circular , Teoria da Densidade Funcional , Fluorescência , Humanos , Ligações de Hidrogênio , Interações Hidrofóbicas e Hidrofílicas , Albumina Sérica , Termodinâmica
13.
Eur Biophys J ; 48(6): 523-537, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31203415

RESUMO

In this study we examined microenvironment of Trp residues in "dry" sets of nonhomologous proteins that belong to four structural classes, as well as in a "wet" set. In silico experiments showed that residues of Trp demonstrate higher surface accessibility in proteins of "alpha/beta" class where they are rarely included in beta strands. However, this feature has not caused "red" shift in fluorescence spectra in "alpha/beta" proteins in vitro, since there are several factors that should be combined together to cause it: high surface accessibility and high hydrophilicity of the microenvironment, the presence of destabilizing contacts with Asp, Asn, Leu, and multiple Tyr residues, as well as the lack of stabilizing interactions with Arg, Thr, and Pro. The occurrence of Trp residues has the highest value in beta-structural proteins, while they are not involved in aromatic-aromatic interactions with each other as frequently, as they do in proteins of "alpha + beta" class in which Trp residues are overrepresented near each other in the primary sequence. That is why the deformation of circular dichroism spectra because of Trp-Trp interactions is expected to be more frequent in proteins of "alpha + beta" class. In all four classes of proteins Trp residues are involved in long-range interactions with some hydrophobic (Leu, Val, Ile) and aromatic residues (Trp, Phe, and Tyr) more frequently than it is expected. They are involved in long-range interactions with some hydrophilic residues (Asp, Glu, Ser, and Lys) rarely than it is expected. Short-range interactions between Arg and Trp are overrepresented just in alpha-helical proteins.


Assuntos
Dicroísmo Circular , Proteínas/química , Espectrometria de Fluorescência , Triptofano , Interações Hidrofóbicas e Hidrofílicas
14.
Artigo em Inglês | MEDLINE | ID: mdl-31044667

RESUMO

The interaction of SnMe2Cl2(bu2bpy)complex with calf thymus DNA (ct-DNA) has been explored following, using spectroscopic methods, viscosity measurements, Atomic force microscopy, Thermal denaturation and Molecular docking. It was found that Sn(IV) complex could bind with DNA via intercalation mode as evidenced by hyperchromism and bathochromic in UV-Vis spectrum; these spectral characteristics suggest that the Sn(IV) complex interacts with DNA most likely through a mode that involves a stacking interaction between the aromatic chromophore and the base pairs of DNA. In addition, the fluorescence emission spectra of intercalated methylene blue (MB) with increasing concentrations of SnMe2Cl2(bu2bpy) represented a significant increase of MB intensity as to release MB from MB-DNA system. Positive values of ΔH and ΔS imply that the complex is bound to ct-DNA mainly via the hydrophobic attraction. Large complexes contain the DNA chains with an average size of 859 nm were observed by using AFM for Sn(IV) Complex-DNA. The Fourier transform infrared study showed a major interaction of Sn(IV) complex with G-C and A-T base pairs and a minor perturbation of the backbone PO2 group. Addition of the Sn(IV)complex results in a noticeable rise in the Tm of DNA. In addition, the results of viscosity measurements suggest that SnMe2Cl2(bu2bpy) complex may bind with the classical intercalative mode. From spectroscopic and hydrodynamic studies, it has been found that Sn(IV)complex interacts with DNA by intercalation mode. Optimized docked model of DNA-complex mixture confirmed the experimental results.


Assuntos
DNA/química , Microscopia de Força Atômica , Simulação de Acoplamento Molecular , Compostos Orgânicos de Estanho/química , Animais , Bovinos , Dicroísmo Circular , Estrutura Molecular , Espectrometria de Fluorescência , Espectrofotometria Ultravioleta , Termodinâmica
15.
Nat Commun ; 10(1): 2034, 2019 05 02.
Artigo em Inglês | MEDLINE | ID: mdl-31048691

RESUMO

Polyglutamine (polyQ) tracts are regions of low sequence complexity frequently found in transcription factors. Tract length often correlates with transcriptional activity and expansion beyond specific thresholds in certain human proteins is the cause of polyQ disorders. To study the structural basis of the association between tract length, transcriptional activity and disease, we addressed how the conformation of the polyQ tract of the androgen receptor, associated with spinobulbar muscular atrophy (SBMA), depends on its length. Here we report that this sequence folds into a helical structure stabilized by unconventional hydrogen bonds between glutamine side chains and main chain carbonyl groups, and that its helicity directly correlates with tract length. These unusual hydrogen bonds are bifurcate with the conventional hydrogen bonds stabilizing α-helices. Our findings suggest a plausible rationale for the association between polyQ tract length and androgen receptor transcriptional activity and have implications for establishing the mechanistic basis of SBMA.


Assuntos
Atrofia Bulboespinal Ligada ao X/genética , Peptídeos/química , Conformação Proteica em alfa-Hélice/genética , Receptores Androgênicos/química , Fatores de Transcrição/química , Atrofia Bulboespinal Ligada ao X/patologia , Dicroísmo Circular , Glutamina/química , Humanos , Hidrogênio/química , Ligações de Hidrogênio , Espectroscopia de Ressonância Magnética , Simulação de Dinâmica Molecular , Mutação , Agregados Proteicos/genética , Receptores Androgênicos/genética , Fatores de Transcrição/genética
16.
Eur Biophys J ; 48(4): 395-403, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-31053922

RESUMO

Optical properties of flavin adenine dinucleotide (FAD) moiety are widely used nowadays for biotechnological applications. Given the fundamental role played by FAD, additional structural information about this enzymatic cofactor can be extremely useful in order to obtain a greater insight into its functional role in proteins. For this purpose, we have investigated FAD behaviour in aqueous solutions at different pH values by a novel approach based on the combined use of time-resolved fluorescence and circular dichroism spectroscopies. The results showed that pH strongly affects time-resolved fluorescence emission and the analysis allowed us to detect a three-component decay for FAD in aqueous solution with pH-depending lifetimes and relative amplitudes. Circular dichroism data were analyzed by a multi-Gaussian fitting procedure and the trends of properly chosen parameters confirmed pH-depending changes. The comparison between the results obtained by these two optical techniques allowed us to improve the significance of the outcome of circular dichroism. This combined approach may provide a useful tool for biotechnological investigation.


Assuntos
Flavina-Adenina Dinucleotídeo/química , Conformação Molecular , Dicroísmo Circular , Concentração de Íons de Hidrogênio , Espectrometria de Fluorescência , Fatores de Tempo
17.
Food Chem ; 292: 188-196, 2019 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-31054664

RESUMO

Soy protein isolate (SPI) and sugar beet pectin (SBP) were adopted to fabricate double network (DN) gels via thermal treatment and laccase-catalysis. The concentrations of SBP (0.5%-2.5%, w/w) and SPI (4%-8%, w/w) were evaluated. DN gels showed higher holding water capacity (WHC, above 83%), compared with SBP single gel (75.96%). The presence of SPI improved the mechanical properties of gels significantly. Apparent phase separation could be observed when SPI concentration was 4%. Moreover, interpenetrating networks gradually formed with the increase of SPI concentration. The favorable structural heterogeneity and mechanical integrity derived from these polymers might be mainly responsible for the enhancement of the mechanical properties. The presence of SBP and laccase could improve the ß-sheet amounts of SPI and make it form more rigid structure according to the results of circular dichroism (CD) and fluorescence spectra. The excellent performance of DN gels could enable the delivery of various components.


Assuntos
Géis/química , Lacase/metabolismo , Pectinas/química , Proteínas de Soja/química , Beta vulgaris/metabolismo , Biocatálise , Dicroísmo Circular , Emulsões/química , Pectinas/metabolismo , Conformação Proteica em Folha beta , Reologia , Proteínas de Soja/metabolismo , Temperatura Ambiente , Água/química
18.
Chemphyschem ; 20(12): 1567-1571, 2019 Jun 17.
Artigo em Inglês | MEDLINE | ID: mdl-31087509

RESUMO

The thermodynamic stability of a cytosine(C)-rich i-motif tract of DNA, which features pH-sensitive [C..H..C]+ moieties, has been studied as function of both pressure (0.1-200 MPa) and pH (3.7-6.2). Careful attention was paid to correcting citrate buffer pH for known variations that stem from changes in pressure. Once pH-corrected, (i) at pH >4.6 the i-motif becomes less stable as pressure is increased (KD decreases), giving a small negative volume change for dissociation (ΔD V°) of the i-motif - a conclusion opposite to that which would be drawn if the buffer pH was not corrected for the effects of pressure; (ii) the i-motif's melting temperature increases by more than 30 K between pH 6.5 and 4.5, the consequence of an enthalpy for dissociation (ΔD H°) of 77(3) and 90(3) kJ (mol H+ )-1 at 0.1 and 200 MPa, respectively; (iii) below pH 4.6 at 0.1 MPa (pH 4.3 at 200 MPa) the melting temperature decreases as a result of double protonation of cytosine pairs, and ΔD H° and ΔD V° change signs; and (iv) the combination of ΔD H° and ΔD V° lead to the melting temperature at pH 4.3 being 3 K higher at 200 MPa than at 0.1 MPa.


Assuntos
DNA/química , Sequência de Bases , Dicroísmo Circular , Concentração de Íons de Hidrogênio , Espectroscopia de Ressonância Magnética , Conformação de Ácido Nucleico , Pressão , Termodinâmica , Temperatura de Transição
19.
Chem Commun (Camb) ; 55(42): 5882-5885, 2019 May 25.
Artigo em Inglês | MEDLINE | ID: mdl-31037281

RESUMO

Spinach aptamer fluorescence requires formation of a tripartite complex composed of folded RNA, a GFP-like fluorophore, and selective cation coordination. 2'F pyrimidine modified Spinach has retained fluorescence, increased chemical stability, and accelerated cation association via increased G-quadruplex dynamics, thereby reducing readout time and enhancing Spinach utility for aqueous Pb2+ detection.


Assuntos
Aptâmeros de Nucleotídeos/química , Chumbo/química , Ribose/química , Cátions Bivalentes , Dicroísmo Circular , Fluorescência , Corantes Fluorescentes/química , Quadruplex G , Técnicas In Vitro , Conformação de Ácido Nucleico , Espectrometria de Fluorescência
20.
Mar Drugs ; 17(5)2019 Apr 26.
Artigo em Inglês | MEDLINE | ID: mdl-31035506

RESUMO

Three new diketopiperazine alkaloids, including two oxepine-containing diketopiperazines, chrysopiperazines A and B (1 and 2), and one quinazoline-containing diketopiperazine, chrysopiperazine C (5), together with three known analogues (3, 4, and 6), were isolated from the gorgonian-derived Penicillium chrysogenum fungus. The relative and absolute configurations of C-3 and C-15 in 1 and 2, C-3 and C-14 in 5 were established by NOE modified Marfey's analysis and electronic circular dichroism (ECD) calculations. Particularly, the absolute configurations of C-19 in 1 and 3, which was very challenging to be identified due to the flexible conformation in a short aliphatic chain, were successfully determined by the vibrational circular dichroism (VCD) method, supplying with a reliable and optional method to define the absolute configurations. Additionally, this is the first report on oxepine-containing diketopiperazines from the genus Penicillium.


Assuntos
Alcaloides/química , Antozoários/microbiologia , Dicetopiperazinas/química , Penicillium chrysogenum/química , Alcaloides/isolamento & purificação , Alcaloides/farmacologia , Animais , Antibacterianos/química , Antibacterianos/isolamento & purificação , Antibacterianos/farmacologia , Antifúngicos/química , Antifúngicos/isolamento & purificação , Antifúngicos/farmacologia , Bactérias/efeitos dos fármacos , Dicroísmo Circular , Dicetopiperazinas/isolamento & purificação , Dicetopiperazinas/farmacologia , Fungos/efeitos dos fármacos , Testes de Sensibilidade Microbiana , Conformação Molecular , Estrutura Molecular , Espectroscopia de Prótons por Ressonância Magnética
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