CD Data Research Articles

SDBS induces multiple catalase conformations in a dose-dependent manner

Amyloid fibrils have been linked to several incurable diseases. They are long and thin fibrous proteins that self-assemble into fibrils. Small molecules can stimulate amyloid fibrillation, but the mechanism by which this happens is not well understood. This study examined how a negatively charged benzene ring containing surfactant, sodium dodecylbenzene sulphonate (SDBS), affects the fibrillation of bovine liver catalase (BLC). After SDBS treatment, BLC conformational changes were examined in vitro using turbidity, RLS kinetics, intrinsic fluorescence, ThT fluorescence, far-UV CD, and TEM. BLC in the native state was alpha-helical at pH 7.4, while it was converted to a random coil structure at pH 2.0. Far-UV CD and intrinsic fluorescence data showed that at concentrations <0.1 mM of SDBS, randomly coiled BLC assumed a native-like alpha-helical structure. However, between 0.1 and 1.0 mM SDBS, BLC was aggregated. ThT fluorescence and far-UV CD measurements showed the amyloid-like structures in the aggregated BLC. At higher SDBS concentrations (>1.0 mM) at pH 2.0, BLC again attains a native-like alpha-helical structure. It is essential for therapeutic purposes to clearly understand the process underlying surfactant- or lipid-induced fibrillation.

Phytochemical and chemotaxonomic studies on Pteris plumbea Christ

A phytochemical investigation on Pteris plumbea Christ led to the isolation of 19 compounds, including four diterpenoids (1–4), five sesquiterpenoids (5–9), eight flavonoids (10–17), and two lignans (18–19). The chemical structures of these compounds were elucidated by ORD, CD, MS, and NMR data. All of them were found from P. plumbea for the first time. Noticeably, compounds diosmetin (10), genkwanin (11), luteolin-7-O-rhamnoside (16), genistein 7-O-gentiobioside (17), and (+)-medioresinol (19) have not been reported from the family Pteridaceae. Meanwhile, the chemotaxonomic significance of the isolated compounds was summarized.

Potential natural product 3,4-seco-schitriterpenoids from Kadsura japonica L. as anti-neuroinflammatory agents

In the present study, the undescribed schitriterpenoids, kadsujanonols A−I (1–9), and eleven reported compounds (10–20) were isolated from K. japonica L. vines. Their structures of 3,4-seco-schitriterpenoids were elucidated mainly by spectroscopic analyses including 1H-, 13C-, and 2D-NMR, IR, HRESIMS spectra. The spatial configurations were determined by the single-crystal X-ray diffraction analysis of kadsujapnonol A (1), 15, 17, and 18, CD data and computational analysis. Furthermore, all isolates were evaluated for the anti-neuroinflammatory activity on LPS-stimulated NO production in BV2 microglial cells and compounds 2, 4, 5, 7, 9, 11, 13–16, and 18 exposed better or comparable suppression abilities than PDTC. Among them, kadlongilactone B (14) showed the best significant inhibiting ability (IC50 = 0.87 μg/mL) and the effect is through the attenuation of the inflammatory transcription factor p65NF-κB. Preliminary structure–activity relationship revealed that δ-lactone at the side chain and 7-member lactone at C-3/C-4, and 3,4:9,10 ring opening are important.

Bovine liver catalase turns into three conformational states after exposure to an anionic surfactant.

The mechanism by which anionic surfactants promote amyloid fibril is not well understood. Here, we investigated how sodium dodecyl sulfate (SDS), a negatively charged surfactant, affects the fibrillation of the partially unfolded random-coiled bovine liver catalase (BLC) at a pH of 2.0. We used several methods, including turbidity, RLS kinetics, intrinsic fluorescence, ThT fluorescence, far-UV CD, and TEM imaging, to evaluate the conformational changes of BLC in vitro in response to SDS treatment. BLC is a multimeric protein and well folded at physiological pH but forms a random coil structure at pH 2.0. Intrinsic fluorescence and far-UV CD data showed that below 0.1mM SDS, random coiled BLC turned into a native-like structure. BLC incubated with an SDS concentration ranging from 0.1 to 2.0mM led to the formation of aggregates. The ThT fluorescence intensity was enhanced in the aggregated BLC samples (0.1-2.0mM SDS), and cross beta-sheeted structure was detected by the far UV CD measurements. BLC adopts a complete alpha-helical structure upon interacting with SDS at a more than 2.0mM concentration at pH 2.0. Understanding the mechanism of surfactant- or lipid-induced fibrillation is important for therapeutic purposes.

Absolute configuration reassignment of nectamazin A: Implications to related neolignans

The ability of nature to produce structurally complex molecules makes the determination of the absolute configuration of natural products a challenging task. Although extensive NMR analysis generally allows for the reliable assignment of relative configurations, the assignments of absolute stereochemistry are commonly performed by empirical comparisons of optical rotation (OR) and/or electronic circular dichroism (ECD) data obtained for related molecules. Such an approach, however, may lead to misassignments and consequent error propagations. Herein, we present the case of the bicyclo(3.2.1)octane neolignan named (+)-nectamazin A. This compound was first reported in 2009 from Nectandra amazonum Nees. (Lauraceae) and had its absolute configuration determined as 7R,8S,3′S,4′R,5′S by means of experimental ECD spectroscopy. Our chemical studies on Ocotea aciphylla (Lauraceae) led to the isolation of (+)-nectamazin A. The extensive analysis of OR, ECD, and vibrational CD data aided by quantum chemical calculations, however, indicated (+)-nectamazin A to have the 7S,8R,3′R,4′S,5′R absolute configuration, in conflict with the configuration reported in the literature. The cause of the original incorrect assignment of (+)-nectamazin A derives from the direct comparison of experimental OR and ECD data obtained for structurally related molecules with different chromophoric systems. As an alternative, VCD spectroscopy is presented as a more reliable and sensitive technique to stereochemical investigations of bicyclo(3.2.1)octane neolignans.

Purification, Conformational Analysis and Cytotoxic Activities of Host-Defense Peptides from the Giant Gladiator Treefrog Boana boans (Hylidae: Hylinae).

Frogs from the extensive amphibian family Hylidae are a rich source of peptides with therapeutic potential. Peptidomic analysis of norepinephrine-stimulated skin secretions from the Giant Gladiator Treefrog Boana boans (Hylidae: Hylinae) collected in Trinidad led to the isolation and structural characterization of five host-defense peptides with limited structural similarity to figainin 2 and picturin peptides from other frog species belonging to the genus Boana. In addition, the skin secretions contained high concentrations of tryptophyllin-BN (WRPFPFL) in both C-terminally α-amidated and non-amidated forms. Figainin 2BN (FLGVALKLGKVLG KALLPLASSLLHSQ) and picturin 1BN (GIFKDTLKKVVAAVLTTVADNIHPK) adopt α-helical conformations in trifluroethanol-water mixtures and in the presence of cell membrane models (sodium dodecylsulfate and dodecylphosphocholine micelles). The CD data also indicate contributions from turn structures. Both peptides and picturin 2BN (GLMDMLKKVGKVALT VAKSALLP) inhibited the growth of clinically relevant Gram-negative and Gram-positive bacteria with MIC values in the range 7.8-62.5 µM. Figainin 2BN was potently cytotoxic to A549, MDA-MB-231 and HT-29 human tumor-derived cells (LC50 = 7-14 µM) but displayed comparable potency against non-neoplastic HUVEC cells (LC50 = 15 µM) indicative of lack of selectivity for cancer cells.

Cellulose nanocrystals derived from chicory plant: an un-competitive inhibitor of aromatase in breast cancer cells via PI3K/AKT/mTOP signalling pathway

A significant contributing factor in the development of breast cancer is the estrogens. The synthesis of estrogens is primarily facilitated by aromatase (CYP19), a cytochrome P450 enzyme. Notably, aromatase is expressed at a higher level in human breast cancer tissue compared with the normal breast tissue. Therefore, inhibiting aromatase activity is a potential strategy in hormone receptor-positive breast cancer treatment. In this study, Cellulose Nanocrystals (CNCs) were obtained from Chicory plant waste through a sulfuric acid hydrolysis method with the objective of investigating that whether the obtained CNCs could act as an inhibitor of aromatase enzyme, and prevent the conversion of androgens to estrogens. Structural analysis of CNCs was carried out using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), while morphological results were obtained using AFM, TEM, and FE-SEM. Furthermore, the nano-particles were found to be spherical in shape with a diameter range of 35-37 nm and displayed a reasonable negative surface charge. Stable transfection of MCF-7 cells with CYP19 has demonstrated the ability of CNCs to inhibit aromatase activities and prevent cell growth by interfering with the enzyme activities. Spectroscopic results revealed the binding constant of CYP19-CNCs and (CYP19-Androstenedione)-CNCs complexes to be 2.07 × 103 L/gr and 2.06 × 104 L/gr, respectively. Conductometry and CD data reported different interaction behaviors among CYP19 and CYP19-Androstenedione complexes at the presence of CNCs in the system. Moreover, the addition of CNCs to the solution in a successive manner resulted in the enhancement of the secondary structure of the CYP19-androstenedione complex. Additionally, CNCs showed a marked reduction in the viability of cancer cells compared to normal cells by enhancing the expression of Bax and p53 at protein and mRNA levels, and by decreasing mRNA levels of PI3K, AKT, and mTOP, as well as protein levels of PI3Kg-P110 and P-mTOP, in MCF-7 cells after incubation with CNCs at IC50 concentration. These findings confirm the decrease in proliferation of breast cancer cells associated with induction of apoptosis through down-regulation of the PI3K/AKT/mTOP signaling pathway. According to the provided data, the obtained CNCs are capable of inhibiting aromatase enzyme activity, which has significant implications for the treatment of cancer. Communicated by Ramaswamy H. Sarma

Phytochemical and chemotaxonomic studies on Trollius ranunculoides Hemsl.

Phytochemical study on the whole plant of Trollius ranunculoides Hemsl. led to the isolation of fifteen compounds, which could be divided into ten flavonoids (1–10), three phenolic acids (11–13) and two sterols (14–15). These isolates were elucidated based on NMR, HR-ESI-MS, UV, IR and CD data. This is the first report on chemical composition of T. ranunculoides. Compounds 1–15 were previously isolated from th genus Trollius. The chemotaxonomic significance of these isolates was also discussed.

Polyketide- and Terpenoid-Derived Metabolites Produced by a Marine-Derived Fungus, Peroneutypa sp.

Bioassay-guided investigation of the EtOAc-soluble extract of a culture of the marine-derived fungus Peroneutypa sp. M16 led to the isolation of seven new polyketide- and terpenoid-derived metabolites (1, 2, 4-8), along with known polyketides (3, 9-13). Structures of compounds 1, 2, and 4-8 were established by analysis of spectroscopic data. Absolute configurations of compounds 1, 2, 4, 6, 7, and 8 were determined by the comparison of experimental ECD spectra with calculated CD data. Compound 5 exhibited moderate antiplasmodial activity against both chloroquine-sensitive and -resistant strains of Plasmodium falciparum.

Structural and Biological Features of G-Quadruplex Aptamers as Promising Inhibitors of the STAT3 Signaling Pathway.

In this paper, we investigate the structural and biological features of G-quadruplex (G4) aptamers as promising antiproliferative compounds affecting the STAT3 signalling pathway. Targeting the STAT3 protein through high-affinity ligands to reduce its levels or activity in cancer has noteworthy therapeutic potential. T40214 (STAT) [(G3C)4] is a G4 aptamer that can influence STAT3 biological outcomes in an efficient manner in several cancer cells. To explore the effects of an extra cytidine in second position and/or of single site-specific replacements of loop residues in generating aptamers that can affect the STAT3 biochemical pathway, a series of STAT and STATB [GCG2(CG3)3C] analogues containing a thymidine residue instead of cytidines was prepared. NMR, CD, UV, and PAGE data suggested that all derivatives adopt dimeric G4 structures like that of unmodified T40214 endowed with higher thermal stability, keeping the resistance in biological environments substantially unchanged, as shown by the nuclease stability assay. The antiproliferative activity of these ODNs was tested on both human prostate (DU145) and breast (MDA-MB-231) cancer cells. All derivatives showed similar antiproliferative activities on both cell lines, revealing a marked inhibition of proliferation, particularly at 72 h at 30 µM. Transcriptomic analysis aimed to evaluate STAT's and STATB's influence on the expression of many genes in MDA-MB-231 cells, suggested their potential involvement in STAT3 pathway modulation, and thus their interference in different biological processes. These data provide new tools to affect an interesting biochemical pathway and to develop novel anticancer and anti-inflammatory drugs.

Chemical constituents with senolytic activity from the stems of Limacia scandens

While screening senotherapeutics from natural products, seven undescribed chemicals, two syringylglycerol derivatives, two cyclopeptides, one tigliane analogue, and two chromone derivatives, as well as six known compounds were isolated from the stems of Limacia scandens. The structures of compounds were elucidated through spectroscopic data analysis, including 1D and 2D NMR, HRESIMS, and CD data. All compounds were tested in replicative senescent human dermal fibroblasts (HDFs) to determine their potential as senotherapeutic agents to specifically target senescent cells. One tigliane and two chromones derivatives showed senolytic activity, indicating that senescent cells were selectively removed. Especially, 2-{2-[(3′-O-β-d-glucopyranosyl)phenyl]ethyl}chromone is expected to be a potential senotherapeutics by inducing HDF death, inhibiting the activity of senescence-associated β-galactosidase (SA-β-gal) and expressing senescence-associated secretory phenotype (SASP) factors.

Molecular interaction of lysozyme with therapeutic drug azithromycin: Effect of sodium dodecyl sulfate on binding profile

This paper describes an inclusive biophysical study elucidating the interaction of therapeutic drug azithromycin (Azith) with hen egg white lysozyme (HEWL). Spectroscopic and computational tools have been employed to study the interaction of Azith with HEWL at pH 7.4. The fluorescence quenching constant values (Ksv) exhibited a decrease with the increase in temperature which revealed the occurrence of static quenching mechanism between Azith and HEWL. The thermodynamic data demonstrated that hydrophobic interactions were predominantly involved in the Azith-HEWL interaction. The negative value of standard Gibbs free energy (ΔG°) stated that the Azith-HEWL complex formed via spontaneous molecular interactions. The effect of sodium dodecyl sulfate (SDS) surfactant monomers on the binding propensity of Azith with HEWL was insignificant at lower concentrations however the binding significantly decreased at increased concentrations of the former. Far-UV CD data revealed alteration in the secondary structure of HEWL in the presence of Azith and the overall HEWL conformation changed. Molecular docking results revealed that the binding of Azith with HEWL takes place through hydrophobic interactions and hydrogen bonds.

Chemical constituents from Microlepia hancei Prantl and their chemotaxonomic significance

A phytochemical study on the Microlepia hancei Prantl yielded sixteen compounds including five flavonol glycosides (1–5), nine pterosin sesquiterpenes (6–14), and two ent-pimarane diterpenoids (15 and 16). Their structures were elucidated based on the ORD, CD, MS, and NMR data, as well as by comparison of the published data. This is the first report on the chemical constituents of M. hancei. Among them, compounds 1–5, 7, 8, and 13 were first reported from the family Dennstaedtiaceae, and compound 14 was first reported from the genus Microlepia. Meanwhile, the chemotaxonomic significance of these compounds was discussed.

Chemical constituents from Diplopterygium chinense (Rosenstock) De Vol and their chemotaxonomic significance

A phytochemical study on the aerial parts of Diplopterygium chinense (Rosenstock) De Vol yielded fifteen compounds consisting of five steroids (1–3, 8, and 9), two diterpenoids (4 and 5), two triterpenoids (6 and 7), three flavone glycosides (10, 11, and 13), and three flavonol glycosides (12, 14, and 15). Their structures were identified according to NMR, MS, ORD, and CD data. This is the first study on the chemical constituents of D. chinense. Compounds 1–4, 6–8, 11, 12, 14, and 15 were first found from the genus Diplopterygium, while compounds 7, 11, 14, and 15 were first reported from the family Gleicheniaceae. Furthermore, the chemotaxonomic significance of these compounds was discussed.

Bisbenzylisoquinoline alkaloids from Plumula Nelumbinis inhibit vascular smooth muscle cells migration and proliferation by regulating the ORAI2/Akt pathway

Plumula Nelumbinis, the embryo of the seed of Nelumbo nucifera Gaertn, is commonly used to make tea and nutritional supplements in East Asian countries. A bioassay-guided isolation of Plumula Nelumbinis afforded six previously undescribed bisbenzylisoquinoline alkaloids, as well as seven known alkaloids. Their structures were elucidated by extensive analysis of HRESIMS, NMR, and CD data. Pycnarrhine, neferine-2α,2′β-N,N-dioxides, neferine, linsinine, isolinsinine, and nelumboferine, at 2 μM significantly suppressed the migration of MOVAS cells with inhibition ratio above 50%, more active than that of the positive control cinnamaldehyde (inhibition ratio 26.9 ± 4.92%). Additionally, neferine, linsinine, isolinsinine, and nelumboferine, were also active against the proliferation of MOVAS cells with inhibition ratio greater than 45%. The preliminary structure-activity relationships were discussed. Mechanism studies revealed that nelumboferine inhibited the migration and proliferation of MOVAS cells by regulating ORAI2/Akt signaling pathway.

Disordered-ordered protein binary classification by circular dichroism spectroscopy.

Intrinsically disordered proteins are abundant in nature and responsible for a plethora of cellular functions. They lack a stable tertiary structure and form dynamic conformational ensembles due to their characteristic physicochemical properties and amino acid composition. While numerous bioinformatics tools have been developed for in silico disorder prediction in the last decades, there is a need for experimental methods to verify the disordered state. CD spectroscopy is widely used for protein secondary structure analysis. Even without providing high-resolution information, it is especially useful when NMR, X-ray, or other techniques are problematic or one simply needs a fast technique to verify the structure of proteins. Here, we proposed an automatized binary disorder-order classification method by analyzing far-UV CD spectroscopy data. The method needs CD data at only three wavelength points, making high-throughput data collection possible. The mathematical analysis applies the k-nearest neighbor algorithm with cosine distance function, which is independent of the spectral amplitude and thus free of concentration determination errors. To reach the best classification accuracy, CD of the protein should be measurable down to 197 nm in good quality. However, the method can be used even if the spectrum can be recorded down to the wavelength of 212 nm due to the strong absorbance of the samples. The method is implemented on a webserver (https://bestsel.elte.hu/idp_classification.php) and freely available for academic users to help the experimental identification of intrinsically disordered proteins (IDPs) and the verification of the results of bioinformatics tools. This study was supported by the National Research, Development and Innovation Office of Hungary (grants 2017-1.2.1-NKP-2017-00002, PD135510, K120391, K125340, K131702, K138937 and 2019-2.1.11-TÉT-2020-00101). SRCD measurements were supported by SOLEIL (Proposals 20181890, 20191810, and 20200751).

Biological, Physical, and Atmospheric Controls on the Distribution of Cadmium and Its Isotopes in the Pacific Ocean

AbstractDespite the Pacific being the location of the earliest seawater Cd studies, the processes which control Cd distributions in this region remain incompletely understood, largely due to the sparsity of data. Here, we present dissolved Cd and δ114Cd data from the US GEOTRACES GP15 meridional transect along 152°W from the Alaskan margin to the equatorial Pacific. Our examination of this region's surface ocean Cd isotope systematics is consistent with previous observations, showing a stark disparity between northern Cd‐rich high‐nutrient low‐chlorophyll waters and Cd‐depleted waters of the subtropical and equatorial Pacific. Away from the margin, an open system model ably describes data in Cd‐depleted surface waters, but atmospheric inputs of isotopically light Cd likely play an important role in setting surface Cd isotope ratios (δ114Cd) at the lowest Cd concentrations. Below the surface, Southern Ocean processes and water mass mixing are the dominant control on Pacific Cd and δ114Cd distributions. Cd‐depleted Antarctic Intermediate Water has a far‐reaching effect on North Pacific intermediate waters as far as 47°N, contrasting with northern‐sourced Cd signatures in North Pacific Intermediate Water. Finally, we show that the previously identified negative Cd* signal at depth in the North Pacific is associated with the PO4 maximum and is thus a consequence of an integrated regeneration signal of Cd and PO4 at a slightly lower Cd:P ratio than the deep ocean ratio (0.35 mmol mol−1), rather than being related to in situ removal processes in low‐oxygen waters.

Molecular mechanism of insulin aggregation in the presence of a cationic surfactant

Protein aggregation and amyloid fibrillation are connected with neurodegenerative disorders. Insulin, a small molecular weight protein related to type II diabetes, has been shown to self-assemble to form protein aggregates. In this work, we investigated the effects of cetyltrimethylammonium bromide (CTAB) of insulin on the in vitro aggregation process at pH 7.4 and 2.0. The aggregation tendency of insulin was measured using a variety of biophysical approaches, including turbidity measurements, light scattering, far UV-CD, ThT dye binding, and transmission electron microscopy. The turbidity results demonstrated that at pH 7.4, a low concentration of CTAB (30–180 μM) causes insulin aggregation but at higer concentration (>180 μM) aggregation was not seen. However, at pH 2.0, both low as well as high concentrations of CTAB were unable to promote insulin aggregation. The ThT dye binding and far-UV CD data suggest that aggregation induced by CTAB is not having an ordered structure. Insulin treated with higher concentrations (>180 μM) of CTAB, the insulin gained a secondary structure. The possible cause of inducing aggregation in insulin is electrostatic and hydrophobic interaction because insulin contains a net negative charge at pH 7.4 and no aggregation at pH 2.0 due to electrostatic repulsion.

Solution Behavior of Bovine Skin Gelatin in the Presence of Cationic Gemini Surfactants

AbstractThe biophysical interaction between gelatin and cationic biodegradable Cm−E2O−Cm gemini surfactants (Cm represents alkyl chain where m=12, 14 and 16; E2 and O denote two ester groups and ethylene oxide, respectively) was analyzed utilizing a multi‐technique approach. The electronic absorption spectroscopy, far‐UV CD and pyrene micropolarity data evinced the formation of a complex between the concerned geminis and the biopolymer. Interestingly, the intrinsic fluorescence spectra do not exhibit concentration dependent behavior with respect to the surfactants giving an impression of poor interaction of gelatin with the geminis. Thereafter, the bulk solution properties, viz. foaming stabilities, viscosities and emulsion stabilities were measured to analyze the effect of binding. All the results combined together led to the inference of significant interaction between gelatin and the gemini surfactants which influence their physicochemical properties.

New Marine Fungal Deoxy-14,15-Dehydroisoaustamide Resensitizes Prostate Cancer Cells to Enzalutamide.

Marine fungi serve as a valuable source for new bioactive molecules bearing various biological activities. In this study, we report on the isolation of a new indole diketopiperazine alkaloid deoxy-14,15-dehydroisoaustamide (1) from the marine-derived fungus Penicillium dimorphosporum KMM 4689 associated with a soft coral. The structure of this metabolite, including its absolute configuration, was determined by HR-MS, 1D and 2D NMR as well as CD data. Compound 1 is a very first deoxyisoaustamide alkaloid possessing two double bonds in the proline ring. The isolated compound was noncytotoxic to a panel of human normal and cancer cell lines up to 100 µM. At the same time, compound 1 resensitized prostate cancer 22Rv1 cells to androgen receptor (AR) blocker enzalutamide. The mechanism of this phenomenon was identified as specific drug-induced degradation of androgen receptor transcription variant V7 (AR-V7), which also resulted in general suppression of AR signaling. Our data suggest that the isolated alkaloid is a promising candidate for combinational therapy of castration resistant prostate cancer, including drug-resistant subtypes.