1-Anilino-8-naphthalene sulfonate (ANS) is not a desirable probe for determining the molten globule state of chymopapain

Mechanisms of Air Entraining of Proteins in Cementitious Materials

While few prior studies examined the air-entraining properties of proteins in cementitious materials, the underlying mechanisms of proteins' air entraining and the interactions between proteins and cement have not been studied in the past. The significance of this article is to address this knowledge gap by investigating the effect of proteins on relevant factors that affect air entraining in cement paste and establishing an understanding of the mechanism of air entrainment with proteins. These factors include the surface tension of pore solution, protein adsorption on cement particles, cement paste hydrophobization, and flow of fresh paste. Thirteen different proteins were used to investigate the effect of a wide range of protein characteristics on air entraining. Proteins decreased the pore solution surface tension to different degrees. At low concentrations, the adsorption of proteins on cement particles slightly affected the pore solution surface tension. Protein adsorption on cement particles showed a wide range of adsorption isotherms. Proteins generally increased the flow of paste due to electrostatic repulsion between cement particles because of the adsorption of negatively charged proteins on cement particles, as well as the ball-bearing effect of bubbles in fresh paste. The surface hydrophobicity was increased in pastes with proteins. A detailed microcomputed tomography (micro-CT) analysis showed very different air void microstructures in pastes with various proteins. While a relatively strong correlation was observed between air void porosity and surface hydrophobicity, the correlation between air void porosity and the surface tension of pore solution was weak. This indicates that the accumulation of hydrophobized cement particles on the air bubble in the fresh paste, refered to as the Pickering effect, is the main mechanism of air entraining of proteins in the paste. It was shown that a high air void porosity occurs in an intermediate range of flow.

Characterization of pH-induced conformational changes in recombinant DENV NS2B-NS3pro

The increasing frequency of Dengue is a cause of severe epidemics and therefore demands strategies for effective prevention, diagnosis, and treatment. DENV-protease is being investigated as a potential therapeutic target. However, due to the flat and highly charged active site of the DENV-protease, designing orthosteric medicines is very difficult. In this study, we have done a thorough analysis of pH-dependent conformational changes in recombinantly expressed DENV protease using various spectroscopic techniques. Our spectroscopic study of DENV protease (NS2B-NS3pro) at different pH conditions gives important insights into the dynamicity of structural conformation. At physiological pH, the DENV-protease exists in a random-coiled state. Lowering the pH promotes the formation of alpha-helical and beta-sheet structures i.e. gain of secondary structure as shown by Far-UV CD. The light scattering and Thioflavin T (ThT)-binding assay proved the aggregation-prone tendency of DENV-protease at pH 4.0. Further, the confocal microscopy image intensity showed the amorphous aggregate formation of DENV protease at pH 4.0. Thus, the DENV protease acquires different conformations with changes in pH conditions. Together, these results have the potential to facilitate the design of a conformation destabilizer-based therapeutic strategy for dengue fever.

Unraveling the unexpected aggregation behavior of Pyrazole-Based compounds Targeting Mycobacterium tuberculosis UDP-Galactopyranose mutase

A pyrazole-based compound, MS208, was previously identified as an inhibitor of UDP-Galactopyranose Mutase from Mycobacterium tuberculosis (MtUGM). Targeting this enzyme is a novel therapeutic strategy for the development of new antituberculosis agents because MtUGM is an essential enzyme for the bacterial cell wall synthesis and it is not present in human. It was proposed that MS208 targets an allosteric site in MtUGM as MS208 followed a mixed inhibition model. DA10, an MS208 analogue, showed competitive inhibition rather than mixed inhibition. In this paper, we have used an integrated biophysical approach, including thermal shift assays, dynamic light scattering and nuclear magnetic resonance experiments, to show that MS208 and many analogues displayed unexpected aggregation behavior against MtUGM.

Impacts of Halogen Substitutions on Bisphenol A Compounds Interaction with Human Serum Albumin: Exploring from Spectroscopic Techniques and Computer Simulations

Bisphenol A (BPA) is an endocrine-disrupting compound, and the binding mechanism of BPA with carrier proteins has drawn widespread attention. Halogen substitutions can significantly impact the properties of BPA, resulting in various effects for human health. Here, we selected tetrabromobisphenol A (TBBPA) and tetrachlorobisphenol A (TCBPA) to investigate the interaction between different halogen-substituted BPAs and human serum albumin (HSA). TBBPA/TCBPA spontaneously occupied site I and formed stable binary complexes with HSA. Compared to TCBPA, TBBPA has higher binding affinity to HSA. The effect of different halogen substituents on the negatively charged surface area of BPA was an important reason for the higher binding affinity of TBBPA to HSA compared to TCBPA. Hydrogen bonds and van der Waals forces were crucial in the TCBPA-HSA complex, while the main driving factor for the formation of the TBBPA-HSA complex was hydrophobic interactions. Moreover, the presence of TBBPA/TCBPA changed the secondary structure of HSA. Amino acid residues such as Lys199, Lys195, Phe211, Arg218, His242, Leu481, and Trp214 were found to play crucial roles in the binding process between BPA compounds and HSA. Furthermore, the presence of halogen substituents facilitated the binding of BPA compounds with HSA.

Role of charged residues of the "electrostatic loop" of hSOD1 in promotion of aggregation: Implications for the mechanism of ALS-associated mutations under amyloidogenic conditions

Protein misfolding and amyloid formation are hallmarks of numerous diseases, including amyotrophic lateral sclerosis (ALS), in which hSOD1 aggregation is involved in pathogenesis. We used two point mutations in the electrostatic loop, G138E and T137R, to analyze charge distribution under destabilizing circumstances to gain more about how ALS-linked mutations affect SOD1 protein stability or net repulsive charge. We show that protein charge is important in the ALS disease process using bioinformatics and experiments. The MD simulation findings demonstrate that the mutant protein differs significantly from WT SOD1, which is consistent with the experimental evidence. The specific activity of the wild type was 1.61 and 1.48 times higher than that of the G138E and T137R mutants, respectively. Under amyloid induction conditions, the intensity of intrinsic and ANS fluorescence in both mutants reduced. Increasing the content of β-sheet structures in mutants can be attributed to aggregation propensity, which was confirmed using CD polarimetry and FTIR spectroscopy. Our findings show that two ALS-related mutations promote the formation of amyloid-like aggregates at near physiological pH under destabilizing conditions, which were detected using spectroscopic probes such as Congo red and ThT fluorescence, and also further confirmation of amyloid-like species by TEM. Overall, our results provide evidence supporting the notion that negative charge changes combined with other destabilizing factors play an important role in increasing protein aggregation by reducing repulsive negative charges.

Insights into the remarkable attenuation of hen egg white lysozyme amyloid fibril formation mediated by biogenic gold nanoparticles stabilized by quercetin-functionalized tara gum

Aberrant protein misfolding and/or aggregation and fibrillation has been linked to the pathogenesis of several debilitating chronic diseases including Alzheimer's and Parkinson's disease. Inhibiting protein amyloidogenesis has been proposed as a viable strategy to prevent or ameliorate associated disorders. Herein, we investigated the anti-amyloidogenic properties of biogenic gold nanoparticles (QTG-GNP) prepared via a simple green chemistry route and stabilized by quercetin-functionalized tara gum (QTG). The synthesized QTG-GNP was extensively characterized for its physicochemical attributes via UV-visible spectroscopy, TEM, FESEM, EDX, DLS/Zeta potential, FTIR, RAMAN, XRD, XPS, and TGA analyses, as well as for its biological properties. The results revealed that small-sized (5.01 ± 1.17 nm), well-dispersed, highly stable and round-shaped biogenic gold nanoparticles were successfully synthesized at room temperature with QTG as the sole reductant /stabilizer. Importantly, QTG-GNP demonstrated potent anti-aggregation and fibrillation inhibitory effects against amyloidogenic hen egg white lysozyme (HEWL). Also, QTG-GNP was able to dissociate pre-formed HEWL amyloid fibrils. Furthermore, the constructed nanoparticles exhibited potent anti-radical activities against DPPH and ABTS⁺ and were cytocompatible with mouse L929 fibroblast cells. On the basis of these findings, it was established that QTG-GNP holds strong prospects for further development as an agent for countering protein aggregation and associated disease conditions.

Formation of Protamine and Zn-Insulin Assembly: Exploring Biophysical Consequences

The insulin-protamine interaction is at the core of the mode of action in many insulin formulations (Zn + insulin + protamine) and to treat diabetes, in which protamine is added to the stable form of hexameric insulin (Zn-insulin). However, due to the unavailability of quantitative data and a high-resolution structure, the binding mechanism of the insulin-protamine complex remains unknown. In this study, it was observed that Zn-insulin experiences destabilization as observed by the loss of secondary structure in circular dichroism (CD), and reduction in thermal stability in melting study, upon protamine binding. In isothermal titration calorimetry (ITC), it was found that the interactions were mostly enthalpically driven. This is in line with the positive ΔC _m value (+880 cal mol^-1), indicating the role of hydrophilic interactions in the complex formation, with the exposure of hydrophobic residues to the solvent, which was firmly supported by the 8-anilino-1-naphthalene sulfonate (ANS) binding study. The stoichiometry (N) value in ITC suggests the multiple insulin molecules binding to the protamine chain, which is consistent with the picture of the condensation of insulin in the presence of protamine. Atomic force microscopy (AFM) suggested the formation of a heterogeneous Zn-insulin-protamine complex. In fluorescence, Zn-insulin experiences strong Tyr quenching, suggesting that the location of the protamine-binding site is near Tyr, which is also supported by the molecular docking study. Since Tyr is critical in the stabilization of insulin self-assembly, its interaction with protamine may impair insulin's self-association ability and thermodynamic stability while at the same time promoting its flexible conformation desired for better biological activity.

An insight into the interaction between Indisulam and human serum albumin: Spectroscopic method, computer simulation and in vitro cytotoxicity assay

Indisulam (IDM) is a sulfanilamide anticancer agent and has been identified as a molecular glue recently. It shows potential for novel therapies development and brings more hope for curing human diseases. The affinity between molecular glues and plasma protein makes it significant to understand the characteristics of such substances. Therefore, the interaction between IDM and human serum albumin (HSA) was explored through solvent experiments, computer simulation experiments, enzyme kinetics experiments, and cell viability assay. The results revealed that IDM and HSA spontaneously formed stable binary complex with the binding constant of the order 10⁵ M^-1. IDM inserted in the site I of HSA, resulting the change in HSA secondary structure. And π electrons in IDM's benzene rings, as well as van der Waals forces and the H-bond, all helped to stabilize the HSA-IDM complex. The results of molecular dynamic simulation (MD) corresponded with the results from solvent experiment well. For instance, there were approximately 1-5 H-bonds between IDM and HSA. Lys199 and Arg218 were crucial energy contributors in the binding process. The esterase-like activity experiment confirmed that IDM inhibited the catalytic activity of HSA. In addition, cell experiment revealed that serum albumin can significantly reduce the cytotoxicity of IDM towards human embryonic kidney 293T (HEK293T) cells.

Mechanistic In Vitro Dissection of the Inhibition of Amyloid Fibrillation by n-Acetylneuraminic Acid: Plausible Implication in Therapeutics for Neurodegenerative Disorders

A variety of neurodegenerative disorders including Parkinson's disease are due to fibrillation in amyloidogenic proteins. The development of therapeutics for these disorders is a topic of extensive research as effective treatments are still unavailable. The present study establishes that n-acetylneuraminic acid (Neu5ac) inhibits the amyloid fibrillation of hen egg-white lysozyme (HEWL) and α-synuclein (SYN), as observed using various biophysical techniques and cellular assays. Neu5ac inhibits the amyloid formation in both proteins, as suggested from the reduction in the ThT fluorescence and remnant structures in transmission electron microscopy micrographs observed in its presence. In HEWL fibrillation, Neu5ac decreases the hydrophobicity and resists the transition of the α-helix to a β-sheet, as observed by an ANS binding assay, circular dichroism (CD) spectra, and Fourier transform infrared measurements, respectively. Neu5ac stabilizes the states that facilitate the amyloid formation in HEWL and SYN, as demonstrated by an enhanced intrinsic fluorescence in its presence, which is further confirmed by an increase in T_m obtained from differential scanning calorimetry thermograms and an increase in the near-UV CD signal for HEWL with Neu5ac. However, the increase in stability is not a manifestation of Neu5ac binding to amyloid facilitating (partially folded or native) states of both proteins, as verified by isothermal titration calorimetry and fluorescence binding measurements. Besides, Neu5ac also attenuates the cytotoxicity of amyloid fibrils, as evaluated by a cell toxicity assay. These findings provide mechanistic insights into the Neu5ac action against amyloid fibrillation and may establish it as a plausible inhibitor molecule against neurodegenerative disorders.

Phytochemical thymoquinone prevents hemoglobin glycoxidation and protofibrils formation: A biophysical aspect

d-ribose, a reducing sugar, in diabetic hyperglycemia provokes non-enzymatic glycoxidation of hemoglobin (Hb), an abundant protein of red blood cells (RBCs). Different types of intermediates adduct formation occur during glycoxidation, such as advanced glycation end-products (AGEs) which lead to amyloid formation due to structural and conformational alterations in protein. Therefore, the study of these intermediate adducts plays a pivotal role to discern their relationship with diabetes mellitus and related disorders. Here, we investigated the interaction mechanism of d-ribose with Hb, and Hb prebound phytochemical thymoquinone (TQ). Our investigation reveals that the interaction of TQ with histidine residues of Hb interferes with the interaction of d-ribose with glycine residues at the glycation-site. Based on that, we had performed a time-based (21-days) in-vitro glycoxidation study at 37 °C to investigate the structural perturbation mechanism of Hb at different time-intervals in absence/presence of TQ. We found that prolonged glycoxidation induces amyloid formation in absence of TQ but in its presence, the process was prohibited. In summary, this study examined and characterized biophysically different intermediate-states of protein carrying glycoxidation-modification. Our findings suggested that TQ potentially affects interaction of d-ribose with Hb that prevents glycoxidation and protofibril formation, which establishes TQ as a potential therapeutic agent.

Characterization of Conjugates between α-Lactalbumin and Benzyl Isothiocyanate-Effects on Molecular Structure and Proteolytic Stability

In complex foods, bioactive secondary plant metabolites (SPM) can bind to food proteins. Especially when being covalently bound, such modifications can alter the structure and, thus, the functional and biological properties of the proteins. Additionally, the bioactivity of the SPM can be affected as well. Consequently, knowledge of the influence of chemical modifications on these properties is particularly important for food processing, food safety, and nutritional physiology. As a model, the molecular structure of conjugates between the bioactive metabolite benzyl isothiocyanate (BITC, a hydrolysis product of the glucosinolate glucotropaeolin) and the whey protein α-lactalbumin (α-LA) was investigated using circular dichroism spectroscopy, anilino-1-naphthalenesulfonic acid fluorescence, and dynamic light scattering. Free amino groups were determined before and after the BITC conjugation. Finally, mass spectrometric analysis of the BITC-α-LA protein hydrolysates was performed. As a result of the chemical modifications, a change in the secondary structure of α-LA and an increase in surface hydrophobicity and hydrodynamic radii were documented. BITC modification at the ε-amino group of certain lysine side chains inhibited tryptic hydrolysis. Furthermore, two BITC-modified amino acids were identified, located at two lysine side chains (K32 and K113) in the amino acid sequence of α-LA.

Cancer microcell initiation and determination

BACKGROUND

Cancer remains one of the leading causes of death worldwide, despite the possibilities to detect early onset of the most common cancer types. The search for the optimal therapy is complicated by the cancer diversity within tumors and the unsynchronized development of cancerous cells. Therefore, it is necessary to characterize cancer cell populations after treatment has been applied, because cancer recurrence is not rare. In our research, we concentrated on small cancer cell subpopulation (microcells) that has a potential to be cancer resistance source. Previously made experiments has shown that these cells in small numbers form in specific circumstances after anticancer treatment.

METHODS

In experiments described in this research, the anticancer agents' paclitaxel and doxorubicin were used to stimulate the induction of microcells in fibroblast, cervix adenocarcinoma, and melanoma cell lines. Mainly for the formation of microcells in melanoma cells. The drug-stimulated cells were then characterized in terms of their formation efficiency, morphology, and metabolic activity.

RESULTS

We observed the development of cancer microcells and green fluorescent protein (GFP) transfection efficiency after stress. In the time-lapse experiment, we observed microcell formation through a renewal process and GFP expression in the microcells. Additionally, the microcells were viable after anticancer treatment, as indicated by the nicotinamide adenine dinucleotide hydrogen phosphate (NADPH) enzyme activity assay results. Taken together, these findings indicate that cancer microcells are viable and capable of resisting the stress induced by anticancer drugs, and these cells are prone to chemical substance uptake from the environment.

CONCLUSION

Microcells are not only common to a specific cancer type, but can be found in any tumor type. This study could help to understand cancer emergence and recurrence. The appearance of microcells in the studied cancer cell population could be an indicator of the individual anticancer therapy effectiveness and patient survival.

Nanoclay based study on protein stability and aggregation and its implication in human health

Protein aggregation is the major cause of several acute amyloid diseases such as Parkinson's, Huntington's, Alzheimer's, Lysozyme Systemic amyloidosis, Diabetes-II etc. While these diseases have attracted much attention but the cure is still unavailable. In the present study, Human Serum Albumin (HSA) and Human Lysozyme (HL) were used as the model proteins to investigate their aggregations. Nanoclays are hydrous silicates found in clay fraction of soil and known as natural nanomaterials. They have long been used in several applications in health-related products. In the present paper, the different types of nanoclays (MMT K-10, MMT K-30, Halloysite, Bentonite) were used to inhibit the process of HSA and HL aggregation. Aggregation experiments were evaluated using several biophysical tools such as Turbidity measurements, Intrinsic fluorescence, 1-anilino-8-naphthalene sulfonate (ANS), Thioflavin T (Th T), congo red (CR) binding assays and Circular dichroism. Results demonstrated that all the nanoclays inhibit the DTT-induced aggregation. However, bentonite and MMT K-10 were progressively intense and potent as they slowed down nucleation stage which can be perceived using several biophysical techniques. Hence, nanoclays can be used as an artificial chaperone and might provide effective treatment against several protein aggregation related disorders.

pH and alcohol induced structural transition in Ntf2 a nuclear transport factor of Saccharomyces cerevisiae

Ntf2 is a nuclear envelope protein, which play a pivotal role in nucleocytoplasmic transport and mediates the nuclear import of RanGDP. It interacts with various nucleoporins along with Ran-GDP and part of a multicomponent system that assembles at the nuclear pore complex (NCP) during nuclear import. Here, we have described the biophysical characterization of Ntf2 from Saccharomyces cerevisiae. Recombinant Ntf2 showed increment in the β-sheet content as well as decrement in the α-helix content from pH-7.0 to pH-4.0. A subsequent decrease in the pH led to increment in the α-helical content along with decrement in β-sheet content. Intrinsic fluorescence studies demonstrated the unfolding of the protein below physiological pH. Ntf2 showed stabilization as well as phenomenal phase transition (β sheet to α helix) by increase in alcohol concentration from 10% to 70%. Further increase in alcohol concentration (90%) resulted in residual secondary structure in Ntf2 protein. Presence of ammonium sulfate also stabilizes the secondary structure of Ntf2 protein. The structural characterization reveals the flexibility and the stability of Ntf2 at various conditions. These structural alterations in Ntf2 protein probably occurs in the course of nucleocytoplasmic transport when it interacts with other proteins moving towards its final destination.

An insight into structural plasticity and conformational transitions of transcriptional co-activator Sus1

RNA biogenesis and mRNA transport are an intricate process for every eukaryotic cell. SAGA, a transcriptional coactivator and TREX-2 are the two major complexes participate in this process. Sus1 is a transcription export factor and part of both the SAGA and the TREX-2 complex. The competitive exchange of Sus1 molecule between SAGA and TREX-2 complex modulates their function which is credited to structural plasticity of Sus1. Here, we portray the biophysical characterization of Sus1 from S. cerevisiae. The recombinant Sus1 is a α-helical structure which is stable at various pH conditions. We reported the α-helix to β-sheet transition at the low pH as well as at high pH. Sus1 showed 50% reduction in the fluorescence intensity at pH-2 as compared to native protein. The fluorescence studies demonstrated the unfolding of tertiary structure of the protein with variation in pH as compared to neutral pH. The same results were obtained in the ANS binding and acrylamide quenching studies. Similarly, the secondary structure of the Sus1 was found to be stable till 55% alcohol concentration while tertiary structure was stable up to 20% alcohol concentration. Further increase in the alcohol concentration destabilizes the secondary as well as tertiary structure. The 300 mM concentration of ammonium sulfate also stabilizes the secondary structure of the protein. The structural characterization of this protein is expected to unfold the process of the transportation of the mRNA with cooperation of different proteins.

Effect of pH on the structure and function of pyruvate dehydrogenase kinase 3: Combined spectroscopic and MD simulation studies

Pyruvate dehydrogenase kinase-3 (PDK3) plays important role in the glucose metabolism and is associated with cancer progression, and thus being considered as an attractive target for cancer therapy. In this study, we employed spectroscopic techniques to study the structural and conformational changes in the PDK3 at varying pH conditions ranging from pH 2.0 to 12.0. UV/Vis, fluorescence and circular dichroism spectroscopic measurements revealed that PDK3 maintains its native-like structure (both secondary and tertiary) in the alkaline conditions (pH 7.0-12.0). However, a significant loss in the structure was observed under acidic conditions (pH 2.0-6.0). The propensity of aggregate formation at pH 4.0 was estimated by thioflavin T fluorescence measurements. To further complement structural data, kinase activity assay was performed, and maximum activity of PDK3 was observed at pH 7.0-8.0 range; whereas, its activity was lost under acidic pH. To further see conformational changes at atomistic level we have performed all-atom molecular dynamics at different pH conditions for 150 ns. A well defined correlation was observed between experimental and computational studies. This work highlights the significance of structural dependence of pH for wide implications in protein-protein interaction, biological function and drug design procedures.

Cerium oxide NPs mitigate the amyloid formation of α-synuclein and associated cytotoxicity

Aim

Among therapeutic proposals for amyloid-associated disorders, special attention has been given to the exploitation of nanoparticles (NPs) as promising agents against aggregation.

Methods

In this paper, the inhibitory effect of cerium oxide (CeO₂) NPs against α-synuclein (α-syn) amyloid formation was explored by different methods such as Thioflavin T (ThT) and 8-anilinonaphthalene-1-sulfonic acid (ANS) fluorescence spectroscopy, Congo red adsorption assay, circular dichroism (CD) spectroscopy, transmission electron microscopy (TEM), and bioinformatical approaches. Also, the cytotoxicity of α-syn amyloid either alone or with CeO₂ NPs against neuron-like cells (SH-SY5Y) was examined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), flow cytometry, and quantitative real-time polymerase chain reaction (Bax and Bcl-2 gene expression) assays.

Results

ThT and ANS fluorescence assays indicated that CeO₂ NPs inhibit the formation of aggregated species and hydrophobic patches of α-syn in amyloidogenic conditions, respectively. Congo red and CD assays demonstrated that CeO₂ NPs reduce the formation of amyloid species and β-sheets structures of α-syn molecules, respectively. TEM investigation also confirmed that CeO₂ NPs limited the formation of well-defined fibrillary structures of α-syn molecules. Molecular docking and dynamic studies revealed that CeO₂ NPs could bind with different affinities to α-syn monomer and amyloid species and fibrillar structure of α-syn is disaggregated in the presence of CeO₂ NPs. Moreover, cellular assays depicted that CeO₂ NPs mitigate the cell mortality, apoptosis, and the ratio of Bax/Bcl-2 gene expression associated with α-syn amyloids.

Conclusion

It may be concluded that CeO₂ NPs can be used as therapeutic agents to reduce the aggregation of proteins and mitigate the occurrence of neurodegenerative diseases.

A spectroscopic study of a cyclodextrin-based polymer and the “molecular accordion” effect

The formation of host–guest complexes was studied for two hosts: β-cyclodextrin (β-CD) and a cross-linked polymer containing an equimolar ratio of β-CD and hexamethylene diisocyanate (HDI), denoted as HDI-1. The thermodynamics of host–guest binding were studied with 1-anilinonaphthalene-8-sulfonic acid (1,8-ANS) using steady-state fluorescence spectroscopy in aqueous solution at variable temperature and ambient pH. The association of 1,8-ANS with β-CD and HDI-1 showed a fluorescence enhancement of ∼4 and 12 units, respectively. Greater fluorescence enhancement for the polymer/dye system indicates the presence of multiple binding sites (inclusion and interstitial). By contrast, the β-CD/dye system adopts trends that indicate the formation of well-defined inclusion complexes. HDI-1 has inclusion sites (β-CD) and interstitial domains (HDI) that afford dual binding with variable binding affinity. Simplified binding models employed herein address the role of inclusion binding without an explicit account for higher order or secondary binding equilibria. The approximate 1:1 binding constant (K1:1) for CD/1,8-ANS is about two-fold greater over the HDI-1/1,8-ANS system. HDI-1 displays cooperative effects among the polymer subunits, according to changes in relative fluorescence intensity due to structural transitions and binding site loci. The relative fluorescence intensities of the HDI-1/1,8-ANS system relate to a reversible temperature-driven structural transition (globular ⇌ extended) of the polymer between 5 °C and 60 °C, in contrast to the β-CD/1,8-ANS complex. The temperature- and guest-driven structural transition, described as the “molecular accordion” effect, is supported by new insight provided by complementary fluorescence and 1H NMR spectral results in aqueous solution.

New insight on 8-anilino-1-naphthalene sulfonic acid interaction with TgFNR for hydrophobic exposure analysis

The exposed hydrophobic patches of protein are widely detected through the binding by the fluorescent probes such as 1-anilino-8-naphthalene sulfonate (ANS), Nile Red (NR) and 1-(N-phenylamino) naphthalene, N-(1-Naphthyl) aniline (1NPN). Interestingly, at pH4, where the Toxoplasma gondii Ferredoxin-NADP(+) reductase (TgFNR) is stable, an exclusive binding and fluorescence emission was observed for ANS. To understand the underlying difference in the binding of ANS, NR and 1NPN; their effect on the protein structure was studied in detail. ANS was found to interact with TgFNR via electrostatic as well as hydrophobic interactions at pH4. NR and 1NPN did not show any such binding to TgFNR in the similar conditions, however showed strong hydrophobic interaction in the presence of NaCl or DSS (2, 2-dimethyl-2-silapentane-5-sulfonate). The subsequent structural studies suggest that ANS, NaCl and DSS induced partial unfolding of TgFNR by modulating ionic interactions of the enzyme, leading to the exposure of buried hydrophobic patches amicable for the binding by NR and 1NPN. The induced unfolding of TgFNR by ANS is unique and thus cautions to use the fluorescent dye as simple indicator to probe the exposed hydrophobic patches of the protein or its folding intermediates.

Photoacids as a new fluorescence tool for tracking structural transitions of proteins: following the concentration-induced transition of bovine serum albumin

Spectroscopy-based techniques for assessing structural transitions of proteins follow either an intramolecular chromophore, as in absorption-based circular dichroism (CD) or fluorescence-based tryptophan emission, or an intermolecular chromophore such as fluorescent probes. Here a new fluorescent probe method to probe the structural transition of proteins by photoacids is presented, which has a fundamentally different photo-physical origin to that of common fluorescent probes. Photoacids are molecules that release a proton upon photo-excitation. By following the steady-state and time-resolved emission of the protonated and de-protonated species of the photoacid we probe the environment of its binding site in bovine serum albumin (BSA) in a wide range of weight concentrations (0.001-8%). We found a unique concentration-induced structural transition of BSA at pH2 and at concentrations of >0.75%, which involves the exposure of its hydrophobic core to the solution. We confirm our results with the common tryptophan emission method, and show that the use of photoacids can result in a much more sensitive tool. We also show that common fluorescent probes and the CD methodologies have fundamental restrictions that limit their use in a concentration-dependent study. The use of photoacids is facile and requires only a fluorospectrometer (and preferably, but not mandatorily, a time-resolution emission system). The photoacid can be either non-covalently (as in this study) or covalently attached to the molecule, and can be readily employed to follow the local environment of numerous (bio-)systems.

DNA induced aggregation of stem bromelain; a mechanistic insight

Negatively charged species such as nucleic acids have commonly been found to be associated with the proteinaceous deposits in the tissues of patients with amyloid diseases.

Rosin Surfactant QRMAE Can Be Utilized as an Amorphous Aggregate Inducer: A Case Study of Mammalian Serum Albumin

Quaternary amine of diethylaminoethyl rosin ester (QRMAE), chemically synthesized biocompatible rosin based cationic surfactant, has various biological applications including its use as a food product additive. In this study, we examined the amorphous aggregation behavior of mammalian serum albumins at pH 7.5, i.e., two units above their isoelectric points (pI ~5.5), and the roles played by positive charge and hydrophobicity of exogenously added rosin surfactant QRMAE. The study was carried out on five mammalian serum albumins, using various spectroscopic methods, dye binding assay, circular dichroism and electron microscopy. The thermodynamics of the binding of mammalian serum albumins to cationic rosin modified surfactant were established using isothermal titration calorimetry (ITC). It was observed that a suitable molar ratio of protein to QRMAE surfactant enthusiastically induces amorphous aggregate formation at a pH above two units of pI. Rosin surfactant QRMAE-albumins interactions revealed a unique interplay between the initial electrostatic and the subsequent hydrophobic interactions that play an important role towards the formation of hydrophobic interactions-driven amorphous aggregate. Amorphous aggregation of proteins is associated with varying diseases, from the formation of protein wine haze to the expansion of the eye lenses in cataract, during the expression and purification of recombinant proteins. This study can be used for the design of novel biomolecules or drugs with the ability to neutralize factor(s) responsible for the aggregate formation, in addition to various other industrial applications.