Cooperative α-helix formation of β-lactoglobulin induced by sodium n-alkyl sulfates

Interfacial Interactions between Nanoplastics and Biological Systems: toward an Atomic and Molecular Understanding of Plastics-Driven Biological Dyshomeostasis

Micro- and nano-plastics (NPs) are found in human milk, blood, tissues, and organs and associate with aberrant health outcomes including inflammation, genotoxicity, developmental disorders, onset of chronic diseases, and autoimmune disorders. Yet, interfacial interactions between plastics and biomolecular systems remain underexplored. Here, we have examined experimentally, in vitro, in vivo, and by computation, the impact of polystyrene (PS) NPs on a host of biomolecular systems and assemblies. Our results reveal that PS NPs essentially abolished the helix-content of the milk protein β-lactoglobulin (BLG) in a dose-dependent manner. Helix loss is corelated with the near stoichiometric formation of β-sheet elements in the protein. Structural alterations in BLG are also likely responsible for the nanoparticle-dependent attrition in binding affinity and weaker on-rate constant of retinol, its physiological ligand (compromising its nutritional role). PS NP-driven helix-to-sheet conversion was also observed in the amyloid-forming trajectory of hen egg-white lysozyme (accelerated fibril formation and reduced helical content in fibrils). Caenorhabditis elegans exposed to PS NPs exhibited a decrease in the fluorescence of green fluorescent protein-tagged dopaminergic neurons and locomotory deficits (akin to the neurotoxin paraquat exposure). Finally, in silico analyses revealed that the most favorable PS/BLG docking score and binding energies corresponded to a pose near the hydrophobic ligand binding pocket (calyx) of the protein where the NP fragment was found to make nonpolar contacts with side-chain residues via the hydrophobic effect and van der Waals forces, compromising side chain/retinol contacts. Binding energetics indicate that PS/BLG interactions destabilize the binding of retinol to the protein and can potentially displace retinol from the calyx region of BLG, thereby impairing its biological function. Collectively, the experimental and high-resolution in silico data provide new insights into the mechanism(s) by which PS NPs corrupt the bimolecular structure and function, induce amyloidosis and onset neuronal injury, and drive aberrant physiological and behavioral outcomes.

An Atomic and Molecular Insight into How PFOA Reduces α-Helicity, Compromises Substrate Binding, and Creates Binding Pockets in a Model Globular Protein

Per- and polyfluoroalkyl substances (PFAS) pose significant health risks due to their widespread presence in various environmental and biological matrices. However, the molecular-level mechanisms underlying the interactions between PFAS and biological constituents, including proteins, carbohydrates, lipids, and DNA, remain poorly understood. Here, we investigate the interactions between a legacy PFAS, viz. perfluorooctanoic acid (PFOA), and the milk protein β-lactoglobulin (BLG) obtained using a combination of experimental and computational techniques. Circular dichroism studies reveal that PFOA perturbs the secondary structure of BLG, by driving a dose-dependent loss of α-helicity and alterations in its β-sheet content. Furthermore, exposure of the protein to PFOA attenuates the on-rate constant for the binding of the hydrophobic probe 8-anilino-1-naphthalene sulfonic acid (ANS), suggesting potential functional impairment of BLG by PFOA. Steered molecular dynamics and umbrella sampling calculations reveal that PFOA binding leads to the formation of an energetically favorable novel binding pocket within the protein, when residues 129-142 are steered to unfold from their initial α-helical structure, wherein a host of intermolecular interactions between PFOA and BLG's residues serve to insert the PFOA into the region between the unfolded helix and beta-sheets. Together, the data provide a novel understanding of the atomic and molecular mechanism(s) by which PFAS modulates structure and function in a globular protein, leading to a beginning of our understanding of altered biological outcomes.

The influence of KCl concentration on the gelation of myofibrillar protein giant squid (Dosidicus gigas) due to molecular conformation change

Introduction

Protein gelation process is of importance in food industry. The objective of this study is to investigate the influence of salt concentration variation, which induced protein conformation change, on protein's intermolecular interactions and its gelation process.

Methods

Paramyosin has been separated and purified from myofibrillar protein extracted from giant squid. Then Giant squid's paramyosin molecular mass and intermolecular interactions were quantified by means of light scattering techniques. Finally, the micro-rheology study via diffusing wave spectroscopy (DWS) technique revealed that this conformation change dramatically affected myofibrillar protein gelation process.

Results

The obtained apparent molecular weight (ca 2 × 10⁵ g/mol) suggested that protein molecules existed as dimers, while the second virial coefficient A2 significantly reduced from -3.98456 × 10^-5 to -5.07575 × 10^-4 ml mol/g² when KCl concentrated from 0.15 to 1 mol/L. Light scattering data also suggest that paramyosin dimers are stiff, with a persistence length of 120 nm, almost the length of a molecule and independent of salt concentration. Mean-square displacement (MSD) of tracer particles at 5 temperatures with 4 salt concentrations displayed that this conformation change had dramatic effect. Therefore, G' and G" were remarkably altered with at least one order of magnitude difference owing to this event occurrence.

Conclusions

Paramyosin conformation change due to KCl concentrated enhances attractive interactions with apparent molecular mass increase, which resulted in majority paramyosin molecules (> 99%) in dimeric form and promoted aggregates formation. DWS technique revealed that the conformation change dramatic affected this process characterized by the correlation functions, MSD, and G' and G". This study brings forward data on understanding the effect of a major salt supplement, KCl, on the chemical physics of a major muscle protein.

The Molecular Mechanism of Traditional Chinese Medicine Prescription: Gu-tong Formula in Relieving Osteolytic Bone Destruction

Bone metastasis is a common complication in patients with advanced tumors, causing pain and bone destruction and affecting their quality of life. Typically, complementary and alternative medicine (CAM), with unique theoretical guidance, has played key roles in the treatment of tumor-related diseases. Gu-tong formula (GTF), as a representative prescription of traditional Chinese medicine, has been demonstrated to be an effective clinical medication for the relief of cancer pain. However, the molecular mechanism of GTF in the treatment of osteolytic metastasis is still unclear. Herein, we employ network pharmacology and molecular dynamics methods to uncover the potential treatment mechanism, indicating that GTF can reduce the levels of serum IL6 and TGFB1 and thus limit the scope of bone cortical damage. Among the active compounds, sesamin and deltoin can bind stably with IL6 and TGFB1, respectively, and have the potential to become anti-inflammatory and anticancer drugs. Although the reasons for the therapeutic effect of GTF are complex and comprehensive, this work provides biological plausibility in the treatment of osteolytic metastases, which has a guiding significance for the treatment of cancer pain with CAM.

Molecular insights into the crystalline nanocellulose and human lysozyme interactions: An experimental and theoretical research

In the present research, we performed a combination of detailed computational and spectroscopic methods to determine the effect of crystalline nanocellulose (CNC) on the structure and dynamics of human lysozyme (hLyz). Fluorescence spectroscopy revealed static quenching as the major mechanism in forming a stable CNC-hLyz complex, and the binding was energetically favorable. The obtained values of the thermodynamic parameters (∆G, ∆H, and ∆S) proposed that the complex formation between the enzyme and cellulose nanocrystals is driven by electrostatic interactions, which were also confirmed by molecular dynamics (MD) simulation. Additionally, the MD simulation analysis displays that the enzyme's structural elements and tertiary structure were primarily maintained, and only loops regions were affected in the presence of cellulose nanocrystals. At the same time, circular dichroism (CD) outcomes highlighted that higher cellulose nanocrystals concentration caused a reduction in the secondary structure of hLyz. Our observations proved that low cellulose nanocrystals concentrations have no considerable effect on the human lysozyme structure. The current research results provide a valuable opportunity to elucidate the molecular interactions between protein and nanocelluloses, guiding further investigations of CNC-based material for biomedical, pharmaceutical, and food industry applications.

Classification of protein solubilizing additives by fluorescence assay

Aromatic interaction plays a crucial role in controlling protein interaction by additives. Here we investigated the interaction of protein salting-in (solubilizing) additives with tryptophan (Trp), tyrosine (Tyr), indole, and proteins based on their fluorescence spectra. Five salting-in additives, i.e., arginine (Arg), urea, guanidine (Gdn), ethylene glycol (EG), and magnesium chloride (MgCl₂), showed different effects on the fluorescence properties of Trp and Tyr. Arg significantly reduced fluorescence intensity of Trp and Tyr, as was the case for glycine to a lesser extent. MgCl₂ and calcium chloride (CaCl₂) showed little effect on the aromatic fluorescence spectra. Gdn also showed little effect on the aromatic fluorescence spectra of Trp and Tyr even at high concentrations. EG increased the aromatic fluorescence intensity of Trp and Tyr with blue-shifted emission wavelength. Urea enhanced fluorescence of Trp and Tyr without altering emission wavelength. These results indicate that the protein solubilizing additives interact with aromatic groups differently.

Spectroscopic studies of simultaneous binding of cyclophosphamide and imatinib mesylate to human holo-transferrin

The interactions of proteins with drugs are very important from a pharmacological point of view. Holo-transferrin is a blood-plasma glycoprotein whose main function is iron-binding and the transport of other ligands. Additionally, the protein is only transferrin-form recognized by TfR1 and TfR2 receptors at the surface of rapidly proliferating malignant cells. Imatinib mesylate is a tyrosine-kinase inhibitor mainly used in the treatment of blood cancers, frequently in multidrug therapy with cyclophosphamide. In this study the effect of cyclophosphamide on the interaction of imatinib mesylate with human holo-transferrin has been investigated. Using spectroscopic techniques such as fluorescence, circular dichroism, ultraviolet-visible and electrophoretic light scattering additive parameters, system stability and the effect of the ligands on the protein conformation at varying pH values have been defined. Calculated quenching constants are in the order of 2 × 10⁴ M^-1 and the type of interaction depends on the reaction medium. Under physiological conditions binding constant is 1.329 × 10⁶ M^-1 whereas in an environment similar to that of cancer cells the constant is significantly lower, K_a = 6.060 × 10⁴ M^-1. N values are approximate to 1 in all cases. Moreover, some changes are observed in the α-helical structure of the protein after interaction with the drugs and the presence of cyclophosphamide slightly stabilizes the protein secondary structure. All collected data proves the effect of cyclophosphamide on the interaction between imatinib mesylate and human holo-transferrin. It is of great clinical interest due to anticancer, multidrug therapies including both imatinib mesylate and cyclophosphamide.

Repurposing of genistein as anti-sickling agent: elucidation by multi spectroscopic, thermophoresis, and molecular modeling techniques

Sickle cell disease (SCD) is a major medical problem in which mono-therapeutic interventions have so far shown only limited effectiveness. We studied the repurpose of genistein, which could prevent sickle hemoglobin from polymerizing under hypoxic conditions in this disease. Genistein an important nutraceutical molecule found in soybean. The present study examines the repurposing genistein as an anti- sickling agent. Genistein shows inhibition of Hb S polymerization as well as a sickle reversal. Also, we have explored the interaction of the genistein with sickle hemoglobin (Hb S), using fluorescence, far-UV-CD spectroscopy, MicroScale Thermophoresis (MST), FTIR, combined with molecular modeling computations. The quenching constant decreases with increasing temperature, a characteristic that coincides with the static type of quenching mechanism. Temperature-dependent fluorescence measurements and molecular modeling studies reveal that apart from the hydrogen bonding, electrostatic interactions also play a crucial role in genistein and Hb S complex formation. In silico, distribution prediction of adsorption, digestion, metabolism, excretion, and toxicity (ADME/Tox) based on physical and chemical properties show that genistein is nontoxic and has ideal drug properties. The helicity and thermophoretic mobility of Hb S was a change in the presence of genistein, which leads to the destabilizing the Hb S polymer was examined using CD and MST, respectively. Our results open up the possibility for a promising therapeutic approach for the SCD by repurposed genistein as an anti-sickling agent.Communicated by Ramaswamy H. Sarma.

Comparative binding of Swertiamarin with human serum albumin and α-1 glycoprotein and its cytotoxicity against neuroblastoma cells

Communicated by Ramaswamy H. Sarma.

Potential of isoquercitrin as antisickling agent: a multi-spectroscopic, thermophoresis and molecular modeling approach

Sickle cell disease is an inherited disease caused by point mutation in hemoglobin (β-globin gene). Under oxygen saturation, sickle hemoglobin form polymers, leading to rigid erythrocytes. The transition of the blood vessels is altered and initiated by the adhesion of erythrocytes, neutrophils and endothelial cells. Sickle Hemoglobin (HbS) polymerization is a major cause in red blood cells (RBC), promoting sickling and destruction of RBCs. Isoquercitrin, a medicinal bioactive compound found in various medicinal plants, has multiple health benefits. The present study examines the potential of isoquercitrin as an anti-sickle agent, showing a significant decrease in the rate of polymerization as well as sickling of RBCs. Isoquercitrin-induced graded alteration in absorbance and fluorescence of HbS, confirmed their interaction. A negative value of ΔG° strongly suggests that it is a spontaneous exothermic reaction induced by entropy. Negative ΔH° and positive ΔS° predicted that hydrogen and hydrophobic binding forces interfered with a hydrophobic microenvironment of β6Val leading to polymerization inhibition of HbS. HbS-Isoquercitrin complex exhibits helical structural changes leading to destabilization of the HbS polymer as confirmed by CD spectroscopy. MST and DSC results indicate greater changes in thermophoretic mobility and thermal stability of sickle hemoglobin in the presence of isoquercitrin, respectively. These findings were also supported by molecular simulation studies using DOCK6 and GROMACS. Hence, we can conclude that isoquercitrin interacts with HbS through hydrogen bonding, which leads to polymerization inhibition. Consequently, isoquercitrin could potentially be used as a medication for the treatment of sickle cell disease.Communicated by Ramaswamy H. Sarma.

Utilization of circular dichroism and electrospray ionization mass spectrometry to understand the formation and conversion of G-quadruplex DNA at the human c-myb proto-oncogene

G-quadruplex DNAs are involved in a number of key biological processes, including gene expression, transcription, and apoptosis. The c-myb oncogene contains a number of GGA repeats in its promoter which forms G-quadruplex, thus it could be used as a target in cancer therapeutics. Several in-vitro studies have used Circular Dichroism (CD) spectroscopy or electrospray ionization mass spectrometry (ESI-MS) to demonstrate formation and stability of G-quadruplex DNA structure in the promoter region of human c-myb oncogene. The factors affecting the c-myb G-quadruplex structures were investigated, such as cations (i.e. K⁺, NH₄⁺ and Na⁺) and co-solutes (methanol and polyethylene glycol). The results indicated that the presence of cations and co-solutes could change the G-quadruplex structural population and promote its thermodynamic stabilization as indicated by CD melting curves. It indicated that the co-solutes preferentially stabilize the c-myb G-quadruplex structure containing both homo- and hetero-stacking. In addition, protopine was demonstrated as a binder of c-myb G-quadruplex as screened from a library of natural alkaloids using ESI-MS method. CD spectra showed that it could selectively stabilize the c-myb G-quadruplex structure compared to other six G-quadruplexes from tumor-related G-rich sequences and the duplex DNAs (both long and short-chain ones). The binding of protopine could induce the change in the G-quadruplex structural populations. Therefore, protopine with its high binding specificity could be considered as a precursor for the design of drugs to target and regulate c-myb oncogene transcription.

Peptide-surfactant interactions: A combined spectroscopic and molecular dynamics simulation approach

In the present contribution, we report a combined spectroscopic and computational approach aiming to unravel at atomic resolution the effect of the anionic SDS detergent on the structure of two model peptides, the α-helix TrpCage and the β-stranded TrpZip. A detailed characterization of the specific amino acids involved is performed. Monomeric (single molecules) and micellar SDS species differently interact with the α-helix and β-stranded peptides, emphasizing the different mechanisms occurring below and above the critical aggregation concentration (CAC). Below the CAC, the α-helix peptide is fully unfolded, losing its hydrophobic core and its Asp-Arg salt bridge, while the β-stranded peptide keeps its native structure with its four Trp well oriented. Above the CAC, the SDS micelles have the same effect on both peptides, that is, destabilizing the tertiary structure while keeping their secondary structure. Our studies will be helpful to deepen our understanding of the action of the denaturant SDS on peptides and proteins.

Molecular interaction of 2,4-diacetylphloroglucinol (DAPG) with human serum albumin (HSA): The spectroscopic, calorimetric and computational investigation

Drug molecule interaction with human serum albumin (HSA) affects the distribution and elimination of the drug. The compound, 2,4-diacetylphloroglucinol (DAPG) has been known for its antimicrobial, antiviral, antihelminthic and anticancer properties. However, its interaction with HSA is not yet reported. In this study, the interaction between HSA and DAPG was investigated through steady-state fluorescence, time-resolved fluorescence (TRF), circular dichroism (CD), Fourier transform infrared (FT-IR) spectroscopy, isothermal titration calorimetry (ITC), molecular docking and molecular dynamics simulation (MDS). Fluorescence spectroscopy results showed the strong quenching of intrinsic fluorescence of HSA due to interaction with DAPG, through dynamic quenching mechanism. The compound bound to HSA with reversible and moderate affinity which explained its easy diffusion from circulatory system to target tissue. The thermodynamic parameters from fluorescence spectroscopic data clearly revealed the contribution of hydrophobic forces but, the role of hydrogen bonds was not negligible according to the ITC studies. The interaction was exothermic and spontaneous in nature. Binding with DAPG reduced the helical content of protein suggesting the unfolding of HSA. Site marker fluorescence experiments revealed the change in binding constant of DAPG in the presence of site I (warfarin) but not site II marker (ibuprofen) which confirmed that the DAPG bound to site I. ITC experiments also supported this as site I marker could not bind to HSA-DAPG complex while site II marker was accommodated in the complex. In silico studies further showed the lowest binding affinity and more stability of DAPG in site I than in site II. Thus the data presented in this study confirms the binding of DAPG to the site I of HSA which may help in further understanding of pharmacokinetic properties of DAPG.

PEG and mPEG-anthracene conjugate with trypsin and trypsin inhibitor: hydrophobic and hydrophilic contacts

The conjugation of trypsin (try) and trypsin inhibitor (tryi) with poly(ethylene glycol) (PEG) and methoxypoly(ethylene glycol) anthracene (mPEG-anthracene) was investigated in aqueous solution, using multiple spectroscopic methods, thermodynamic analysis, and molecular modeling. Thermodynamic parameters ΔS, ΔH, and ΔG showed protein-PEG bindings occur via H-bonding and van der Waals contacts with trypsin inhibitor forming more stable conjugate than trypsin. As polymer size increased more stable PEG-protein conjugate formed, while hydrophobic mPEG-anthracene forms less stable protein complexes. Modeling showed the presence of several H-bonding contacts between polymer and amino acids that stabilize protein-polymer conjugation. Polymer complexation induces more perturbations of trypsin inhibitor structure than trypsin with reduction of protein alpha-helix and major increase in random structures, indicating protein structural destabilization.

Systematic studies of the interactions between a model polyphenol compound and microbial β-glucosidases

Lignin is a major obstacle for cost-effective conversion of cellulose into fermentable sugars. Non-productive adsorption onto insoluble lignin fragments and interactions with soluble phenols are important inhibition mechanisms of cellulases, including β-glucosidases. Here, we examined the inhibitory effect of tannic acid (TAN), a model polyphenolic compound, on β-glucosidases from the bacterium Thermotoga petrophila (TpBGL1 and TpBGL3) and archaeon Pyrococcus furiosus (PfBGL1). The results revealed that the inhibition effects on β-glucosidases were TAN concentration-dependent. TpBGL1 and TpBGL3 were more tolerant to the presence of TAN when compared with PfBGL1, while TpBGL1 was less inhibited when compared with TpBGL3. In an attempt to better understand the inhibitory effect, the interaction between TAN and β-glucosidases were analyzed by isothermal titration calorimetry (ITC). Furthermore, the exposed hydrophobic surface areas in β-glucosidases were analyzed using a fluorescent probe and compared with the results of inhibition and ITC. The binding constants determined by ITC for the interactions between TAN and β-glucosidases presented the same order of magnitude. However, the number of binding sites and exposed hydrophobic surface areas varied for the β-glucosidases studied. The binding between TAN and β-glucosidases were driven by enthalpic effects and with an unfavorable negative change in entropy upon binding. Furthermore, the data suggest that there is a high correlation between exposed hydrophobic surface areas and the number of binding sites on the inhibition of microbial β-glucosidases by TAN. These studies can be useful for biotechnological applications.

β-Lactoglobulin: An efficient nanocarrier for advanced delivery systems

Thanks to the progress of nanotechnology there are several agent-delivery systems that can be selected to achieve rapid and specific delivery of a wide variety of biologically active agents. Consequently, the manipulation and engineering of biopolymers has become one of the most exciting subjects for those who study delivery systems on the nanoscale. In this regard, both nanoparticle formation and a carrier role have been observed in the case of the globular milk whey protein, β-lactoglobulin (β-LG), setting it apart from many other proteins. To date, many efforts adopting different approaches have created β-LG nanoparticles useful in forming delivery systems for various agents with specific targets. In this review, the potential of β-LG to play the role of an efficient and diverse carrier protein, as well as its ability to form a well-targeted nano-scale delivery system is discussed.

Interaction between 8-methoxypsoralen and trypsin: Monitoring by spectroscopic, chemometrics and molecular docking approaches

8-Methoxypsoralen (8-MOP) is a naturally occurring furanocoumarin with various biological activities. However, there is little information on the binding mechanism of 8-MOP with trypsin. Here, the interaction between 8-MOP and trypsin in vitro was determined by multi-spectroscopic methods combined with the multivariate curve resolution-alternating least squares (MCR-ALS) chemometrics approach. An expanded UV-vis spectral data matrix was analysed by MCR-ALS, the concentration profiles and pure spectra for the three reaction species (trypsin, 8-MOP and 8-MOP-trypsin) were obtained to monitor the interaction between 8-MOP and trypsin. The fluorescence data suggested that a static type of quenching mechanism occurred in the binding of 8-MOP to trypsin. Hydrophobic interaction dominated the formation of the 8-MOP-trypsin complex on account of the positive enthalpy and entropy changes, and trypsin had one high affinity binding site for 8-MOP with a binding constant of 3.81×10⁴Lmol^-1 at 298K. Analysis of three dimensional fluorescence, UV-vis absorption and circular dichroism spectra indicated that the addition of 8-MOP induced the rearrangement of the polypeptides carbonyl hydrogen-bonding network and the conformational changes in trypsin. The molecular docking predicted that 8-MOP interacted with the catalytic residues His57, Asp102 and Ser195 in trypsin. The binding patterns and trypsin conformational changes may result in the inhibition of trypsin activity. This study has provided insights into the binding mechanism of 8-MOP with trypsin.

Optimization of Extraction Conditions for Maximal Phenolic, Flavonoid and Antioxidant Activity from Melaleuca bracteata Leaves Using the Response Surface Methodology

Melaleuca bracteata is a yellow-leaved tree belonging to the Melaleuca genus. Species from this genus are known to be good sources of natural antioxidants, for example, the “tea tree oil” derived from M. alternifolia is used in food processing to extend the shelf life of products. In order to determine whether M. bracteata contains novel natural antioxidants, the components of M. bracteata ethanol extracts were analyzed by gas chromatography–mass spectrometry. Total phenolic and flavonoid contents were extracted and the antioxidant activities of the extracts evaluated. Single-factor experiments, central composite rotatable design (CCRD) and response surface methodology (RSM) were used to optimize the extraction conditions for total phenolic content (TPC) and total flavonoid content (TFC). Ferric reducing power (FRP) and 1,1-Diphenyl-2-picrylhydrazyl radical (DPPH·) scavenging capacity were used as the evaluation indices of antioxidant activity. The results showed that the main components of M. bracteata ethanol extracts are methyl eugenol (86.86%) and trans-cinnamic acid methyl ester (6.41%). The single-factor experiments revealed that the ethanol concentration is the key factor determining the TPC, TFC, FRP and DPPH·scavenging capacity. RSM results indicated that the optimal condition of all four evaluation indices was achieved by extracting for 3.65 days at 53.26°C in 34.81% ethanol. Under these conditions, the TPC, TFC, FRP and DPPH·scavenging capacity reached values of 88.6 ± 1.3 mg GAE/g DW, 19.4 ± 0.2 mg RE/g DW, 2.37 ± 0.01 mM Fe²⁺/g DW and 86.0 ± 0.3%, respectively, which were higher than those of the positive control, methyl eugenol (FRP 0.97 ± 0.02 mM, DPPH·scavenging capacity 58.6 ± 0.7%) at comparable concentrations. Therefore, the extracts of M. bracteata leaves have higher antioxidant activity, which did not only attributed to the methyl eugenol. Further research could lead to the development of a potent new natural antioxidant.

Characterization of the binding of neomycin/paromomycin sulfate with DNA using acridine orange as fluorescence probe and molecular docking technique

The binding of neomycin sulfate (NS)/paromomycin sulfate (PS) with DNA was investigated by fluorescence quenching using acridine orange (AO) as a fluorescence probe. Fluorescence lifetime, FT-IR, circular dichroism (CD), relative viscosity, ionic strength, DNA melting temperature, and molecular docking were performed to explore the binding mechanism. The binding constant of NS/PS and DNA was 6.70 × 10³/1.44 × 10³ L mol^-1 at 291 K. The values of ΔH^θ, ΔS^θ, and ΔG^θ suggested that van der Waals force or hydrogen bond might be the main binding force between NS/PS and DNA. The results of Stern-Volmer plots and fluorescence lifetime measurements all revealed that NS/PS quenching the fluorescence of DNA-AO was static in nature. FT-IR indicated that the interaction between DNA and NS/PS did occur. The relative viscosity and melting temperature of DNA were almost unchanged when NS/PS was introduced to the solution. The fluorescence intensity of NS/PS-DNA-AO was decreased with the increase in the ionic strength. For CD spectra of DNA, the intensity of positive band at nearly 275 nm was decreased and that of negative band at nearly 245 nm was increased with the increase in the concentration of NS/PS. The binding constant of NS/PS with double-stranded DNA (dsDNA) was larger than that of NS/PS with single-stranded DNA (ssDNA). From these studies, the binding mode of NS/PS with DNA was evaluated to be groove binding. The results of molecular docking further indicated that NS/PS could enter into the minor groove in the A-T rich region of DNA.

Conjugation of biogenic and synthetic polyamines with serum proteins: A comprehensive review

We have reviewed the conjugation of biogenic polyamines spermine (spm), spermidine (spmd) and synthetic polyamines 3,7,11,15-tetrazaheptadecane.4HCl (BE-333) and 3,7,11,15,19-pentazahenicosane.5HCl (BE-3333) with human serum albumin (HSA), bovine serum albumin (BSA) and milk beta-lactoglobulin (b-LG) in aqueous solution at physiological pH. The results of multiple spectroscopic methods and molecular modeling were analysed here and correlations between polyamine binding mode and protein structural changes were estabilished. Polyamine-protein bindings are mainly via hydrophilic and H-bonding contacts. BSA forms more stable conjugates than HSA and b-LG. Biogenic polyamines form more stable complexes than synthetic polyamines except in the case of b-LG, where the protein shows more hydrophobic character than HSA and BSA. The loading efficacies were 40-52%. Modeling showed the presence of several H-bonding systems, which stabilized polyamine-protein conjugates. Polyamine conjugation induced major alterations of serum protein conformations. The potential application of serum proteins in delivery of polyamines is evaluated here.

Controlling the Ratio between Native-Like, Non-Native-Like, and Aggregated β-Lactoglobulin after Heat Treatment

The amount of heat-denatured whey protein is typically determined by pH 4.6 precipitation. Using this method, a significant amount of nondenatured protein was reported even after long heating times. Apparently, a fraction of the unfolded protein refolds into the "native" state rather than form aggregates. This fact is known and has been explained using kinetic models. How the conditions affect the refolding and aggregation is, however, not fully understood. Therefore, this study investigates the unfolding, refolding, and aggregation process of β-lactoglobulin using circular dichroism and size-exclusion chromatography to characterize different folding variants and to quantify their content. The proteins remaining in solution at pH 4.6 were confirmed to be native-like. The nonaggregated fraction contains proteins with a native-like and two types of non-native-like conformations. The nonaggregated fraction increased with decreasing temperature (60-90 °C) and concentration (1-50 g/L) and increasing electrostatic repulsion (pH 7-8; 0-50 mM). The native-like fraction in the nonaggregated fraction was independent of pH, ionic strength, and concentration but increased with decreasing temperature.

Review on the delivery of steroids by carrier proteins

Due to the poor solubility of steroids in aqueous solution, delivery of these biomaterials is of major biomedical importance. We have reviewed the conjugation of testosterone and it aliphatic dimer and aromatic dimer with several carrier proteins, human serum albumin (HSA), bovine serum albumin (BSA) and milk beta-lactoglobulin (b-LG) in aqueous solution at physiological pH. The results of multiple spectroscopic methods, transmission electron microscopy (TEM) and molecular modeling were compared here. Steroid-protein bindings are via hydrophilic and H-bonding contacts. HSA forms more stable conjugate than BSA and b-LG. The stability of steroid-protein conjugates is testosterone>dimer-aromatic>dimer-aliphatic. Encapsulation of steroids by protein is shown by TEM images. Modeling showed the presence of H-bonding, which stabilized testosterone-protein complexes with the free binding energy of -12.95 for HSA and -11.55 for BSA and -8.92kcal/mol for b-LG conjugates. Steroid conjugation induced major perturbations of serum protein conformations. Serum proteins can transport steroids to the target molecules.

The new insight into oral drug delivery system based on metal drugs in colon cancer therapy through β-lactoglobulin/oxali-palladium nanocapsules

Many efforts have been made to improve the targeting and potential applications of oral drug delivery systems. In this paper, we have demonstrated and investigated how biopolymer nanocapsules can be used as a novel oral drug delivery system for metal-based drug delivery in colon cancer therapy. In this work, β-lactoglobulin nanocapsules containing oxali-palladium were chosen to be synthesized and investigated for the use in colon cancer therapy. These nanocapsules were fabricated in three different pHs (3, 4.5 and 7) and investigated both in the presence and absence of low methoxyl pectin. The results obtained from these experiments indicated that the soluble and stable β-lactoglobulin nanocapsules which contained oxali-palladium had the ability to be formed at a size smaller than 200 nm when in the presence of low methoxyl pectin and at pH 4.5. The in vitro release data indicated that the maximum release occurs at pH 7.0 and 7.5. There lease mechanism demonstrated an anomalous diffusion with a predominant contribution from erosion. Finally, it can be concluded that the β-LG nanocapsules containing oxali-palladium complexed with low methoxyl pectin can be a very promising candidate for the use in oral drug delivery for colon cancer treatment.

Fucoidan as an inhibitor of thermally induced collagen glycation examined by acetate electrophoresis

Non-enzymatic glycation (Maillard reaction) in vitro could be a simple method to obtain glycoconjugates for studying their biological properties. Hence, fucoidan was retained by acetate electrophoresis indicating a strong interaction with the protein. A loss of colour in fucoidan bands was found for samples incubated with collagen as compared with samples of free fucoidan. Also under in vitro conditions at 100°C - simulating a sudden burn incident - fucoidan binds with collagen as a result of the Maillard reaction. In contrast, the colour of the fucoidan bands intensified for samples incubated with collagen, with the addition of glucose. Electrophoretic analyses were carried out after heating the samples to a temperature simulating a burn incident. The bands were found to intensify for samples incubated with collagen during a 30-day-long incubation. Thus, spontaneous in vitro glycation - i.e. without the addition of glucose - was confirmed. This process is highly intensified both by the temperature and time of incubation. For a sample incubated in vitro in a fucoidan solution containing glucose, glycation was confirmed in a preliminary FTIR and acetate electrophoresis examinations, occurring in collagen obtained from chicken skins. In particular, a new band emerging around 1746 cm(-1) was observed for above samples, as was its increasing intensity, as compared with samples without the addition of glucose. In the collagen glycation assay, while glucose reacts with collagen and forms cross-linked aggregates, fucoidan decreases the process of aggregation and recovery of native collagen.

Structure and dynamic properties of membrane proteins using NMR

Integral membrane proteins are one of the most challenging groups of macromolecules despite their apparent conformational simplicity. They manage and drive transport, circulate information, and participate in cellular movements via interactions with other proteins and through intricate conformational changes. Their structural and functional decoding is challenging and has imposed demanding experimental development. Solution nuclear magnetic resonance (NMR) spectroscopy is one of the techniques providing the capacity to make a significant difference in the deciphering of the membrane protein structure-function paradigm. The method has evolved dramatically during the last decade resulting in a plethora of new experiments leading to a significant increase in the scientific repertoire for studying membrane proteins. Besides solving the three-dimensional structures using state-of-the-art approaches, a large variety of developments of well-established techniques are available providing insight into membrane protein flexibility, dynamics, and interactions. Inspired by the speed of development in the application of new strategies, by invention of methods to measure solvent accessibility and describe low-populated states, this review seeks to introduce the vast possibilities solution NMR can offer to the study of membrane protein structure-function analyses with special focus on applicability.