Interaction of mitoxantrone with human serum albumin: Spectroscopic and molecular modeling studies

Structural and theoretical basis for drug development targeting TMEM16A: Inhibition mechanism of tracheloside analogs

Ion channels play a crucial role in the electrophysiological activities of organisms. The calcium-activated chloride channel TMEM16A is involved in various physiological processes. Therefore, inhibitors of TMEM16A are used to treat diseases caused by TMEM16A dysfunction. However, the unclear inhibition mechanism hinders the progress of drug development. Based on our previous study, we found that the molecular structures of TMEM16A inhibitors tracheloside, matairesinoside and arctigenin are similar. In this study, we conducted a structure-based virtual screening of tracheloside analogs from the PubChem database. The six tracheloside analogs with the highest affinity to TMEM16A were selected, and their inhibitory effects were detected by fluorescence and electrophysiological experiments. Subsequently, the interaction between the tracheloside analogs and TMEM16A was investigated through molecular docking and site-directed mutagenesis. Based on the above results, the mechanism of inhibition of TMEM16A gated conformation by tracheloside analogs was proposed. These findings provide a structural and theoretical basis for drug development targeting TMEM16A.

Insight into the effects of large yellow croaker roe (Larimichthys Crocea) phospholipids on the conformational and functional properties of pork myofibrillar protein

The large yellow croaker roe phospholipids (LYPLs), rich in polyunsaturated fatty acids, is a potential phospholipid additive for meat products. In this work, the effects of LYPLs on the structural and functional properties of myofibrillar protein (MP) were determined, and compared with egg yolk phospholipids (EYPLs) and soybean phospholipids (SBPLs). The results revealed that LYPLs, similar to SBPLs and EYPLs, induced a transformation in the secondary structure of MP from α-helix to β-sheets and random coils, while also inhibited the formation of carbonyl and disulfide bonds within MP. All three phospholipids induced MP tertiary structure unfolding, with the greatest degree of unfolding observed in MP containing LYPLs. The MP with LYPLs had the highest surface hydrophobicity, emulsification properties and gel strength. In addition, MP with LYPLs added also demonstrated superior rheological properties and water-holding capacity compared with SBPLs and EYPLs. In conclusion, adding LYPLs endowed MP with improved functional properties.

Inhibition mechanism of different structural polyphenols against α-amylase studied by solid-state NMR and molecular docking

Polyphenol has the considerable effects for inhibition of digestive enzymes, however, inhibition mechanism of molecular size-dependent polyphenols on enzyme activity is still lacking. Herein, inhibition effect and binding interactions of three different structural polyphenols (catechol, quercetin and hesperidin) on α-amylase were studied. Inhibition assays proved that polyphenols significantly inhibited α-amylase and their effects were increased with their molecular sizes. Hesperidin showed the highest inhibition ability of α-amylase, which was determined as IC50 = 0.43 mg/mL. Fluorescence and FT-IR spectroscopy proved that inter-molecular interactions between polyphenols and α-amylase occurred through non-covalent bonds. Besides, the secondary structure of α-amylase was obviously changed after binding with polyphenols. Inter-molecular interactions were investigated using solid-state NMR and molecular docking. Findings proved that hydrogen bonds and π-π stacking interactions were the mainly inter-molecular interactions. We hope this contribution could provide a theoretical basis for developing some digestive enzyme inhibitors from natural polyphenols.

Experimental and Theoretical Approaches to Monitor the Behavior of Bovine Liver Catalase in Interaction with a Binuclear Bismuth Complex

Here, the antioxidant potency of a binuclear Bi(III) complex {[Bi2(μ-ox)(dipic)2(H2O)2 (taa)2].H2O, where ox2- = oxalato, dipic2- = pyridine 2,6-dicarboxylato, and taa = thiourea} was evaluated using the •DPPH assay. It was demonstrated that the Bi complex exhibited a high ability to inhibit DPPH free radicals. The binding mechanism of the complex with bovine liver catalase (BLC) was also investigated, revealing structural and activity changes in the enzyme in the presence of the complex. The catalase activity in the decomposition of hydrogen peroxide increased in the presence of the Bi complex, reaching 39.8% higher than its initial activity at a concentration of 7.77 × 10-6 M. The complex exhibited a relatively high affinity for BLC, with K b values of 3.98, 0.13, and 0.09 × 105 M-1 at 303, 310, and 317 K, respectively. The mechanisms involved in the interaction were hydrogen bonding and van der Waals interactions, as validated through molecular docking simulations. Synchronous fluorescence showed that tryptophan was more affected by enzyme-complex interactions than tyrosine. In addition, a cell viability test using the MTT method revealed that at its highest concentration, the Bi complex caused a decrease in the number of cells below 50% compared to the control, while cisplatin showed negative effects at all concentrations. These findings suggest that the Bi complex has the potential to be developed as a promising candidate for BLC-related therapeutic target therapy.

Unveiling the Detrimental Effect of Glipizide on Structure and Function of Catalase: Spectroscopic, Thermodynamics and Simulation Studies

Free radicals, products of oxidative processes, induce cellular damage linked to diseases like Parkinson's and diabetes due to increased reactive oxygen species (ROS) levels. Catalase, crucial for scavenging ROS, emerges as a therapeutic agent against ailments including atherosclerosis and tumor progression. Its primary function involves breaking down hydrogen peroxide into water and oxygen. Research on catalase-drug interactions reveals structural changes under specific conditions, affecting its activity and cellular antioxidant balance, highlighting its pivotal role in defending against oxidative stress-related diseases. Hence, targeting catalase is considered an effective strategy for controlling ROS-induced cellular damage. This study investigates the interaction between bovine liver catalase and glipizide using spectroscopic and computational methods. It also explores glipizide's effect on catalase activity. More than 20% inhibition of catalase enzymatic activity was recorded in the presence of 50 µM glipizide. To investigate the inhibition of catalase activity by glipizide, we performed a series of binding studies. Glipizide was found to form a complex with catalase with moderate affinity and binding constant in the range of 3.822 to 5.063 × 104 M-1. The binding was spontaneous and entropically favourable. The α-helical content of catalase increased from 24.04 to 29.53% upon glipizide complexation. Glipizide binding does not alter the local environment surrounding the tyrosine residues while a notable decrease in polarity around the tryptophan residues of catalase was recorded. Glipizide interacted with numerous active site residues of catalase including His361, Tyr357, Ala332, Asn147, Arg71, and Thr360. Molecular simulations revealed that the catalase-glipizide complex remained relatively stable in an aqueous environment. The binding of glipizide had a negligible effect on the secondary structure of catalase, and hydrogen bonds persisted consistently throughout the trajectory. These results could aid in the development of glipizide as a potent catalase inhibitor, potentially reducing the impact of reactive oxygen species (ROS) in the human body.

Exploring the mechanism of interaction of glipizide with DNA: Combined in vitro and bioinformatics approach

DNA, vital for biological processes, encodes hereditary data for protein synthesis, shaping cell structure and function. Since revealing its structure, DNA has become a target for various therapeutically vital molecules, spanning antidiabetic to anticancer drugs. These agents engage with DNA-associated proteins, DNA-RNA hybrids, or bind directly to the DNA helix, triggering diverse downstream effects. These interactions disrupt vital enzymes and proteins essential for maintaining cell structure and function. Analysing drug-DNA interactions has significantly advanced our understanding of drug mechanisms. Glipizide, an antidiabetic drug, is known to cause DNA damage in adipocytes. However, its extract mechanism of DNA interaction is unknown. This study delves into the interaction between glipizide and DNA utilizing various biophysical tools and computational technique to gain insights into the interaction mechanism. Analysis of UV-visible and fluorescence data reveals the formation of complex between DNA and glipizide. The binding affinity of glipizide to DNA was of moderate strength. Examination of thermodynamic parameters at different temperatures suggests that the binding was entropically spontaneous and energetically favourable. Various experiments such as thermal melting assays, viscosity measurement, and dye displacement assays confirmed the minor grove nature of binding of glipizide with DNA. Molecular dynamics studies confirmed the glipizide forms stable complex with DNA when simulated by mimicking the physiological conditions. The binding was mainly favoured by hydrogen bonds and glipizide slightly reduced nucleotide fluctuations of DNA. The study deciphers the mechanism of interaction of glipizide with DNA at molecular levels.

Biological Evaluation and Binding Mechanism of 5-HT7 Specific Arylpiperazinyl-Alkyl Benzothiazolone: Radiobiology and Photo-physical Studies

Diversely substituted methoxy derivatives of arylpiperazinyl-alkyl benzothiazolone has been evaluated as specific probe for 5HT7. To determine the best methoxy derivative for 5HT7 receptor affinity, we synthesised a number of 2-benzothiazolone arylalkyl piperazine derivatives. In-vitro/vivo studies with C-2 substituted [11C]ABT showed 5HT7 specific binding. The radiochemical purity of [11C]ABT was found to be more than 99% with radiochemical stability persistence for more than 1.5 hr at 25 °C. The interaction of BSA and ABT has been analysed by photophysical studies for better understanding of properties such as adsortion, distribution, metabolism and elemination (ADME). The interaction between ABT and BSA was analyzed by using the UV-vis and fluorescence spectra. UV-vis spectra analyzed the changes in primary structure of BSA on its interaction with ABT. ABT showed quenched fluorescence emission intensity of tryptophan residues in BSA via static quenching mechanism. This study might help to understand how ABT binds to serum protein or subsequently to know the ADME of this drug candidate.

Comprehensive insight into the molecular interaction of rutin with human transferrin: Implication of natural compounds in neurodegenerative diseases

Neurodegeneration, a process of irreversible neuronal damage, is characterized by a damaged neuronal structure and function. The interplay between various proteins maintains homeostasis of essential metals in the brain, shielding neurons from degeneration; human transferrin (Htf) is essential in maintaining iron homeostasis. Any disruption in iron homeostasis results in the development of neurodegenerative diseases (NDs) and their pathology, mainly Alzheimer's disease (AD). Rutin is a known compound for its neuroprotective effects. In this work, we deciphered the binding of rutin with Htf in a bid to understand the interaction mechanism. The results of fluorescence and UV-vis spectroscopy demonstrated strong interaction between rutin and Htf. The enthalpy change (∆H°) and entropy change (∆S°) analysis demonstrated hydrophobic interactions as the prevalent forces. The binding mechanism of rutin was further assessed atomistically by molecular docking and extensive 200 ns molecular dynamic simulation (MD) studies; molecular docking showed binding of rutin within Htf's binding pocket. MD results suggested that binding of rutin to Htf does not cause significant structural switching or disruption of the protein's native packing. Overall, the study deciphers the binding of rutin with hTf, delineating the binding mechanism and providing a platform to use rutin in NDs therapeutics.

Aggregation and cytotoxicity of food additive dye (Azorubine)-albumin adducts: a multi-spectroscopic, microscopic and computational analysis

Protein and peptide misfolding is a central factor in the formation of pathological aggregates and fibrils linked to disorders like Alzheimer's and Parkinson's diseases. Therefore, it's essential to understand how food additives, particularly Azorubine, affect protein structures and their ability to induce aggregation. In this study, human serum albumin (HSA) was used as a model protein to investigate the binding and conformational changes caused by azorubine, a common food and drink colorant. The research revealed that azorubine destabilized the conformation of HSA at both physiological (pH 7.4) and acidic (pH 3.5) conditions. The loss of tryptophan fluorescence in HSA suggested significant structural alterations, particularly around aromatic residues. Far UV-CD analysis demonstrated disruptions in HSA's secondary structure, with a notable reduction in α-helical structures at pH 7.4. At pH 3.5, Azorubine induced even more extensive perturbations, resulting in a random coil conformation at higher azorubine concentrations. The study also investigated aggregation phenomena through turbidity measurements, RLS analysis, and TEM imaging. At pH 3.5, larger insoluble aggregates formed, while at pH 7.4, only conformational changes occurred without aggregate formation. Cytotoxicity assessments on neuroblastoma (SH-SY5Y) cells highlighted the concentration-dependent toxicity of albumin aggregates. Molecular dynamics simulations reaffirmed the stable interaction between azorubine and HSA. This research provides valuable insights into the mechanisms by which azorubine influences protein conformations. To further advance our understanding and contribute to the broader knowledge in this area, several future directions can be considered such as exploring other proteins, studying dose-response relationship, gaining mechanistic insights, biological relevance, toxicity assessment, identifying alternative food colorants, and mitigation strategies to prevent adverse effects of azorubine on serum proteins.Communicated by Ramaswamy H. Sarma.

Blood Compatibility of Drug-Inorganic Hybrid in Human Blood: Red Blood Cell Hitchhiking and Soft Protein Corona

A drug-delivery system consisting of an inorganic host-layered double hydroxide (LDH)-and an anticancer drug-methotrexate (MTX)-was prepared via the intercalation route (MTX-LDH), and its hematocompatibility was investigated. Hemolysis, a red blood cell counting assay, and optical microscopy revealed that the MTX-LDH had no harmful toxic effect on blood cells. Both scanning electron microscopy and atomic force microscopy exhibited that the MTX-LDH particles softly landed on the concave part inred blood cells without serious morphological changes of the cells. The time-dependent change in the surface charge and hydrodynamic radius of MTX-LDH in the plasma condition demonstrated that the proteins can be gently adsorbed on the MTX-LDH particles, possibly through protein corona, giving rise to good colloidal stability. The fluorescence quenching assay was carried out to monitor the interaction between MTX-LDH and plasma protein, and the result showed that the MTX-LDH had less dynamic interaction with protein compared with MTX alone, due to the capsule moiety of the LDH host. It was verified by a quartz crystal microbalance assay that the surface interaction between MTX-LDH and protein was reversible and reproducible, and the type of protein corona was a soft one, having flexibility toward the biological environment.

Comparative study of the interaction mechanism of astilbin, isoastilbin, and neoastilbin with CYP3A4

The interactions of human CYP3A4 with three selected isomer flavonoids, such as astilbin, isoastilbin and neoastilbin, were clarified using spectral analysis, molecular docking, and molecular dynamics simulation. During binding with the three flavonoids, the intrinsic fluorescence of CYP3A4 was statically quenched in static mode with nonradiative energy conversion. The fluorescence and ultraviolet/visible (UV/vis) data revealed that the three flavonoids had a moderate and stronger binding affinity with CYP3A4 due to the order of the Ka1 and Ka2 values ranging from 104 to 105  L·mol-1 . In addition, astilbin had the highest affinity with CYP3A4, then isoastilbin and neoastilbin, at the three experimental temperatures. Multispectral analysis confirmed that binding of the three flavonoids resulted in clear changes in the secondary structure of CYP3A4. It was found from fluorescence, UV/vis and molecular docking analyses that these three flavonoids strongly bound to CYP3A4 by means of hydrogen bonds and van der Waals forces. The key amino acids around the binding site were also elucidated. Furthermore, the stabilities of the three CYP3A4 complexes were evaluated using molecular dynamics simulation.

Studying the Mechanism of Interaction of Doxofylline with Human Lysozyme: A Biophysical and In Silico Approach

In this study, multiple spectroscopic and computational methods were utilized to investigate the binding mechanism of doxofylline with lysozyme. The in vitro methods were used to obtain the binding kinetics and thermodynamics. UV-vis spectroscopy indicated the formation of complex between doxofylline and lysozyme. The Gibb's free energy and binding constant from UV-vis data was obtained as -7.20 kcal M^-1 and 1.929 × 10⁵ M^-1, respectively. Doxofylline successfully quenched the fluorescence of lysozyme, confirming the formation of complex. The k_q and K_sv values for the quenching of lysozyme's fluorescence by doxofylline were 5.74 × 10¹¹ M^-1 s^-1 and 3.32 × 10³ M^-1, respectively. These values signified a moderate binding affinity between doxofylline and lysozyme. In synchronous spectroscopy, red shifts were observed for indicating the changes in microenvironment of lysozyme following the binding of doxofylline. The secondary structural analysis was determined using circular dichroism (CD) which revealed an increase in % α-helical as a result of doxofylline interaction. The binding affinity and flexibility of lysozyme upon complexation have been revealed via molecular docking and molecular dynamic (MD) simulations, respectively. According to the many parameters of the MD simulation, the lysozyme-doxofylline complex was stable under physiological conditions. All during the simulation time, hydrogen bonds were continuously present. The MM-PBSA binding energy for lysozyme and doxofylline binding was found to be -30.55 kcal mol^-1.

Affinity purification, identification, and biochemical characterization of Gamma-glutamyl transpeptidase, a membrane anchored enzyme of Gigantocotyle explanatum

Gamma-glutamyl transpeptidase is an enzyme that facilitates the transfer of glutamyl groups from glutamyl peptides to other peptides or water. Additionally, it also participates in important processes such as amino acid transport, cellular redox control, drug detoxification, apoptosis, and DNA fragmentation in a various organism. In the present study, GGT activity in Gigantocotyle explanatum was examined in order to characterize the enzyme in the helminth system. GGT is isolated using membrane solubilization and purified through affinity column chromatography (Con-A Sepharose column). Km and Vmax values, as well as the optimal pH, optimal temperature, and incubation period, are also determined using enzyme kinetics. The hetero-dimeric property of the enzyme is demonstrated by the purified GGT, which yielded two subunits of 65.5 and 55 kDa. The optimal pH and temperature are found to be 8.0 and 37 °C, respectively. While assessing the optimal incubation time of the enzyme, it was observed that the purified GGT not only retained its functional integrity up to 15 min but also reflected considerable thermostability at higher temperatures, by retaining 78% and 25% of its initial activities at 50 °C and 60 °C, respectively. One millimolar concentration of 6-Diazo-5-Oxo Nor-isoleucine (DON), a specific inhibitor of GGT, completely abolished GGT activity. These results suggest that GGT in these worms is a catalytically active enzyme with distinguishing characteristics that can be used for further study to comprehend its function in amphistome biology and in host-parasite relationships, especially since the potential therapeutic candidacy of the GGT enzyme has already been indicated in these groups of organisms.

The influence of several nutritional supplements on the rational use of cabozantinib

To promote the rational use of cabozantinib (CBZ), this paper studied the influence of several nutritional supplements on the interaction between CBZ and bovine serum albumin (BSA), an appropriate alternative model for human serum albumin (HSA) that is one of the important transporter proteins in plasma, by fluorescence spectroscopy and UV-vis spectroscopy. The results showed that CBZ could quench the fluorescence of BSA via a dynamic-static quenching process, and the six nutritional supplements did not change the quenching mode of BSA by CBZ. However, all of them could reduce the binding constant of the CBZ-BSA system at 293 K and increase the polarity around tryptophan residues. Among them, nicotinamide and vitamin B₁₂ (VB₁₂ ) had a greater effect on the binding constants of the CBZ-BSA system. In the meantime, the thermodynamic parameters of the CBZ-BSA system were examined, indicating that the interaction of CBZ with BSA was spontaneous and dominated by hydrophobic forces. Further research discovered that the combining of CBZ with BSA was primarily located within Site I of BSA, and the binding distance r was 2.48 nm. Consequently, while taking CBZ, patients should use VB₁₂ and nicotinamide carefully, which may interfere with the transport of drugs.

Characteristics and structure of a soy protein isolate-lutein nanocomplex produced via high-pressure homogenization

BACKGROUND

In recent years, nanocarriers for transporting active substances have attracted attention. This study was to explore the soy protein isolate (SPI) after high-pressure homogenization (HPH) (0, 30, 60, 90 and 120 MPa) as potential lutein carriers.

RESULTS

The load amount (LA) and encapsulation efficiency (EE) of the SPI-lutein nanocomplexes at a homogenization pressure of 60 MPa were the highest (2.32 mg mL^-1 and 92.85%, respectively), and the average particle size and ζ-potential of the SPI-lutein nanocomplexes were 192.1 nm and -30.06 mV, respectively. The DPPH (2,2-diphenyl-1-picrylhydrazyl) and hydroxyl-antioxidant activities of the complex increased from 12.4% and 23.3% to 52.7% and 61.07%, respectively, after the protein was treated with HPH. The surface hydrophobicity of the SPI and the SPI-lutein nanocomplexes increased with increasing homogenization pressure treatment. Fourier transform-infrared spectrophotometry analyses suggested that the homogenization treatments resulted in partial unfolding of the protein molecules, and the addition of lutein can also lead to the change of protein secondary structure. The fluorescence emission of SPI was quenched by lutein through the static quenching mechanism. Fluorescence experiments revealed that SPI and lutein had the strongest binding ability through hydrophobic interaction at a homogenization pressure of 60 MPa.

CONCLUSION

After HPH, the combination of SPI and lutein was beneficial, and the stability of lutein also improved after the combination. This study is conducive to expanding the application of soybean protein in the food industry. © 2022 Society of Chemical Industry.

The inhibitory kinetics and mechanism of quercetin-3-O-rhamnoside and chlorogenic acid derived from Smilax china L. EtOAc fraction on xanthine oxidase

Smilax china L. showed various biological activities mainly due to its phenolic components; however, the mechanism of isolated phenolic fraction against xanthine oxidase (XO) has not been investigated. Quercetin-3-O-rhamnoside (QORh) and chlorogenic acid (CGA) extracted from Smilax china L. ethyl acetate fraction was analyzed for its XO inhibitory kinetics and mechanism using multispectroscopic methods and molecular docking techniques. QORh and CGA reversibly inhibited XO activity in competitive and non-competitive modes, respectively. The bioactive compounds bound with XO were dominated mainly by hydrogen bonds and van der Waals forces to form QORh-XO, and CGA-XO complexes with one affinity binding site. The synchronous fluorescence, circular dichroism, three-dimensional (3D) fluorescence, and Fourier transform infrared spectra exhibited that XO binding with QORh or CGA leads to the secondary and tertiary structural variation of the protein. Additionally, molecular docking further revealed that QORh binds to the active site of XO and forms hydrogen coupling with amino acid residues. The results showed that QORh and CGA had inhibitory activity on XO, which might be further used to modify the bioactive compounds and improve their efficacy to treat gout.

Binding Studies of Caffeic and p-Coumaric Acid with α-Amylase: Multispectroscopic and Computational Approaches Deciphering the Effect on Advanced Glycation End Products (AGEs)

Alpha-amylase (α-amylase) is a key player in the management of diabetes and its related complications. This study was intended to have an insight into the binding of caffeic acid and coumaric acid with α-amylase and analyze the effect of these compounds on the formation of advanced glycation end-products (AGEs). Fluorescence quenching studies suggested that both the compounds showed an appreciable binding affinity towards α-amylase. The evaluation of thermodynamic parameters (ΔH and ΔS) suggested that the α-amylase-caffeic/coumaric acid complex formation is driven by van der Waals force and hydrogen bonding, and thus complexation process is seemingly specific. Moreover, glycation and oxidation studies were also performed to explore the multitarget to manage diabetes complications. Caffeic and coumaric acid both inhibited fructosamine content and AGE fluorescence, suggesting their role in the inhibition of early and advanced glycation end-products (AGEs). However, the glycation inhibitory potential of caffeic acid was more in comparison to p-coumaric acid. This high antiglycative potential can be attributed to its additional –OH group and high antioxidant activity. There was a significant recovery of 84.5% in free thiol groups in the presence of caffeic acid, while coumaric attenuated the slow recovery of 29.4% of thiol groups. In vitro studies were further entrenched by in silico studies. Molecular docking studies revealed that caffeic acid formed six hydrogen bonds (Trp 59, Gln 63, Arg 195, Arg 195, Asp 197 and Asp 197) while coumaric acid formed four H-bonds with Trp 59, Gln 63, Arg 195 and Asp 300. Our studies highlighted the role of hydrogen bonding, and the ligands such as caffeic or coumaric acid could be exploited to design antidiabetic drugs.

Insight into the Molecular Mechanism for the Discrepant Inhibition of Microcystins (MCLR, LA, LF, LW, LY) on Protein Phosphatase 2A

Microcystins (MCs) exhibit diversified inhibition effects on protein phosphatases (PPs) due to their structural differences. To fully evaluate the potential mechanism for the discrepant inhibition effects, the five most frequent MCs with varying residues at position Z4 were selected as the tested toxins. Their inhibition sequence on PP2A was detected as follows: MCLR > MCLW > MCLA > MCLF > MCLY. Combined with homology modeling and molecular docking technology, the major interaction parameters between the MCs and PP2A were obtained. The correlation analysis for the major interaction parameters and inhibition effects showed that the hydrophobicity of Z4 had an important influence on the interaction of the MCs to PP2A. The introduction of hydrophobic Z4 directly weakened hydrogen bonds Z4→Pro213 and Z4←Arg214, indirectly weakened hydrogen bonds Adda5←Asn117, Glu6←Arg89, and MeAsp3←Arg89, but indirectly enhanced ionic bonds Glu6←Arg89, Glu6-Mn12+, and Glu6-Mn22+. In this way, the combination of the MCs with PP2A was blocked, and thus, the interactions between PP2A and the Mn2+ ions (in the catalytic center) were further affected; metal bonds Asp85-Mn12+ and Asp85-Mn22+ were weakened, while metal bond His241-Mn12+ was enhanced. As a result, the interactions in the catalytic center were inhibited to varying degrees, resulting in the reduced toxicity of MCs.

Response of earthworm coelomocytes and catalase to pentanone and hexanone: a revelation of the toxicity of conventional solvents at the cellular and molecular level

Organic solvents like 2-pentanone and 2-hexanone which are widely used in industrial production make up a large proportion of the source of chemical pollution. What is worrisome is that the cellular and molecular toxicity of 2-pentanone and 2-hexanone has not been reported yet. Based on this, earthworms and catalase (CAT) were chosen as target receptors for the toxicity studies. The cytotoxicity of 2-pentanone and 2-hexanone was revealed by measuring the multiple intracellular indicators of oxidative stress. At the molecular level, changes in the structure and function of CAT were characterized in vitro by the spectroscopy and molecular docking. The results show that 2-pentanone and 2-hexanone that induced the accumulation of reactive oxygen species can eventually reduce coelomocytes viability, accompanying by the regular changes of antioxidant activity and lipid peroxidation level. In addition, the exposure of 2-pentanone and 2-hexanone can shrink the backbone structure of CAT, quench the fluorescence, and misfold the secondary structure. The decrease in enzyme activity should be attributed to the structural changes induced by surface binding. This study discussed the toxicological effects and mechanisms of conventional solvents at the cellular and molecular level, which creatively proposed a joint research method.

The breakdown of protein hydrogen bonding networks facilitates biotransformation of protein wastewaters during anaerobic digestion methanogenesis: Focus on protein structure and conformation

The low methanogenic efficiency of protein wastewater during anaerobic digestion can be attributed to the hydrolysis rate-limiting caused by the complex native structure of protein. In this study, the characterization of secondary structure alterations of protein molecules under acid-base stress was investigated and the effect of structure and conformation alterations on the methanogenic efficiency of protein wastewater biotransformation was analyzed. The optimal methane yields were obtained for protein wastewater pretreated with acid and base at pH = 3 and pH = 12, which was 29.4% and 35.7% higher than that of the control group (without pretreatment), reaching 142.6 ± 4.0 mL/g protein and 149.6 ± 16.1 mL/g protein, respectively. The time economy evaluation showed that 6 h pretreatment time was scientific and reasonable whether pH = 3 or pH = 12, since the methane gain effect reached 74.4% and 82.2% longing with the anaerobic digestion proceeded to 120 h, respectively. Endogenous fluorescence characteristics illustrated that the microenvironment of protein molecules has changed regardless of acid or alkali pretreatment. The circular dichroism (CD) analysis revealed that only the content of α-helix in the secondary structure of the protein at pH = 12 decreased by 46.3%, while the contents of β-sheet, β-turn and unordered structure were 29.5 ± 0.8%, 18.9 ± 0.6% and 32.2 ± 1.3%, respectively. The increase in the composition of the unordered structure demonstrated an irreversible damage to the hydrogen bonding network in the protein. FTIR spectroscopy further confirmed that the stretching vibrations of CO in amide I led to the destruction of the hydrogen bonding network and the unfolding of the protein structure. Thus, the above work provides new insights into the anaerobic digestion of protein wastewater for methanogenic processes from the perspective of protein structure and conformational changes.

Elucidating the Interactions of Fluoxetine with Human Transferrin Employing Spectroscopic, Calorimetric, and In Silico Approaches: Implications of a Potent Alzheimer's Drug

Neurodegenerative complexities, such as dementia, Alzheimer's disease (AD), and so forth, have been a crucial health concern for ages. Transferrin (Tf) is a chief target to explore in AD management. Fluoxetine (FXT) presents itself as a potent anti-AD drug-like compound and has been explored against several diseases based on the drug repurposing readings. The present study delineates the binding of FXT to Tf employing structure-based docking, molecular dynamics (MD) simulations, and principal component analysis (PCA). Docking results showed the binding of FXT with Tf with an appreciable binding affinity, making various close interactions. MD simulation of FXT with Tf for 100 ns suggested their stable binding without any significant structural alteration. Furthermore, fluorescence-based binding revealed a significant interaction between FXT and Tf. FXT binds to Tf with a binding constant of 5.5 × 105 M-1. Isothermal titration calorimetry (ITC) advocated the binding of FXT to Tf as spontaneous in nature, affirming earlier observations. This work indicated plausible interactions between FXT and Tf, which are worth considering for further studies in the clinical management of neurological disorders, including AD.

Inhibition of porphyra polysaccharide on xanthine oxidase activity and its inhibition mechanism

Xanthine oxidase (XO) is a purine catabolic enzyme related to hyperuricemia and gout. Porphyra polysaccharide (PP) is a kind of sulfated polysaccharide with potent biological activity. Herein, the interaction mechanism between PP and XO was studied by enzyme kinetics and multi-spectroscopy methods for the first time. Inhibition kinetics assay showed that PP reversibly inhibited XO activity in a mixed competitive manner with an IC₅₀ of 10.53 ± 0.69 mg/ml. Fluorescence titration studies and thermodynamic parameter calculations revealed that PP could spontaneously bind to XO through hydrophobic interactions, with a class of binding site. Circular dichroism analysis demonstrated that PP induced secondary structure rearrangement and conformational change of XO. Molecular docking further revealed that PP inserted into the hydrophobic cavity of XO, occupying the catalytic center, leading to the inhibition of XO activity. This study may provide new insights into the inhibitory mechanism of PP as a promising XO inhibitor.

Myricetin inhibits breast and lung cancer cells proliferation via inhibiting MARK4

Identifying novel molecules as potential kinase inhibitors are gaining significant attention globally. The present study suggests Myricetin as a potential inhibitor of microtubule-affinity regulating kinase (MARK4), adding another molecule to the existing list of anticancer therapeutics. MARK4 regulates initial cell division steps and is a potent druggable target for various cancers. Structure-based docking with 100 ns molecular dynamics simulation depicted activity of Myricetin in the active site pocket of MARK4 and the formation of a stable complex. The fluorescence-based assay showed excellent affinity of Myricetin to MARK4 guided by static and dynamic quenching. Moreover, the assessment of enthalpy change (∆H) and entropy change (∆S) delineated electrostatic interactions as a dominant force in the MARK4-myricetin interaction. Isothermal titration calorimetric measurements revealed spontaneous binding of Myricetin with MARK4. Further, the kinase assay depicted significant inhibition of MARK4 by Myricetin with IC₅₀  = 3.11 µM. Additionally, cell proliferation studies established that Myricetin significantly inhibited the cancer cells (MCF-7 and A549) proliferation, and inducing apoptosis. This study provides a solid rationale for developing Myricetin as a promising anticancer molecule in the MARK4 mediated malignancies.

Structural requirements of flavonoids for the selective inhibition of α-amylase versus α-glucosidase

In the present study, 14 structurally unique flavonoids were screened to systematically investigate structural requirements for selectively inhibiting human α-amylase versus α-glucosidase to obtain a slow but complete starch digestion for health benefit. The selective inhibition property of three flavonoids chosen against the two classes of starch digestive enzymes was confirmed through various analytical techniques - in vitro inhibition assay, fluorescence quenching, kinetic study, and molecular modeling. Considering the chemical structure of flavonoids, the double bond between C2 and C3 and OH groups at A5 and B3 are critical for the inhibition of α-amylase allowing flavonoids to lie parallel on the α-amylase catalytic active site, whereas the OH groups at B3 and C3 are important for α-glucosidase inhibition causing B-ring specific entry into the catalytic active site of α-glucosidase. Our findings provide insights into how to apply flavonoids to effectively control digestion rate for improving physiological responses.

Elucidation of molecular interactions of theaflavin monogallate with camel milk lactoferrin: detailed spectroscopic and dynamic simulation studies

Lactoferrin is a heme-binding multifunctional glycoprotein known for iron transportation in the blood and also contributes to innate immunity. In this study, the interaction of theaflavin monogallate, a polyphenolic component of black tea, with camel milk lactoferrin was studied using various biophysical and computational techniques. Fluorescence quenching at different temperatures suggests that theaflavin monogallate interacted with lactoferrin by forming a non-fluorescent complex, i.e., static quenching. Theaflavin monogallate shows a significant affinity towards lactoferrin with a binding constant of ∼10⁴–10⁵ M⁻¹ at different temperatures. ANS binding shows that the binding of polyphenol resulted in the burial of hydrophobic domains of lactoferrin. Moreover, thermodynamic parameters (ΔH, ΔS and ΔG) suggested that the interaction between protein and polyphenol was entropically favored and spontaneous. Circular dichroism confirmed there was no alteration in the secondary structure of lactoferrin. The energy transfer efficiency (FRET) from lactoferrin to theaflavin was found to be approximately 50%, with a distance between protein and polyphenol of 2.44 nm. Molecular docking shows that the binding energy of lactoferrin–theaflavin monogallate interaction was −9.7 kcal mol⁻¹. Theaflavin monogallate was bound at the central cavity of lactoferrin and formed hydrogen bonds with Gln89, Tyr192, Lys301, Ser303, Gln87, and Val250 of lactoferrin. Other residues, such as Tyr82, Tyr92, and Tyr192, were involved in hydrophobic interactions. The calculation of various molecular dynamics simulations parameters indicated the formation of a stable complex between protein and polyphenol. This study delineates the binding mechanism of polyphenol with milk protein and could be helpful in milk formulations and play a key role in the food industry.

Lactoferrin is a heme-binding multifunctional glycoprotein known for iron transportation in the blood and also contributes to innate immunity.

Mechanistic insight into the binding of graphene oxide with human serum albumin: Multispectroscopic and molecular docking approach

Increasing manufacturing and use of nanoparticles in industrial and biomedical applications creates the necessity to understand the impact of the interaction of nanoparticles with biomacromolecules. In the present study, graphene oxide nanosheets (GONS) were synthesized using modified Hummer's method and further characterized employing X-ray diffraction (XRD), UV, FTIR, and Raman spectroscopy. After characterization, the interaction of GONS with human serum albumin (HSA) was investigated to delineate the binding mechanism employing different kinds of spectroscopic techniques. Intrinsic fluorescence spectroscopy revealed that complex formation is taking place between HSA and GONS. Fluorescence-based binding studies suggested that GONS binds to HSA with a significant binding affinity, and the interaction is governed by dynamic quenching. The evaluation of enthalpy change (ΔH) and entropy change (ΔS) suggested that the HSA-GONS complex formation is driven by hydrogen bonding and van der Waals interaction and hence complexation process is seemingly specific. Structural transition in the microenvironment of HSA was monitored using synchronous fluorescence spectroscopy and three-dimensional fluorescence spectroscopy, which showed that GONS binding to HSA influences the microenvironment around tyrosine and tryptophan residues. Secondary structural alterations in HSA upon binding to GONS were measured using circular dichroism (CD) spectroscopy. Additionally, molecular docking provided an insight into the critical residues involved in HSA-GONS interaction and further validated our in vitro observations affirming interaction between GONS and HSA. The significance of this study is attributable to the fact that HSA and GONS can be used as nanocarriers in drug delivery systems.

Interaction study of astilbin, isoastilbin and neoastilbin toward CYP2D6 by multi-spectroscopy and molecular docking

Astilbin, isoastilbin and neoastilbin are the three flavonoid isomers prevalent in Rhizoma Smilax glabra. The interactions between human cytochrome P450 2D6 (CYP2D6) and the three isomers were investigated by multiple spectroscopic coupled with molecular docking. As a result, the fluorescence intensity of CYP2D6 was quenched statically by the three isomers. Meanwhile, astilbin had the strongest binding ability to CYP2D6, followed by isoastilbin and neoastilbin under the identical temperature. Synchronous fluorescence, three-dimensional fluorescence, ultraviolet-visible spectroscopy, circular dichroism and Fourier-transform infrared spectra confirmed that the conformation and micro-environment of CYP2D6 protein were changed after binding with the three isomers. As suggested from molecular docking, the three isomers had strong binding affinity to CYP2D6 via the bonding of hydrogen and van der Waals forces, and the results were in agreement with the fluorescence results. The findings here suggested that astilbin, isoastilbin and neoastilbin may cause the herb-drug interactions for their inhibition of CYP2D6 activity.

Insights into Multifunctional Nanoparticle-Based Drug Delivery Systems for Glioblastoma Treatment

Glioblastoma (GB) is an aggressive cancer with high microvascular proliferation, resulting in accelerated invasion and diffused infiltration into the surrounding brain tissues with very low survival rates. Treatment options are often multimodal, such as surgical resection with concurrent radiotherapy and chemotherapy. The development of resistance of tumor cells to radiation in the areas of hypoxia decreases the efficiency of such treatments. Additionally, the difficulty of ensuring drugs effectively cross the natural blood-brain barrier (BBB) substantially reduces treatment efficiency. These conditions concomitantly limit the efficacy of standard chemotherapeutic agents available for GB. Indeed, there is an urgent need of a multifunctional drug vehicle system that has potential to transport anticancer drugs efficiently to the target and can successfully cross the BBB. In this review, we summarize some nanoparticle (NP)-based therapeutics attached to GB cells with antigens and membrane receptors for site-directed drug targeting. Such multicore drug delivery systems are potentially biodegradable, site-directed, nontoxic to normal cells and offer long-lasting therapeutic effects against brain cancer. These models could have better therapeutic potential for GB as well as efficient drug delivery reaching the tumor milieu. The goal of this article is to provide key considerations and a better understanding of the development of nanotherapeutics with good targetability and better tolerability in the fight against GB.

Multispectroscopic and Molecular Docking Insight into Elucidating the Interaction of Irisin with Rivastigmine Tartrate: A Combinational Therapy Approach to Fight Alzheimer's Disease

This study was aimed to study the interaction between purified irisin and rivastigmine tartrate (RT), a cholinesterase inhibitor used in Alzheimer's therapy. Irisin mainly promotes brown fat-like features in white adipose tissues; however, it has some important role in the nervous system also, i.e., capable of opposing synapse and memory failure in Alzheimer's disease (AD). The recombinant protein was purified by Ni-NTA chromatography and characterized using spectroscopic and in silico techniques. Further, the mechanism of interaction between irisin and RT was investigated using various biophysical techniques. Fluorescence quenching studies suggested that there exists a moderate binding between irisin and RT with a binding constant (K) of 10⁴ M^-1 and the irisin-RT complex is guided by a combination of both static and dynamic modes of quenching. Thermodynamic parameters suggested the reaction to be driven by hydrogen bonding, making it specific. FTIR and CD spectroscopy suggested no secondary structural alterations in irisin in the presence of RT. Molecular docking investigation provided an insight into the important residues that play a key role in irisin-RT interactions. This study delineates an important finding in AD therapy and can provide a platform further to explore the potential of irisin in AD treatment.

Monosaccharides interact weakly with human serum albumin. Insights for the functional perturbations on the binding capacity of albumin

Monosaccharides, e.g. fructose, glucose, and arabinose are present in most foods consumed daily, whether, in natural or industrialized forms, and their concentration in the human bloodstream can impact the formation of advanced glycation end-products (AGEs, prevalent in people with diabetes) impacting the profile of Human Serum Albumin (HSA) in biodistribution of endogenous and exogenous compounds. Multiple spectroscopic techniques (UV-vis, circular dichroism, steady-state, and time-resolved fluorescence) combined with molecular docking showed that carbohydrates interact weakly and spontaneously via a ground-state association with HSA. The binding is enthalpically and entropically driven in the subdomain IIA (site I) and perturb weakly the secondary structure of the albumin. Hydrogen bonding and van der Waals forces are the main intermolecular interactions involved in the ligand binding, as well as hydrophobic effects related to the release of hydration shell upon ligand binding. Overall, the results indicated that an increase in glucose, fructose or arabinose level in the human bloodstream may cause functional perturbation on the binding capacity of albumin. Therefore, there is the necessity of carbohydrate level control in the bloodstream to not compromise the interaction and distribution of exogenous and endogenous compounds by HSA.

Shedding light on the bimolecular interactions of Cafaminol and human serum albumin: spectroscopic characterization and in-silico investigation

Cafaminol, also known as methylcoffanolamine, is a vasoconstrictor and anticatarrhal of the methylxanthine family, which is used as a nasal decongestant. This study aimed to investigate the interaction mechanisms of human serum albumin (HSA) with Cafaminol, through several spectroscopic (fluorescence quenching, UV-visible absorption, and circular dichroism (CD) spectroscopies) and molecular modeling techniques. Stern-Volmer plots were employed to specify the fluorescence quenching mechanism, while the simulation methods were utilized to deduce the approximate binding position of Cafaminol on HSA. On the other hand, thermodynamic parameters, enthalpy and entropy changes, were determined to be, respectively, -105.88 (kJ mol^-1) and -282.34 (J mol^-1 K^-1), using the Van't Hoff equation and analyzed later to specify the main acting forces between Cafaminol and HSA. Overall results revealed the binding of Cafaminol to the site I of HSA, as a result of an enthalpy-driven process, mainly through the van der Waals and hydrogen bonding interactions. Static quenching mechanism was found to be responsible for the fluorescence quenching of HSA in the Cafaminol presence, while the number of binding sites and apparent binding constant were measured accordingly. Docking results proposed that Cafaminol and HSA interact with a binding free energy (ΔG) of -6.5 kcal mol^-1Communicated by Ramaswamy H. Sarma.

Inhibition of non-enzymatic glycation by capsaicin: targeting AGE-induced diabetic complications

Capsaicin inhibits the non-enzymatic glycation of human serum albumin.

An albumin-binding Gd-HPDO3A contrast agent for improved intravascular retention

A new Gd-HPDO3A derivative with improved MR contrast enhancing efficiency, demonstrated in a murine tumor model and in mouse models for stable and vulnerable atherosclerotic plaques, due to increased intravascular retention.

Ex vivo binding studies of the anti-cancer drug noscapine with human hemoglobin: a spectroscopic and molecular docking study

Noscapine binds human hemoglobin spontaneously forming a stable complex that affects noscapine's ADMET profile, bioavailability and toxicity.

Glyburide inhibits non-enzymatic glycation of HSA: An approach for the management of AGEs associated diabetic complications

Advanced glycation endproducts (AGEs) are the final product of glycation, highly reactive in nature and contribute directly or indirectly to numerous complications related to diabetes. In this study, the antiglycation activity of glyburide was investigated using HSA as model protein, both against glucose and methylglyoxal mediated glycation. The possible mechanism of action was also deciphered using biophysical and computational tools. Approximately 70% inhibition of both early and advanced glycation end products were recorded in the presence of glyburide. Free lysine modification was reduced by glyburide treatment and improvement in biochemical markers such as free thiol groups and carbonyl content was observed. Interaction studies revealed that glyburide showed moderate to strong binding affinity towards HSA with binding constant in the order of 10⁶ M^-1. The interaction of glyburide with HSA was entropically favourable and spontaneous in nature. Molecular dynamics simulation deciphered that glyburide-HSA complex was quite stable where RMSD, RMSF, R_g, SASA, and secondary structure of HSA remained approximately same over the entire simulation period. The average binding energy of the MD simulation for glyburide-HSA complex was found to be -15.386 kJ mol^-1. The findings demonstrate the antiglycation potential of glyburide and its possible mechanism of action.

Evaluation of Binding of Rosmarinic Acid with Human Transferrin and Its Impact on the Protein Structure: Targeting Polyphenolic Acid-Induced Protection of Neurodegenerative Disorders

Rosmarinic acid (RA) is a natural compound that is gaining wide popularity owing to its broad-spectrum biological activities. RA is known for its wide range of medicinal properties and therapeutic applications in a vast range of neurodegenerative disorders thus making it a vital natural compound. Human transferrin (hTf) is a clinically significant protein that plays a pivotal role in maintaining iron homeostasis. The importance of studies pertaining to hTf is attributable to the pivotal role of iron deposition in CNS in neurodegenerative disorders. The study was intended to have an insight into the interaction between RA and hTf employing multispectroscopic approach, molecular docking, and molecular dynamic simulation studies. Fluorescence quenching studies revealed that RA shows an excellent binding affinity to hTf with a binding constant (K) of 107 M-1 and is guided by static mode of quenching. Isothermal titration calorimetry (ITC) further validated the spontaneous nature of binding. The estimation of enthalpy change (∆H) and entropy change (∆S) suggested that the RA-hTf complex formation is driven by hydrogen bonding, thereby making this process seemingly specific. Further, Fourier transform infrared (FTIR) and circular dichroism (CD) spectra suggested that RA induces conformational and structural changes in hTf. Additionally, molecular dynamics (MD) studies were carried out to investigate the stability of the hTf and hTf-RA system and suggested that binding of RA induces structural alteration in hTf with free hTf being more stable. This study provides a rationale to use RA in drug development against neurodegenerative disorders by designing novel functional foods containing RA.

Rosmarinic Acid Exhibits Anticancer Effects via MARK4 Inhibition

Microtubule affinity regulating kinase (MARK4) is a potential drug target for different types of cancer as it controls the early step of cell division. In this study, we have screened a series of natural compounds and finally identified rosmarinic acid (RA) as a potential inhibitor of MARK4. Molecular docking and 500 ns all-atom simulation studies suggested that RA binds to the active site pocket of MARK4, forming enough number of non-covalent interactions with critical residues and MARK4-RA complex is stable throughout the simulation trajectory. RA shows an excellent binding affinity to the MARK4 with a binding constant (K) of 107 M-1. Furthermore, RA significantly inhibits MARK4 activity (IC50 = 6.204 µM). The evaluation of enthalpy change (∆H) and entropy change (∆S) suggested that the MARK4-RA complex formation is driven by hydrogen bonding and thus complexation process is seemingly specific. The consequence of MARK4 inhibition by RA was further evaluated by cell-based tau-phosphorylation studies, which suggested that RA inhibited the phosphorylation of tau. The treatment of cancer cells with RA significantly controls cell growth and subsequently induces apoptosis. Our study provides a rationale for the therapeutic evaluation of RA and RA-based inhibitors in MARK4 associated cancers and other diseases.

Structural and biochemical investigation of MARK4 inhibitory potential of cholic acid: Towards therapeutic implications in neurodegenerative diseases

Microtubule affinity regulating kinase (MARK4) is considered as a potential drug target for diabetes, cancer, and neurodegenerative diseases. Since the role of MARK4 in the phosphorylation of tau protein and subsequently Alzheimer's disease has been established, therefore, we have investigated the binding affinity and MARK4 inhibitory potential of cholic acid (CHA) using both computational and spectroscopic methods. Molecular docking suggested a strong binding of CHA to the functionally important residues of MARK4. We further performed 500 ns molecular dynamics simulation which suggested the MARK4-CHA system was quite stable throughout the simulation trajectory. CHA potential binds to the MARK4 with a binding constant (K) of 10⁷ M^-1 at 288 K. Further, MARK4 activity was inhibited by CHA with an IC₅₀ = 5.5 μM. Further insights into the thermodynamic parameters suggested that MARK4-CHA complex formation is driven by both electrostatic and van der Waals interactions. Overall study provides a rationale to use CHA in the drug development via MARK4 inhibition, towards possible therapeutic implications in neurodegenerative diseases.