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Ovalbumin (OVA), the major component of egg white, has been used as a model carrier protein to study the interaction of four bioactive phytochemicals 6‐hydroxyflavone, chrysin, naringin, and naringenin. A static quenching mechanism was primarily associated with the complexation of the flavonoids with OVA. Hydrophobic forces play a major part in the stability of the complexes. The structural changes within the protein in response to flavonoid binding revealed a decrease in OVA's α‐helical content. The hypothesized binding site for flavonoids in OVA overlaps with one or more immunoglobulin E‐binding epitopes that may have some effect in the immunoglobulin E response pathway. The flavonoids remain in the same binding site throughout the simulation time and impart protein stability by forming different noncovalent interactions. This study presents comprehensive information about the interaction of the flavonoids with OVA and the associated structural variations after the binding, which might help researchers better comprehend similar medication pharmacodynamics and provide critical information for future therapeutic development. [ABSTRACT FROM AUTHOR]

The fluorescence emission behavior of bioactive dietary polyphenols in serum albumin has been explored in order to understand their spectroscopic properties along with their binding characteristics using multi-spectroscopic and molecular docking studies. The dual emission character of kaempferol (KMP) within the serum albumin environment suggests that it can be used as a multi-wavelength fluorescent probe. [ABSTRACT FROM AUTHOR]

The interactions of bio-active flavonoids, 7-hydroxyflavone (7HF) and 3-hydroxyflavone (3HF) with hen egg white lysozyme (HEWL) have been established using differential spectroscopic techniques along with the help of molecular docking method. The characteristic dual fluorescence of 3HF due to the excited intramolecular state proton transfer (ESIPT) process is altered markedly upon binding with HEWL. Both the flavonoids quenched the intrinsic fluorescence of HEWL through static quenching mechanism while the binding affinity of 7HF was found to be greater than 3HF under experimental conditions. The binding constant ( K b ) values were estimated to be in the order of 10 4  M −1 and decreased with the rise in temperature. The contributions of the thermodynamic parameters (Δ H ° and Δ S °) revealed that hydrophobic forces along with hydrogen bonding played a crucial role in the interaction of HEWL with 7HF and 3HF respectively and this finding was aptly supported by the molecular docking studies. The donor (HEWL) to acceptors (7HF and 3HF) binding distances were calculated using the Föster's theory. The phenomena of blue shifting of the emission maxima of the residues indicated the increase in hydrophobicity around the Trp micro-environment upon addition of the flavonoids was observed from synchronous and 3D fluorescence measurements whereas REES study indicated the decrease in mobility of the Trp residues upon addition of the ligands. The CD, FTIR and thermal melting studies indicated the alteration in the structural stability of HEWL on ligand binding and it was found that the % α-helical content decreased on complexation with 7HF and 3HF respectively as compared to native state. The flavonoids were found to inhibit the enzymatic activity of HEWL. The molecular docking results and accessible surface area ( ASA ) calculations revealed that the flavonoids bind within the active site of HEWL. The negative Δ G ° values obtained from experimental and molecular docking studies indicate the spontaneity of the interaction processes. [ABSTRACT FROM AUTHOR]

• A novel indene-phloroglucinol tethered compound IPC1 containing indene and phloroglucinol has been synthesized. • The binding interaction of compound IPC1 with HSA was determined. • Compound IPC1 quenched the intrinsic fluorescence of HSA by unusual static quenching. • Binding was found to be entropically driven and assisted by hydrophobic forces. • No major changes in the helical stability of HSA were observed upon interaction. A new indene-phloroglucinol tethered compound IPC1 was synthesized in our laboratory in three steps. The interaction of the final compound IPC1 with human serum albumin (HSA) was studied using multi-spectroscopic and molecular docking methods. UV–vis and fluorescence studies confirmed the spontaneous formation of ground state complex and the values of the binding constants were found to be in the order of 104 M−1 (4.727×104 M−1 at 290.15 K). Positive Δ S ° (+112.797 J K−1 mol−1) and Δ H ° (+6.756 KJ mol−1) indicate the involvement of hydrophobic interaction as the major contributing force in the complex formation process. Site marker studies suggested that the compound IPC1 binds near the subdomain IIIA of HSA, which was further supported by fluorescence spectroscopic and molecular docking analysis. A novel indene-phloroglucinol tethered compound IPC1 containing indene and phloroglucinol has been synthesized and binding interaction with the carrier protein, HSA has been explored using multi-spectroscopic and molecular docking studies. Binding force was found to be entropically driven and assisted by hydrophobic forces with no major structural variations. [Display omitted] [ABSTRACT FROM AUTHOR]

DNA is essential in biological processes as it directs transcription and translation assisting in RNA and protein synthesis. Extended periods of elevated blood glucose levels cause non-enzymatic DNA glycation, which results in the formation of DNA-AGEs and the production of free radicals, causing structural perturbation of DNA. In this work, we have investigated the glycation of calf thymus (ct-DNA) DNA and examined its inhibition by two anthraquinone derivatives, purpurin and aloin. Ribose sugar served as the glycating agent inducing non-enzymatic glycation of DNA and subsequent DNA-AGEs formation. UV–vis and fluorescence spectroscopic methods were utilized to characterize DNA-AGE formation in vitro. Circular dichroism (CD) spectroscopy was used to observe the structural disruption of DNA caused by glycation. The changes in AGEs fluorescence intensity and melting temperature (T m) were measured to assess the inhibition of glycation process by aloin and purpurin. These derivatives demonstrated inhibitory effects via binding to glycating sites of ct-DNA or by scavenging free radicals generated during glycation. The current study elucidates the inhibitory actions of aloin and purpurin on DNA glycation, suggesting their possible applications in mitigating the adverse consequences linked to increased ribose concentrations. [Display omitted] • Structural/conformational changes of DNA due to glycation were confirmed by circular dichroism (CD) studies. • Docking studies revealed that aloin and purpurin interact with guanine, adenine, and cytosine bases of DNA. • Aloin and purpurin bind to the double-stranded DNA through groove binding mode. • Aloin and purpurin inhibited the formation of DNA-advanced glycation end products (DNA-AGEs). • Ligands inhibited the glycation process in DNA by binding to its glycation sites and/orpartly due to their antioxidant properties. [ABSTRACT FROM AUTHOR]

The interactions of naringenin (NG) and naringin (NR) with Hen Egg White Lysozyme (HEWL) in aqueous medium have been investigated using UV–vis spectroscopy, steady-state fluorescence, circular dichroism (CD), Fourier Transform infrared spectroscopy (FT-IR) and molecular docking analyses. Both NG and NR can quench the intrinsic fluorescence of HEWL via static quenching mechanism. At 300 K, the value of binding constant ( K b ) of HEWL-NG complex (5.596 ± 0.063 × 10 4 M − 1 ) was found to be greater than that of HEWL-NR complex (3.404 ± 0.407 × 10 4 M − 1 ). The negative Δ G ° values in cases of both the complexes specify the spontaneous binding. The binding distance between the donor (HEWL) and acceptor (NG/NR) was estimated using the Försters theory and the possibility of non-radiative energy transfer from HEWL to NG/NR was observed. The presence of metal ions (Ca 2 + , Cu 2 + and Fe 2 + ) decreased the binding affinity of NG/NR towards HEWL. Synchronous fluorescence studies indicate the change in Trp micro-environment due to the incorporation of NG/NR into HEWL. CD and FT-IR studies indicated that the α-helicity of the HEWL was slightly enhanced due to ligand binding. NG and NR inhibited the enzymatic activity of HEWL and exhibited their affinity for the active site of HEWL. Molecular docking studies revealed that both NG and NR bind in the close vicinity of Trp 62 and Trp 63 residues which is vital for the catalytic activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Binding of coumarin derivatives with bovine hemoglobin have been investigated using biophysical techniques. • Static quenching mechanism is involved in the binding interactions of coumarins with bovine hemoglobin. • Binding constant was found moderate in nature. • Secondary structure of the protein was perturbed during ligand binding. • Results from computational studies correlated well with the experimental findings. Biological functioning takes place through the interaction of biomacromolecules with each other or with other small molecules. The molecular recognition of a carrier protein, bovine hemoglobin (BHb), with 7-hydroxycoumarin (7-HC) and 4-methyl-7-hydroxycoumarin (4-Me-7-HC) was investigated using various biophysical and computational techniques. Fluorescence spectroscopy and molecular docking revealed the interaction of 7-HC and 4-Me-7-HC with β 2 -Trp37 fluorophore, quenching the intrinsic fluorescence of BHb. The mechanism of quenching was determined to be static. The binding constant (K b) for BHb with 7-HC and 4-Me-7-HC was found to be 6.15 × 104 M−1 and 5.73 × 104 M−1 at 298 K, respectively. This moderate form of protein–ligand association could result in reversible binding to transport and release the ligand in the target tissue. Negative Δ G for both complexes suggested spontaneous binding. Positive Δ H and Δ S for BHb-7-HC indicated hydrophobic forces played a dominant role in binding. However, hydrogen bonding and hydrophobic forces dictated the binding process for BHb-4-Me-7-HC due to obtaining negative Δ H and positive Δ S values. Changes in the microenvironment of the binding site were observed through 3D fluorescence studies. Through Förster resonance energy transfer (FRET), a binding distance of less than 7 nm was measured between BHb and 7-HC/4-Me-7-HC. The interaction of coumarin derivatives with BHb resulted in a loss of α-helical content of the protein, as proven by circular dichroism (CD) and Fourier transform infrared (FTIR) measurements. Molecular dynamic simulations showed the binding of 7-HC supplemented the stability of BHb, whereas 4-Me-7-HC binding resulted in conformational changes in the structure of BHb. [ABSTRACT FROM AUTHOR]

Human serum albumin (HSA), an abundant protein in human plasma, which is associated with the transportation of numerous drugs, fatty acids to their targets and regulates the blood pH levels, is exposed to non-enzymatic glycation by reducing sugars. The existence of elevated levels of glucose during diabetes mellitus mediates the glycation of HSA which leads to structural and functional modification of the protein. The aim of our present study is to determine the effect of non-enzymatic glycation on the binding of a bioactive flavonoid luteolin to HSA using multi-spectroscopic and computational studies. The intrinsic fluorescence exhibited by the proteins (HSA and gHSA) were quenched by luteolin through static quenching mechanism. The binding constant for the interaction of HSA with luteolin was found higher as compared to that of gHSA-Luteolin at the experimental temperatures (290, 300 and 310 K). The ∆ G values for the complexes formed between HSA/gHSA and luteolin were observed to be negative, indicating the spontaneity of the binding processes. Both enthalpy and entropy factors contribute to the binding of luteolin to HSA, whereas, enthalpy factors played a major role in the binding of luteolin to gHSA. A reduction in the α-helical content of HSA-Luteolin complex was observed, but no significant change was found for gHSA-Luteolin complex. Site probe displacement and related binding studies indicated that luteolin binds to both Subdomain IIA and IIIA of HSA and gHSA but with different affinities. Further molecular docking and MD simulation studies confirmed that luteolin preferably binds to the Subdomain IIA of HSA and IIIA of gHSA. These information, in turn, would give a better understanding of the functional changes occurred due to structural modification of HSA induced by glycation and may have some useful impact on the field of pharmaceutical sciences. Unlabelled Image • Luteolin was found to quench the intrinsic fluorescence emission of HSA and gHSA. • A lower binding affinity of luteolin was observed for gHSA as compared to HSA. • Binding of luteolin induces structural changes in HSA, but not significantly in gHSA. • Luteolin binds preferably to the subdomain IIA of HSA and IIIA of gHSA respectively. [ABSTRACT FROM AUTHOR]

In recent years research based on kaempferol (KMP) has shown its potential therapeutic applications in medicinal chemistry and clinical biology. Therefore, to understand its molecular recognition mechanism, we studied its interactions with the carrier proteins, namely, human serum albumin (HSA), bovine hemoglobin (BHb) and hen egg white lysozyme (HEWL). The ligand, KMP was able to quench the intrinsic fluorescence of these three proteins efficiently through static quenching mode. The binding constant (K b) for the interactions of KMP with these three proteins were found in the following order: HSA-KMP > BHb-KMP > HEWL-KMP. Different non-covalent forces such as hydrogen bonding and hydrophobic forces played a major role in the binding of KMP with HSA and HEWL, whereas hydrogen bonding and van der Waals forces contribute to the complexation of BHb with KMP. KMP was able to alter the micro-environment near the Trp fluorophore of the proteins. KMP altered the secondary structural component of all three proteins. The putative binding sites and the residues surrounding the KMP molecule within the respective protein matrix were determined through molecular docking and molecular dynamics (MD) simulation studies. The conformational flexibility of the ligand KMP and the three individual proteins were also evident from the MD simulation studies. Unlabelled Image • Kaempferol (KMP) quenched the intrinsic fluorescence of HSA, BHb, and HEWL. • Non-covalent forces played significant roles in the complexation processes. • Micro-environment around the tryptophan of the proteins altered on complexation with KMP. • The alterations in the α-helical content of HEWL and BHb was observed on binding with KMP. • Docking and MD simulation studies indicate the preferred binding locations of KMP within the proteins. [ABSTRACT FROM AUTHOR]