Atanu Singha Roy

Magnetic Field Effect Corroborated with Docking Study to Explore Photoinduced Electron Transfer in Drug-Protein Interaction

Conventional spectroscopic tools such as absorption, fluorescence, and circular dichroism spectroscopy used in the study of photoinduced drug-protein interactions can yield useful information about ground-state and excited-state phenomena. However, photoinduced electron transfer (PET) may be a possible phenomenon in the drug-protein interaction, which may go unnoticed if only conventional spectroscopic observations are taken into account. Laser flash photolysis coupled with an external magnetic field can be utilized to confirm the occurrence of PET and authenticate the spin states of the radicals/radical ions formed. In the study of interaction of the model protein human serum albumin (HSA) with acridine derivatives, acridine yellow (AY) and proflavin (PF(+)), conventional spectroscopic tools along with docking study have been used to decipher the binding mechanism, and laser flash photolysis technique with an associated magnetic field (MF) has been used to explore PET. The results of fluorescence study indicate that fluorescence resonance energy transfer takes place from the protein to the acridine-based drugs. Docking study unveils the crucial role of Ser 232 residue of HSA in explaining the differential behavior of the two drugs towards the model protein. Laser flash photolysis experiments help to identify the radicals/radical ions formed in the due course of PET (PF(•), AY(•-), TrpH(•+), Trp(•)), and the application of an external MF has been used to characterize their initial spin-state. Owing to its distance dependence, MF effect gives an idea about the proximity of the radicals/radical ions during interaction in the system and also helps to elucidate the reaction mechanisms. A prominent MF effect is observed in homogeneous buffer medium owing to the pseudoconfinement of the radicals/radical ions provided by the complex structure of the protein.

The influence of common metal ions on the interactions of the isoflavone genistein with bovine serum albumin.

The interaction of genistein with bovine serum albumin (BSA) has been characterized via UV-vis, fluorescence spectroscopy and Circular Dichroism (CD) measurements under physiological conditions. In this study, we have investigated the effect of some common metal ions on the binding of genistein with BSA using fluorescence studies. The fluorescence data reveal that the binding affinity of genistein to BSA increases in presence of certain metal ions. The possibility of non-radiative energy transition from the donor tryptophan to the acceptor genistein has been observed in absence and presence of metal ions. The observed similarities in the values of efficiency of energy transfer (E) and the separation between the donor and acceptor (r) in both the cases may be correlated with the complexation between the genistein and metal ions, which is also observed from the UV-vis studies. The changes in enthalpy (ΔH°) and entropy (ΔS°) of the interaction were found to be -14.64 kJ mol(-1) and +42.75 J mol(-1)K(-1) respectively. These values indicate the involvement of electrostatic interactions along with a hydrophobic association that results in a positive entropy change. CD analysis shows that there is a slight increase in the% α-helical content of BSA on binding with genistein at lower molar ratios. Warfarin and ibuprofen displacement studies in accordance with the molecular docking show that genistein binds to site I (subdomain IIA) of BSA.

Prolonged Glycation of Hen Egg White Lysozyme Generates Non Amyloidal Structures

Glycation causes severe damage to protein structure that could lead to amyloid formation in special cases. Here in this report, we have shown for the first time that hen egg white lysozyme (HEWL) does not undergo amyloid formation even after prolonged glycation in the presence of D-glucose, D-fructose and D-ribose. Cross-linked oligomers were formed in all the cases and ribose was found to be the most potent among the three sugars. Ribose mediated oligomers, however, exhibit Thioflavin T binding properties although microscopic images clearly show amorphous and globular morphology of the aggregates. Our study demonstrates that the structural damage of hen egg white lysozyme due to glycation generates unstructured aggregates.

An investigation into the altered binding mode of green tea polyphenols with human serum albumin on complexation with copper.

Green tea is rich in several polyphenols, such as (−)-epicatechin-3-gallate (ECG), (−)-epigallocatechin (EGC), and (−)-epigallocatechin-3-gallate (EGCG). The biological importance of these polyphenols led us to study the major polyphenol EGCG with human serum albumin (HSA) in an earlier study. In this report, we have compared the binding of ECG, EGC, and EGCG and the Cu(II) complexes of EGCG and ECG with HSA. We observe that the gallate moiety of the polyphenols plays a crucial role in determining the mode of interaction with HSA. The binding constants obtained for the different systems are 5.86 ± 0.72 × 104 M−1 (K ECG-HSA), 4.22 ± 0.15 × 104 M−1 (K ECG-Cu(II)-HSA), and 9.51 ± 0.31 × 104 M−1 (K EGCG-Cu(II)-HSA) at 293 K. Thermodynamic parameters thus obtained suggest that apart from an initial hydrophobic association, van der Waals interactions and hydrogen bonding are the major interactions which held together the polyphenols and HSA. However, thermodynamic parameters obtained from the interactions of the copper complexes with HSA are indicative of the involvement of the hydrophobic forces. Circular dichroism and the Fourier transform infrared spectroscopic measurements reveal changes in α-helical content of HSA after binding with the ligands. Data obtained by fluorescence spectroscopy, displacement experiments along with the docking studies suggested that the ligands bind to the residues located in site 1 (subdomains IIA), whereas EGC, that lacks the gallate moiety, binds to the other hydrophobic site 2 (subdomain IIIA) of the protein.

Study of the Interaction Between Fisetin and Human Serum Albumin: A Biophysical Approach

The binding of fisetin with human serum albumin (HSA) has been studied at different pH using UV-Vis, FTIR, CD and fluorescence spectroscopic techniques. The binding constants were found to increase with the rise in pH of the media. The negative ΔH° (kJ mol-1) and positive ΔS° (J mol-1 K-1) indicate that fisetin binds to HSA via electrostatic interactions with an initial hydrophobic association that result in a positive ΔS° . In presence of potassium chloride (KCl) the binding constants were found to be decrease. The α-helical content of HSA increased after binding with fisetin as analyzed from both CD and FTIR methods. The site marker displacement studies using fluorescence anisotropy suggest that fisetin binds to the hydrophobic pocket (Site 1, subdomain IIA) of HSA which is in good accordance with the molecular docking study. The change in accessible surface area (ASA) of residues of HSA was calculated to get a better insight into the binding.

A Comparative Study of Interaction of Tetracycline with Several Proteins Using Time Resolved Anisotropy, Phosphorescence, Docking and FRET

A comparative study of the interaction of an antibiotic Tetracycline hydrochloride (TC) with two albumins, Human serum albumin (HSA) and Bovine serum albumin (BSA) along with Escherichia Coli Alkaline Phosphatase (AP) has been presented exploiting the enhanced emission and anisotropy of the bound drug. The association constant at 298 K is found to be two orders of magnitude lower in BSA/HSA compared to that in AP with number of binding site being one in each case. Fluorescence resonance energy transfer (FRET) and molecular docking studies have been employed for the systems containing HSA and BSA to find out the particular tryptophan (Trp) residue and the other residues in the proteins involved in the binding process. Rotational correlation time (θc) of the bound TC obtained from time resolved anisotropy of TC in all the protein-TC complexes has been compared to understand the binding mechanism. Low temperature (77 K) phosphorescence (LTP) spectra of Trp residues in the free proteins (HSA/BSA) and in the complexes of HSA/BSA have been used to specify the role of Trp residues in FRET and in the binding process. The results have been compared with those obtained for the complex of AP with TC. The photophysical behaviour (viz., emission maximum, quantum yield, lifetime and θc) of TC in various protic and aprotic polar solvents has been determined to address the nature of the microenvironment of TC in the protein-drug complexes.

Interaction of multitryptophan protein with drug: an insight into the binding mechanism and the binding domain by time resolved emission, anisotropy, phosphorescence and docking.

The interaction of antibiotic Tetracycline hydrochloride (TC) with Alkaline Phosphatase (AP) from Escherichia coli, an important target enzyme in medicinal chemistry, having tryptophan (Trp) residues at 109, 220 and 268 has been studied using the steady state and time resolved emission of the protein and the enhanced emission of the bound drug. The association constant at 298 K (≈10(6) [M](-1)) and the number of binding site (=1) were estimated using the quenched Trp emission of AP, the enhanced emission and the anisotropy of the bound drug. The values of ΔH(0) and ΔS(0) are indicative of electrostatic and H-bonding interaction. The low temperature phosphorescence of free AP and the protein- drug complex and molecular docking comprehensively prove the specific involvement of partially exposed Trp 220 in the binding process without affecting Trp 109 and Trp 268. The Förster energy transfer (ET) efficiency and the rate constant from the Trp residue to TC=0.51 and ≈10(8) s(-1) respectively. Arg 199, Glu 219, Trp 220, Lys 223, Ala 231, Arg 232 and Tyr 234 residues are involved in the binding process. The motional restriction of TC imposed by nearby residues is reflected in the observed life time and the rotational correlation time of bound TC.

Complex formation of rutin and quercetin with copper alters the mode of inhibition of Ribonuclease A

Rutin and quercetin, both minor components of green tea and their Cu(II) complexes interact with Ribonuclease A (RNase A) in a novel way. The effects of rutin, quercetin and their copper complexes on the catalytic activity of the protein were investigated. Rutin shows an enhancement in the ribonucleolytic activity whereas the copper complexes and quercetin behave as non‐competitive type inhibitors with Ki values in the μM range. The secondary structural changes of RNase A in presence of the ligands were measured by circular dichroism and Fourier transform infrared spectroscopy. The binding parameters were obtained using a fluorescence quenching analysis.

Simple Crosstalk Model of Three Wires to Predict Nearend and Farend Crosstalk in an EMI/EMC Environment to Facilitate EMI/EMC Modeling

Electromagnetic coupling to cables has been a major source of EMC and EMI problems. In this paper, the methods of predicting the EM coupling and propagation in multiconductor transmission lines are presented. Crosstalk is an important aspect of the design of an electromagnetically compatible product. This essentially refers to the unintended electromagnetic coupling between wires and PCB lands that are in close proximity. Crosstalk is distinguished from antenna coupling in that it is a near field coupling problem. Crosstalk between wires in cables or between lands on PCBs concerns the intra-system interference performance of the product, that is, the source of the electromagnetic emission and the receptor of this emission are within the same system. With clock speeds and data transfer rates in digital computers steadily increasing, crosstalk between lands on PCBs is becoming a significant mechanism for interference in modern digital systems. To predict the crosstalk we designed a simple model of three conducting wires and took measurements for both nearend and farend crosstalk. Also the same model is being simulated by CST Microwave Studio (3D Electromagnetic Solver).

Preparation of albumin based nanoparticles for delivery of fisetin and evaluation of its cytotoxic activity

Fisetin is a well known flavonoid that shows several properties such as antioxidant, antiviral and anticancer activities. Its use in the pharmaceutical field is limited due to its poor aqueous solubility which results in poor bioavailability and poor permeability. The aim of our present study is to prepare fisetin loaded human serum albumin nanoparticles to improve its bioavailability. The nanoparticles were prepared by a desolvation method and characterized by spectroscopic and microscopic techniques. The particles were smooth and spherical in nature with an average size of 220 ± 8 nm. The encapsulation efficiency was found to be 84%. The in vitro release profile showed a biphasic pattern and the release rate increases with increase in ionic strength of solution. We have also confirmed the antioxidant activity of the prepared nanoparticles by a DPPH (2,2-diphenyl-1-picrylhydrazyl) assay. Further its anticancer activity was evaluated using MCF-7 breast cancer cell lines. Our findings suggest that fisetin loaded HSA nanoparticles could be used to transfer fisetin to target areas under specific conditions and thus may find use as a delivery vehicle for the flavonoid.