Spectroscopic studies on the interaction of Ga3+-hypocrellin A with myoglobin

PROTEIN BINDING CHARACTERISTICS OF YOHIMBINE, A NATURAL INDOLE ALKALOID BASED DRUG FOR ERECTILE DYSFUNCTION

Even to this day, talking about sexual-dysfunctions largely remains a taboo. Hence less studies were recorded and fewer remedies given. Erectile dysfunction (ED) is one of the most commonly treated psychological disorders which leads to major distress, interpersonal limitation and reduces the quality of life & marriage. This study aimed to assess a plant-derived molecule, Yohimbine (Yoh, a β-carboline indole-alkaloid; often used for ED treatment) and its potential binding phenomenon with hemoglobin (Hb). Successful binding of the Yoh with Hb is evident from spectroscopic and molecular-docking results. Yoh quenched the fluorescence of Hb efficiently through static mode. The binding affinity was in the order of 10⁵ M^-1 with 1:1 stoichiometry. Thermodynamic analyses concluded that the protein-ligand association to be spontaneous and attributed by entropy-driven exothermic-binding. Non-polyelectrolytic factor was the core, dominating factor. The structural aspects have been deciphered through infra-red spectroscopy and computational-methods. The giant 3D-protein moiety was significantly perturbed through drug-binding. Hydrophobic forces and hydrogen bonding participation were stipulated by molecular modeling data. This study reveals the detailed interaction pattern and molecular mechanism of Hb-Yoh binding; correlating the structure-function relationship for the first time; therefore, holds enormous importance from the standpoint of rational and efficient drug-designing & development.

"Rigid" structure is a key determinant for the low digestibility of myoglobin

Myoglobin, a critical protein responsible for meat color, has been shown insusceptible to digestion. The underlying mechanism is not clear. The present study aimed to evaluate whether the structural properties of myoglobin are associated with its insusceptibility to digestion using spectroscopic and computational techniques. Myoglobin was degraded by only 7.03% by pepsin and 33.00% by pancreatin. The structure of myoglobin still maintained α-helix after the two-step digestion, with the exposure of some aromatic residues. In addition, molecular dynamics modeling suggested that hydrophobic amino acid residues (Phe 111, Leu 10, Ala 115, Pro 116) in pepsin and polar amino acid residues (Tyr 146, Thr 95) in myoglobin were found in the proximity of binding sites, which could result in the low digestibility of myoglobin. Our findings provide a new insight into the underlying mechanisms on the difficulty in digestion of myoglobin.

Structural dynamics studies on the binding of aflatoxin B1 to chicken egg albumin using spectroscopic techniques and molecular docking

Aflatoxin B₁, a mycotoxin produced by large number of Aspergillus species including Aspergillus flavus and Aspergillus parasiticus, has been described as the most potent carcinogenic mycotoxin. In this study, we have used a multiple spectroscopic and molecular docking approach to investigate the interaction of aflatoxin B₁ (AFB₁) with chicken egg albumin (CEA). Fluorescence spectroscopy, UV-Vis spectroscopy, and three-dimensional fluorescence spectroscopic techniques were employed to gain insight into the conformational changes in CEA in the presence of AFB₁. Fluorescence spectroscopy revealed ligand-induced quenching in the fluorescence emission spectra of CEA upon binding with AFB₁. Hyperchromic effect was observed in case of the ground state complex formation between CEA and AFB₁ by UV-Vis spectroscopy. To gain further comprehension into the site of binding of AFB₁ to CEA, competitive site marker displacement assay was performed using warfarin site marker. The magnitude of ΔG value calculated from fluorescence-based method was negative which confirmed spontaneous process. The results obtained suggest that the binding is enthalpy driven and van der Waals force and hydrogen bonds are stabilizing the AFB₁-CEA complex. Three-dimensional fluorescence studies also confirmed the quenching in the fluorescence intensity around tryptophan residues in CEA. Circular dichroism assessment revealed reduction in the alpha helical content of CEA in the presence of AFB₁. Molecular docking studies showed hydrophobic interaction, van der Waals forces, and hydrogen bonds as major forces present in interaction between CEA and AFB₁. The overall study confirms conformational and structural alteration in the protein due to binding of AFB₁.Communicated by Ramaswamy H. Sarma.

Interaction of cyanidin-3-O-glucoside with three proteins

We studied the binding of cyanidin-3-O-glucoside (C3G) with bovine serum albumin (BSA), hemoglobin (Hb) and myoglobin (Mb), using multi-spectral techniques and molecular modeling. Fluorescence and time-resolved fluorescence studies suggested that C3G quenched BSA, Hb or Mb fluorescence in a static mode with binding constants of 4.159, 0.695 and 1.545 × 10(4) L mol(-1) at 308K, respectively. The thermodynamic parameters represented hydrogen bonds and van der Waals forces dominated the binding. Furthermore, CD, UV-vis, and three-dimensional fluorescence spectra results indicated the secondary structures of BSA, Hb and Mb were partially destroyed by C3G with the α-helix percentage of C3G-Hb and C3G-Mb decreased while that of C3G-BSA was increased. UV-vis spectral results showed these binding interactions partially affected the heme bands of Hb and Mb. In addition, molecular modeling analysis supported the experimental results well. The calculated results of equilibrium fraction showed that the concentration of free C3G in plasma was high enough to be stored and transported from the circulatory system to reach their target sites to provide their therapeutic effects.