Modulation of Prototropic Activity and Rotational Relaxation Dynamics of a Cationic Biological Photosensitizer within the Motionally Constrained Bio-environment of a Protein

Abstract

The present work describes the interaction of a promising cancer cell photosensitizer, harmane (HM), with a model transport protein, Bovine Serum Albumin (BSA). The studied molecule of interest (HM) belongs to the family of naturally occurring fluorescent drug-binding alkaloids, the β-carbolines. A combined use of steady-state and time-resolved fluorescence techniques is applied to follow and characterize the binding interaction. The polarity-dependent prototropic activity of HM is found to be responsible for the commendable sensitivity of the probe to the protein environments and is distinctly reflected on the emission profile. Steady-state fluorescence anisotropy study reveals the impartation of a considerable degree of motional restriction on the drug molecule as a result of binding to the protein. Contrary to the single-exponential nature of fluorescence anisotropy decay of HM in aqueous buffer, they are found to be biexponential in the protein environment. The rotational relaxation dynamics of HM within the protein has been interpreted on the lexicon of the Two-Step and Wobbling-in-Cone model. The probable binding location for the cationic drug is found to be the hydrophilic binding zone of BSA, i.e., domain I (characterized by a net negative charge). The AutoDock-based blind docking simulation has been explored for evaluating an unbiased result of the probable interaction site of HM in the protein. To unfold the effect of binding of the drug on the secondary structural content of the protein, circular dichroism (CD) spectroscopy has been exploited to see that binding of the drug accompanies some decrease in α-helical content of BSA, and the effect gradually saturates toward a higher drug/protein molar ratio.

Esterase activity and conformational changes of bovine serum albumin toward interaction with mephedrone: Spectroscopic and computational studies

“…Generally, the esterase‐like activity of albumins decreases if the binding of the ligand induces conformational change in a way, where catalytic amino acid residues of the proteins (Tyr‐411, Arg 410, Lys‐413, and Lys‐414) are less accessible to the substrate; however, the esterase‐like activity increases if the binding of the ligand makes these residues more accessible to the substrate . It was shown that on increasing the concentration of 4MMC, K m gets altered, while V max remains almost unchanged at all concentration studies, suggesting that 4MMC interacts with the same catalytic part of BSA . This indicates that 4MMC binds with near active site of BSA where substrate usually occupies.…”

“…Figure shows the far‐UV CD spectra of native BSA (2 μM) and BSA in presence of 4MMC (100 μM). The native BSA shows 2 negative peaks at 208 and 222 nm, which is a characteristic of the α ‐helix secondary structure . The CD signal of BSA decreases on the addition of 4MMC, indicating that 4MMC induced the conformational change in the secondary structure of the BSA.…”

Insights into the Binding of 3-(1-Phenylsulfonyl-2-methylindol-3-ylcarbonyl) Propanoic Acid to Bovine Serum Albumin: Spectroscopy and Molecular Modelling Studies

“…According to the Forster dipole-dipole non-radiative energy transfer theory energy transfer is to happen the following conditions [18,19]. (1) The donor (emit fluorescence) should have more fluorescence quantum yield, (2) Overlap (>30%) of the fluorescence emission spectrum of the donor with the absorption spectrum of the acceptor.…”

Quenching interaction of BSA with DTAB is dynamic in nature: A spectroscopic insight

“…From the figure it is pretty evident that the CD spectra of BSA alone has two minima at 208 and 222 nm, which is a clear signature of the existence of ␣-helix present in the protein [19]. From the obtained ellipticity we first transformed it to Mean Residual Ellipticity (MRE) at 222 nm (please see SI for details) [36]. To establish this change brought in by the added surfactant, we plotted the MRE values at 222 nm against [DTAB] (Figure 6b).…”