Multispectroscopic and Computational Analysis Insight into the Interaction of Cationic Diester-Bonded Gemini Surfactants with Serine Protease α-Chymotrypsin

Abstract

Accumulation of different protein-surfactant mixtures affords further knowledge about the structure-property interactions of biomacromolecules. They will help design suitable surfactants, which, in turn, can enhance the utilization of protein-surfactant complexes in biotechnologies, cosmetics, and food industry realms. Owing to their adaptable and remarkably notable properties, we are describing herein the interaction of C _m -E2O-C _m gemini surfactants (m = 12, 14, and 16) with α-CHT by employing various spectroscopic techniques including with molecular docking and density functional theory (DFT) method. Results have revealed complex formation, unfolding, and a static quenching mechanism in the interaction of gemini surfactants with α-CHT. The Stern-Volmer constant (K _SV), quenching constant (k _q), the number of binding sites (n), and binding constant (K _b) were interrogated by utilizing the fluorescence quenching method, UV-vis, synchronous, 3-D, and resonance Rayleigh scattering fluorescence studies. The data perceive the α-CHT-C _m -E2O-C _m complex formation along with conformational alterations induced in α-CHT. The contribution of aromatic residues to a nonpolar environment is illustrated by pyrene fluorescence. Fourier transform infrared spectroscopy and circular dichroism outcomes reveal conformational modifications in the secondary structure of α-CHT with the permutation of gemini surfactants. The computational calculations (molecular docking and DFT) further corroborate the complex formation between α-CHT and C _m -E2O-C _m gemini surfactants and the contribution of electrostatic/hydrophobic interaction forces therein.

Scheme 1. Chemical Structures of Cationic C_m-E2O-C_m Gemini Surfactants (m = (a) 12, (b) 14, and (c) 16) and (d) Crystallographic Structure of α-Chymotrypsin

Figure 1

UV–vis absorption spectra of α-CHT in the presence of C_m-E2O-C_m (m = (a) 12, (b) 14, and (c) 16) gemini surfactants (pH 7.8) at 298 K.

Figure 2

Synchronous fluorescence spectra of α-CHT (2 μM) with different concentrations of C_m-E2O-C_m (m = 12, 14, and 16) at (a–c) Δλ = 20 nm for Tyr and (d–f) Δλ = 60 nm for Trp at 298 K (pH 7.8).

Figure 3

Variation of micropolarity around pyrene as a function of C_m-E2O-C_m (m = (a) 12, (b) 14, and (c) 16) gemini surfactants at 298 K (pH 7.8).

Figure 4

FT-IR spectra of α-CHT (2 μM) in the absence and presence of 0.0867 mM C_m-E2O-C_m (m = 12, 14, and 16) gemini surfactants at 298 K (pH 7.8).

Figure 5

Three-dimensional (3-D) fluorescence spectra of (a) α-CHT (2 μM) in the absence and presence of 2.459 μM C_m-E2O-C_m (m = (b) 12, (c) 14, and (d) 16) gemini surfactants and (e) bar diagram at 298 K (pH 7.8).

Figure 6

CD spectra of α-CHT (40 μM) in the absence and presence of C_m-E2O-C_m (m = (a) 12, (b) 14, and (c) 16) gemini surfactants and (d) bar diagram at 298 K (pH 7.8).

Figure 7

Fluorescence emission spectra of α-CHT in the presence of C_m-E2O-C_m (m = (a) 12, (b) 14, and (c) 16) gemini surfactants at 298 K and pH 7.8.

Figure 8

Stern–Volmer plots for the binding of α-CHT with C_m-E2O-C_m (m = 12, 14, and 16) gemini surfactants at 298 K (pH 7.8).

Figure 9

Plots of log(F₀ – F)/F versus log[C_m-E2O-C_m] for quenching of α-CHT by C_m-E2O-C_m (m = 12, 14, and 16) gemini surfactants; [α-CHT] = 2 μM; [C_m-E2O-C_m] = 0.0049–0.0867 mM at 298 K and pH 7.8.

Figure 10

Docking pose of the α-CHT complexed with (a) C₁₂-E2O-C₁₂, (b) C₁₄-E2O-C₁₄, and (c) C₁₆-E2O-C₁₆ gemini surfactants.

Figure 11

Binding sites of α-CHT with (a) C₁₂-E2O-C₁₂, (b) C₁₄-E2O-C₁₄, and (c) C₁₆-E2O-C₁₆ gemini surfactants.

Figure 12

Electrostatic potential map representing the electrostatic potential strength of (a) gemini surfactant (C₁₂-E2O-C₁₂) and (b) Trp and (c) Tyr residues of α-CHT.

Figure 13

Optimized HOMO and LUMO configurations/energy gaps of the gemini surfactants and Trp and Tyr residues obtained via DFT calculations.