A study on photochemical behavior of lysozyme-bromophenol blue complex and its analytical application

Lysozyme crystals dyed with bromophenol blue: where has the dye gone?

Protein crystals can easily be coloured by adding dyes to their mother liquor, but most structures of these protein-dye complexes remain unsolved. Here, structures of lysozyme in complex with bromophenol blue obtained by soaking orthorhombic and tetragonal crystals in a saturated solution of the dye at different pH values from 5.0 to 7.5 are reported. Two different binding sites can be found in the lysozyme-bromophenol blue crystals: binding site I is located near the amino- and carboxyl-termini, while binding site II is located adjacent to helices α1 (residues 4-15) and α3 (residues 88-100). In the orthorhombic crystals soaked at pH 7.0, binding of the dye takes place in both sites without significant changes in the unit cell. However, soaking tetragonal crystals with bromophenol blue results in two different complexes. Crystals soaked at pH 5.5 (HEWL-T1) show a single dye molecule bound to site II, and the crystals belong to space group P4₃2₁2 without significant changes in the unit cell (a = b = 78.50, c = 37.34 Å). On the other hand, crystals soaked at pH 6.5 in the presence of imidazole (HEWL-T2) show up to eight molecules of the dye bound to site II, and display changes in space group (P2₁2₁2₁) and unit cell (a = 38.00, b = 76.65, c = 84.86 Å). In all of the structures, the dye molecules are placed at the surface of the protein near to positively charged residues accessible through the main solvent channels of the crystal. Differences in the arrangement of the dye molecules at the surface of the protein suggest that the binding is not specific and is mainly driven by electrostatic interactions.

Use of spectroscopic and zeta potential techniques to study the interaction between lysozyme and curcumin in the presence of silver nanoparticles at different sizes

This article describes, for the first time, the effect of three different sizes of silver nanoparticles on the binding of curcumin to lysozyme as examined by spectroscopic and zeta potential techniques at physiological conditions. The binding constants of curcumin to lysozyme in the presence of silver nanoparticles were measured. Based on the results of synchronous fluorescence and three-dimensional fluorescence spectroscopy, the presence of the different sizes of silver nanoparticles caused conformational changes in lysozyme during the binding of curcumin. Such changes were also observed when increasing the curcumin concentration. The results of fluorescence resonance energy transfer theory indicated that different sizes of silver nanoparticles could change the binding distance between curcumin and lysozyme. Based on the red edge excitation shift approach, we concluded that the limited mobility around the Trp residues decreased in the presence of silver nanoparticles with bigger size. Under resonance light scattering, the aggregation of curcumin on lysozyme in the presence of silver nanoparticles can play a major role in functional proteins. Communicated by Ramaswamy H. Sarma.

Role of Tryptophan in Protein–Nanocrystals Interaction: Energy or Charge Transfer

The understanding of the interaction between the semiconductor nanocrystals (NCs) and the proteins are essential for design and fabrication of nanocomposites for application in the field of biotechnology. Herein, we have studied the interaction between CdTe NCs and the proteins by steady-state and time-resolved photoluminescence (PL) spectroscopy. The steady-state PL intensity of CdTe NCs is quenched and enhanced in the presence of lysozyme and bovine serum albumin, respectively. However, the PL intensity of CdTe NCs is not affected with α-synuclein, indicating the role of tryptophan moiety in the protein–NCs interaction. The detailed analysis of PL data allows us to elucidate the dominant mechanism of interaction, i.e. charge or energy transfer, depending on the location of tryptophan residues in the protein. Assuming a Poisson statistic of lysozymes around NCs, the Poisson binding model is used to understand the kinetics of charge transfer from CdTe NCs to the lysozyme. It provides the average number of lysozymes present on the surface of one CdTe NC.