Data for β-lactoglobulin conformational analysis after (-)-epigallocatechin gallate and metal ions binding.

This data article contains complementary results related to the paper "Effect of metal ions on the binding reaction of (-)-epigallocatechin gallate to β-lactoglobulin" (Zhang et al., 2017) [1]. Data was obtained by circular dichroism (CD) spectroscopy to investigate potential β-lactoglobulin (β-Lg) conformational changes with different concentrations of EGCg and Cu2+ or Al3+ added to β-Lg. 500 µL of the 25 µM β-Lg solution containing EGCg (25 µM) or metal ions (0-500 µM) were measured, and the spectra were recorded. CD spectroscopy data present in this article indicated that the β-Lg-Cu, β-Lg-Al and β-Lg-EGCg interaction resulted in unfolding of the secondary structure of β-Lg.

Specifications Table

Value of the data

The data provides some additional data on the effects of metal ions on the binding reaction of EGCg to β-Lg.

The data indicated the conformational change of β-Lg after binding with EGCg or metal ions Cu, Al.

The interaction between [β-Lg-Cu] and [β-Lg-Al] results in unfolding of the secondary structure of β-Lg.

This data provide insights in understanding the effects of metal ions on the binding reaction of polyphenol compounds to β-Lg.

Data

Fig. 1 reports the CD spectra of β-Lg with different concentrations of EGCg or Cu2+ or Al3+. The negative bands at 222 nm could indicate the α-helix structure of the proteins [1,3].

Fig. 1

(A) CD spectra of β-Lg-EGCg system. a, (25 µM β-Lg), b (25 µM EGCg); (B) CD spectra of β-Lg-Cu system. a, (25 µM β-Lg), c(Cu2+): a (0), b (100 µM), c (200 µM), d (300 µM), e (400 µM), f (500 µM); (C) CD spectra of β-Lg-Al system. a (25 µM β-Lg), c(Al3+): a (0), b (100 µM), c (200 µM), d (300 µM), e (400 µM).

Experimental design, materials and methods

Materials

EGCg (≥95%) and β-Lg (A variant, purity ≥90%) were purchased from Sigma-Aldrich Co. (St. Louis, MO, USA). Working solutions of EGCg (0.25 mM) were prepared by dissolving the EGCg in a 50% methanol solution. The working solution of β-Lg (25 µM) was prepared in 20 mM PBS buffer, pH 7.4 and stored in a refrigerator prior to use. The β-Lg and EGCg concentrations were determined spectrophotometrically by their extinction coefficients: ε280(β-Lg)=17600 M−1 cm−1 and ε280(EGCg)=9700 M−1 cm−1 at 280 nm [4], [5]. For in vitro experiments, the working solutions of Cu2+ and Al3+ (1.0 mM) were prepared by dissolving CuCl2·2H2O and AlCl3, respectively, in double-distilled water containing 0.1 M HCl to facilitate dissolution. All other reagents and solvents were of analytical reagent grade and used without further purification. All aqueous solutions were prepared using freshly double-distilled water.

Experimental design

CD spectroscopy was performed using a MOS-500 spectropolarimeter (Bio-Logic, France) with the modified method of Li et al. [2]. The CD spectra of the β-Lg, [β-Lg-EGCg] and [β-Lg-metal] systems were recorded between 190 and 250 nm by scanning the spectrum at 25 °C, with a scanning speed of 100 nm min−1, 2 s response time, and 1.0 nm step size. All samples were prepared in 20 mM PBS buffer at pH 7.4. To investigate the effect of EGCg, Cu2+ and Al3+ on the secondary structure of β-Lg, 500 µL of the 25 µM β-Lg solution containing EGCg (25 µM) or metal ions (0–500 µM) were measured, and the spectra were recorded. The samples were loaded into a rectangular quartz cuvette with a path length of 1 mm. The spectra of three consecutive scans were averaged and corrected by subtracting the solvent/buffer spectra.

Subject area	Chemistry
More specific subject area	Polyphenol chemistry
Type of data	Figure
How data was acquired	MOS-500 spectropolarimeter (Bio-Logic, France)
Data format	Analyzed
Experimental factors	CD spectroscopy was performed with the method of Li et al. [2].
Experimental features	All samples were prepared in 20 mM PBS buffer at pH 7.4. 500 µL of the 25 µM β-Lg solution containing EGCg (25 µM) or metal ions (0–500 µM) were measured, and the spectra were recorded.
Data source location	Nanjing, China
Data accessibility	Data is with this article