Data in support of intermolecular interactions at early stage of protein/detergent particle association induced by salt/polyethylene glycol mixtures

The data provide information in support of the research article, “Intermolecular interactions at early stage of protein/detergent particle association induced by salt/polyethylene glycol mixtures” [1]. The data regarding variation of absorption spectra is used as an indicator of the duration of Rp. viridis PRU and RC, Rb. sphaeroides RC and LH2, and Rb. capsulatus LH2 in the native state in the presence of NaCl/polyethylene glycol (PEG) mixture. The data about minimum concentrations of salt and PEG whose aqueous phases are mutually separated presents information on additional influence of Tris buffer and N-octyl-β-d-glucoside on the salt–PEG phase separation.


a b s t r a c t
The data provide information in support of the research article, "Intermolecular interactions at early stage of protein/detergent particle association induced by salt/polyethylene glycol mixtures" [1]. The data regarding variation of absorption spectra is used as an indicator of the duration of Rp. viridis PRU and RC, Rb. sphaeroides RC and LH2, and Rb. capsulatus LH2 in the native state in the presence of NaCl/polyethylene glycol (PEG) mixture. The data about minimum concentrations of salt and PEG whose aqueous phases are mutually separated presents information on additional influence of Tris buffer and N-octyl-β-D-glucoside on the salt-PEG phase separation. Wild-type photosynthetic bacteria were obtained from ATCC. Chemicals employed were high-grade ones; polyethylene glycol 4000 for gas chromatography was purchased from MERCK, NaCl and Tris(hydroxymethyl)aminomethane for biochemical assay from Wako, N-octyl-β-D-glucoside and N-dodecyl-β-D-maltoside from DOJINDO, and N,N-dimethyldodecylamine N-oxide from SIGMA Experimental features Absorption spectra were measured at various time points after NaCl/PEG mixture addition. Minimum concentrations for immiscible aqueous phases of salt and PEG were determined in the presence of 25 mM Tris buffer and 8 mg/mL OG.

Data source location
Tsukuba, Japan

Data accessibility
Data are available in this article.

Value of the data
Protein stability is a significant factor for determination of measurement time points after precipitant addition in the study of association of proteins in the native states.
Protein stability will also provide basic information for the study of denaturation process of proteins caused by salt/PEG mixtures.
Influence of buffer and detergent on salt-PEG phase separation is basic information to avoid the undesired influence on the association of integral membrane proteins.

Data
In this data article, data are shared regarding protein stability and salt-polyethylene glycol (PEG) phase separation. The former is absorption spectra of Rp. viridis PRU [2,3] and RC, Rb. sphaeroides RC [4,5] and LH2, and Rb. capsulatus LH2 measured at different time points after addition of NaCl/PEG mixture. The latter is shown as minimum concentrations of salts and PEG that form immiscible aqueous phases [6] in the presence of 25 mM Tris buffer and 8 mg/mL N-octyl-β-D-glucoside.

Experimental design, materials and methods
2.1. Stability of integral membrane proteins in the presence of NaCl/polyethylene glycol mixture Fig. 1 shows representatives of the spectra measured at various time points after the addition of NaCl/ PEG mixture. At one hour or shorter time points after the mixture addition, no variations in the spectra were observed for all the proteins. After several to 30 days, however, four proteins excluding Rb. sphaeroides RC exhibited variation in their absorption spectra that reflected variation of the intramolecular cofactors and the peptides supporting them. With Rp. viridis PRU, the absorption band with a maximum at 1006 nm, arising from bacteriochlorophyll in the LH1 subunits, decreased and a new peak appeared at 687 nm. In the spectra of Rp. viridis RC, the absorption band with a maximum at 830 nm, arising from special pair of bacteriochlorophyll, disappeared. With Rb. sphaeroides LH2 and Rb. capsulatus LH2, the two absorption peaks at 800 nm and 850 nm decreased and a small peak appeared at 690 nm.

Influence of Tris buffer and N-octyl-β-D-glucoside on phase separation of salt and polyethylene glycol
Minimum PEG concentrations for phase separation at various salt concentrations were determined in the presence of 25 mM Tris buffer and 8 mg/mL OG, as follows. A concentrated salt solution, a 625 mg/mL PEG solution, a 400 mM Tris-HCl solution (pH 8.0), a 200 mg/mL OG solution and pure water were put in small glass tubes at different ratios, and the mixture was shaken vigorously on a vortex mixer. Formation of mutually immiscible phases was judged by observing with eyes whether the resultant mixtures were turbid. The result is shown in Fig. 2