Chaperone potential of Pulicaria undulata extract in preventing aggregation of stressed proteins

Abstract

This study examined the effect of an aqueous extract of Pulicaria undulata on the 1,4-dithiothreitol (DTT)-induced aggregation of proteins. The effects of the chaperone properties of P. undulata extract on protein aggregation were determined by measuring light scattering absorption, fluorescence, and circular dichroism (CD) spectroscopy. The aqueous extract of P. undulata possesses good chaperone properties but the protection effect was varied in different protein. The extract showed a higher level of protection in high molecular weight proteins than in those of low molecular weight. Using a fluorescence study, the present study provides information on the hydrophobic area of proteins interacting with the P. undulata extract. In fact, by increasing the concentration of the P. undulata extract, the hydrophic area of the protein decreased. CD spectroscopy also revealed that DTT caused changes in both the tertiary and the secondary structure of the proteins, while in the presence of P. undulata extract, there was little change. Our finding suggests the possibility of using P. undulata extract for the inhibition of aggregation and the deposition of protein in disease.

Fig. 1

Visible absorption profiles at 340 nm of target protein aggregation in the presence or absence of different concentration of P. undulata extract for a insulin; b α-lactalbumin; and c ovotransferrin. All experiments were conducted in a 50 mM sodium phosphate buffer, 0.05% NaN₃, pH 7.4 With the addition of 100 mM NaCl and 1 Mm EDTA for α-lactalbumin at 37°C. The w/w ratio of protein/P. undulata extract is indicated. Note that all the experiments were done in three times. The error bars were very low and not plotted in the graph

Fig. 2

The maximum intrinsic fluorescence of target proteins (1 mg/mL) and P. undulata extract at different concentration. All experiments were incubated in a 50 mM sodium phosphate buffer, 0.05% NaN3 and pH 7.4 at 37°C for insulin in 1 h (a), for α-lactalbumin and ovotransferrin in 3 h (b, c)

Fig. 3

Average maximum ANS fluorescence bound of target protein (1 mg/mL) and P. undulata extract at different concentration. All experiments were conducted in a 50 mM sodium phosphate buffer, 0.05% NaN3 and pH 7.4 at 37°C for insulin (a), for α-lactalbumin (b), and ovotransferrin in (c)

Fig. 4

Near-UV CD spectra (a) and far-UV CD spectra (b) of insulin: unstressed (solid line), stressed (dashed line), stressed in the presence of P. undulata extract (dotted line)

Fig. 5

Near-UV CD spectra (a) and far-UV CD spectra (b) of α-lactalbumin: unstressed (solid line), stressed (dashed line), stressed in the presence of P. undulata extract (dotted line)

Fig. 6

Near-UV CD spectra (a) and far-UV CD spectra (b) of ovotransferrin: unstressed (solid line), stressed (dashed line), stressed in the presence of P. undulata extract (dotted line)

Scheme 1

Proposed mechanism of chaperone action of P. undulata extract in preventing protein aggregation