Investigation the protective ability of Pulicaria. undulata aqueous extract on aggregation of κ -casein

Protein aggregation is phenomenon wherein protein loses its native structure and aggregates due to the adaption of non-native conformation. Amyloid aggregation formed by the accumulation of various proteins causes many diseases in humans and other organisms. Antioxidants can prevent proteins aggregation. Pulicaria undulata  extract along with phenolic compounds can increase protein stability and prevent the aggregation of proteins. The aim of this study is to investigate the aggregation of reduced κ-casein in the presence and absence of P.undulata extract. Interaction between the extract and the κ-casein was investigated by Thioflavin T fluorescence, intrinsic fluorescence intensity, 1-Anilino-8-naphthalene sulfonic acid( ANS) binding assay and circular dichroism (CD) spectroscopy. The result of ThT binding assay indicated that the increase fluorescence intensity of 1,4- dithiothreithol(DTT)-reduced κ-casein is a result of amyloid fibril formation increased in the presence of different concentrations of P.undulata extract in the lag phase.  This indicates that P.undulata extract  reduces amyloid formation. And fluorescence test of reduced κ-casein indicates a high fluorescence intensity in the absence of P.undulata extract , and the fluorescence decreases when smallest amount of P.undulata extract was used. Using a fluorescence study of far-CD spectrum of κ-casein in the presence and absence of P.undulata extract revealed that the extract prevents changes in secondary structure in the protein. P.undulata extract interacts with the hydrophobic region of κ-casein and prevents hydrophobic-hydrophobic protein interaction and therefore protein aggregation.