The Effect of Polyethylene Glycol Induced Molecular Crowding on β-lactoglobulin Aggregation

In vitro protein aggregation is affected by many different factors such as the presence of crowder agents. As we know the intracellular environment is highly crowded and it contains high concentrations of macromolecules. Molecular crowding decreases the effective volume available for the proteins and affects protein–protein interactions like protein aggregation. Aggregation of proteins may lead to conformational changes and consequent conformational diseases. It is possible to mimic crowding condition in vitro by adding inert molecule such as polyethylene glycol (PEG). In this study, the effect of different concentrations of PEG was evaluated on β-lactoglobulin (BLG) aggregation at different pHs. It was also aimed to see if the environmental factor like pH could affect the protein aggregation. BLG aggregation was detected by UV-vis spectroscopy. The protein conformational changes were also examined by spectrofluorometer. SDS-PAGE method was applied to verify the disulfide bonds involvement in BLG aggregation. According to UV-vis spectroscopy data, BLG absorbance increased at higher concentrations of PEG. PEG induced aggregation was also influenced by physical parameter pH. Based on fluorescence results, PEG affected BLG compactness. SDS-PAGE showed that increasing of protein concentration induces more chemical aggregation. As a conclusion, crowding agent, PEG, induces protein aggregation and pH affects this process. This causes protein conformational destruction and may alter BLG function.