Lysozyme encapsulated gold nanocluster for studying protein denaturation

Abstract

Protein denaturation is a change in a protein's structure from its native folded state to a non-native misfolded state. Protein denaturation is the cause of many diseases. Current methods used for protein denaturation studies have provided useful information regarding protein structures, but have limitations, such as their inability to detect early aggregation of protein; hence, a new method for detecting early aggregation is needed. Lysozyme-encapsulated gold nanoclusters (Lyz-AuNCs) have interesting fluorescence properties that can be used in a variety of fluorescence measurement techniques and maybe a promising tool for studying protein denaturation. So far, studies of the fluorescence characteristics of Lyz-AuNCs under protein denaturation conditions, and their correlation to protein unfolding, have been limited. The goal of this research was, therefore, to discover the influence of environmental factors and protein denaturation on the fluorescence properties of Lyz-AuNCs and further explore the potential of Lyz-AuNCs to inhibit human beta-amyloid (1-40) Aβ40 aggregation.;In our study, changes in pH were observed to alter the fluorescence properties of Lyz-AuNCs. At an excitation wavelength 470 nm, the fluorescence intensity of AuNCs increased and redshifted when the pH is increased from pH 7 to 12. This increase correlated to a decrease in its fluorescence lifetime, suggesting a possible mechanism of the enhanced radiative process. Moreover, hen egg-white lysozyme (HEWL) was added to Lyz-AuNCs solutions to study the effect of HEWL concentrations on their fluorescence properties. Especially, the fluorescence lifetime was found to be sensitive to the concentration of HEWL at pH 3, possibly due to the aggregation that changed the local environment. Furthermore, unfolding of Lyz-AuNCs was induced by urea, sodium dodecyl sulphate and elevated temperature. It was found that the fluorescence intensity of Lyz-AuNCs decreased due to increased collisional quenching. Finally, the interaction between Aβ40 and Lyz-AuNCs was studied. The observed decrease in fluorescence intensity was believed to be due to static quenching. Significantly, Lyz-AuNCs was found to inhibit Aβ40 fibre formation. This result suggested Lyz-AuNCs as a promising candidate for Alzheimer's disease (AD) treatment as well as a probe to study Aβ40 accumulation in AD pathology.Protein denaturation is a change in a protein's structure from its native folded state to a non-native misfolded state. Protein denaturation is the cause of many diseases. Current methods used for protein denaturation studies have provided useful information regarding protein structures, but have limitations, such as their inability to detect early aggregation of protein; hence, a new method for detecting early aggregation is needed. Lysozyme-encapsulated gold nanoclusters (Lyz-AuNCs) have interesting fluorescence properties that can be used in a variety of fluorescence measurement techniques and maybe a promising tool for studying protein denaturation. So far, studies of the fluorescence characteristics of Lyz-AuNCs under protein denaturation conditions, and their correlation to protein unfolding, have been limited. The goal of this research was, therefore, to discover the influence of environmental factors and protein denaturation on the fluorescence properties of Lyz-AuNCs and further explore the potential of Lyz-AuNCs to inhibit human beta-amyloid (1-40) Aβ40 aggregation.;In our study, changes in pH were observed to alter the fluorescence properties of Lyz-AuNCs. At an excitation wavelength 470 nm, the fluorescence intensity of AuNCs increased and redshifted when the pH is increased from pH 7 to 12. This increase correlated to a decrease in its fluorescence lifetime, suggesting a possible mechanism of the enhanced radiative process. Moreover, hen egg-white lysozyme (HEWL) was added to Lyz-AuNCs solutions to study the effect of HEWL concentrations on their fluorescence properties. Especially, the fluorescence lifetime was found to be sensitive to the concentration of HEWL at pH 3, possibly due to the aggregation that changed the local environment. Furthermore, unfolding of Lyz-AuNCs was induced by urea, sodium dodecyl sulphate and elevated temperature. It was found that the fluorescence intensity of Lyz-AuNCs decreased due to increased collisional quenching. Finally, the interaction between Aβ40 and Lyz-AuNCs was studied. The observed decrease in fluorescence intensity was believed to be due to static quenching. Significantly, Lyz-AuNCs was found to inhibit Aβ40 fibre formation. This result suggested Lyz-AuNCs as a promising candidate for Alzheimer's disease (AD) treatment as well as a probe to study Aβ40 accumulation in AD pathology