Assessment of structural integrity of lysozyme in the presence of newly formed uni/multivesicular metallosomes

Abstract

Liposomes are promising modality for nano-medical applications. Thus, we are exploring an alternative for liposome like assembled structures prepared from metallosurfactants, commonly known as metallosomes. In this work, we have prepared Fe, Co, Ni and Cu based metallosomes using four different double chained metallosurfactants. The unilamellar structure of Fe and Co-metallosomes and multivesicular nature of Ni and Cu-metallosomes were investigated by transmission electron microscopy and small angle X-ray scattering analysis. This study further utilized Dynamic light scattering and Field emission scanning electron microscopy to confirm the morphology of synthesized metallosomes. The stability of metallosomes upto 5 days was checked by Dynamic light scattering. The metallosomes exhibited high encapsulation efficiency towards fluorescein dye which was clearly visible through confocal microscopy images. Further, with a view to explore biological applications, functional and structural integrity of lysozyme (Lyz) in the presence of synthesized metallosomes has been evaluated . Gel chromatography was performed to remove the free Lyz from Lyz-metallosomes complex. Metallosomes provides ground state complexation with Lyz as evident from absorbance spectroscopy and all the four metallosomes showed similar effects on the tertiary structure of protein. The fluorescence measurement indicated that the interactions are mainly hydrophobic in nature and ruled out the possibility of strong electrostatic interactions. The same was authenticated by the zeta potential measurements, where both the entities were of same (positive) charge. Interestingly, in the presence of metallosomes, secondary and primary structure of Lyz was damaged as evaluated from CD and gel electrophoresis, respectively. Enzyme activity of Lyz was also decreased in the presence of metallosomes. However, with the addition of Triton x-100, activity was increased due to destruction of metallosomes. Mainly, it is the role of hydrophobic interactions between the hydrophobic domains of metallosomes and Lyz that altered the structural integrity of protein. Since electrostatic interactions were weak in this system, therefore, the difference in the property due to variation of metal ion was less prominent.