Effect of Metal Ions on the Interaction of Condensed Tannins with Protein

A quantitative analysis of the precipitate effects of metal ions (Al³⁺, Fe²⁺, Cu²⁺, Zn²⁺) by bovine serum albumin (BSA) on two condensed tannins (CT) from sorghum and plum was presented in this study. The results showed that adding metal ions enhanced the precipitation of proteins by CT, depending on the type and concentration of the metal ions used in the reaction system. The presence of metal ions and precipitation results on the CT-protein complex showed that Al³⁺ and Fe²⁺ had a higher binding ability with CT and a weaker influence on the precipitation of the CT-protein complex than Cu²⁺ and Zn²⁺. However, when the initial reaction solution contained excessive amounts of BSA, the extra addition of metal ions had no significant effect on the amount of BSA precipitation. Reversely, adding Cu²⁺ or Zn²⁺ into the reaction solution increased the amount of precipitated BSA when the amount of CT was excessive. In addition, the amounts of CT from plum, rather than sorghum, generated more protein precipitate in the presence of Cu²⁺ or Zn²⁺, which may be due to the different binding modes between the metal ion and the CT-BSA complex. This study also proposed a model of the interaction between the metal ion and the CT-protein precipitate.

Studies on binding of single-stranded DNA with reduced graphene oxide-silver nanocomposites

The binding reaction of reduced graphene oxide-silver nanocomposites (rGO-AgNCs) with calf thymus single-stranded DNA (ssDNA) was studied by ultraviolet-visible absorption, fluorescence spectroscopy and circular dichroism (CD), using berberine hemisulphate (BR) dye as a fluorescence probe. The absorbance of ssDNA increases, but the fluorescence intensity is quenched with the addition of rGO-AgNCs. The binding of rGO-AgNCs with ssDNA was able to increase the quenching effects of BR and ssDNA, and induce the changes in CD spectra. All of the evidence indicated that there was a relatively strong interaction between ssDNA and rGO-AgNCs. The data obtained from fluorescence experiments revealed that the quenching process of ssDNA caused by rGO-AgNCs is primarily due to complex formation, i.e. static quenching. The increasing trend of the binding equilibrium constant (Ka) with rising temperature indicated that the binding process was an endothermic reaction. The calculated thermodynamic parameters showed that the binding process was thermodynamically spontaneous, and hydrophobic association played predominant roles in the binding of ssDNA to the surface of rGO-AgNCs.

Quantitative Measurement of Spatial Effects of DNA Origami on Molecular Binding Reactions Detected using Atomic Force Microscopy

DNA origami is a ubiquitous nanostructure that can be used as a universal scaffold for constructing molecular motors, nanosensors, nanodrugs, and optical devices. Understanding the inherent heterogeneity of DNA origami structures is crucial for optimizing the design of high-efficiency nanosized-devices. Here, we investigated the spatial effects of the DNA origami on binding reactions using atomic force microscopy. Protein complexes formed more efficiently at the vertex and rim than on the surface of the DNA origami; surprisingly, the maximum difference in biotin-streptavidin binding efficiency was over 80%, and the change in the binding rate was approximately 40-fold, suggesting the presence of distinct microenvironments at different locations of the DNA origami. Our findings are not only useful for the potential applications of the DNA origami, but also for clarifying differences in nanomaterials caused by nonuniform distribution or defects.