Zn²⁺ and Cu²⁺ induced nanosheets and nanotubes in six different lectins by TEM

Abstract

Self assembly of biomolecules is important not only in unravelling the fundamental aspects of biology but also in exhibiting their supramolecular structures wherein the self assembly acts as a basic principle. Therefore, proteins having different side chains and structures with varying binding affinities towards metal ions can certainly be manifested in generating myriad supramolecular structures. In order to demonstrate this, we have chosen several β-sheet lectins, such as, Horse gram lectin (DBL), Pisum sativum agglutinin (PSA), Wheat germ agglutinin (WGA), Allium sativum agglutinin also known as garlic lectin (ASA) and Concanavalin A (Con A) lectin, in conjunction with Zn²⁺ and Cu²⁺ as biologically important ions and showed that these form nanostructures, such as, open-, rolled- and stacked sheets, and tubes. The Zn²⁺ induces mainly the sheets in the lectins studied so far though some of these are thin and others are thick, while some are folded and others are not. However, Cu²⁺ induces mainly tubes in ASA and DBL, predominantly sheets in Con A and a mixture of tubes and sheets in PSA and WGA as shown by TEM and supported by SEM. The tubes formed were thick as well as thin, solid as well as hollow in nature, straight, cylindrical as well as twisted and ribbon shaped. Plasmid PBR322 treated nanostructures formed from PSA in the presence of Cu²⁺ showed the presence of the plasmid in the corresponding tubes and sheets. These nanostructures are unprecedented and could lead to major advances in biomaterials science by providing potential applications.