Reversible and biocompatible AuNP-decorated [Zn2+]:[Insulin] condensed assembly for potential therapeutic applications.

The present study reports the construction of Gold Nanoparticle (AuNP)-decorated [Zn2+]:[Insulin] condensed assembly which was found to be reversible and biocompatible. At first, Citrate-Capped AuNPs were synthesized using the Turkevich method, and the colloidal solution was co-incubated with [Zn2+]:[Insulin] maintaining an equimolar stoichiometry, at physiological pH, 60 °C and 6 h. Accordingly, the effect of excess Zn2+ and surface sorption events were investigated. The surface chemistry of protein sorption on AuNPs involved interaction of surface citrate with the amyloidogenic residues of insulin Chain A (L13, E17, N18) and Chain B (V12, Y16, L17), and also C7:A, C7:B, C20:A. The surface sorption involved a number of driving forces which were predicted to be covalent, H-bonding and hydrophobic interactions. Upon the capture of a fraction of insulin molecules, the Zn2+ was found to form cross-links between the unbound monomers and insulin bound on AuNP, thus forming nucleating species with dendritic morphology. The dendritic species self-assembled into linear and branched organization, followed by the formation of densely packed AuNP-decorated [Zn2+]:[Insulin] condensed assembly. Subsequently, alteration of pH resulted in changes of local charges, thus destabilizing the intermolecular ionic interactions, and subsequently caused the reversal of the condensed assembly back to monomeric forms. Furthermore, the reversible AuNP-decorated [Zn2+]:[Insulin] condensate was found to be biocompatible, and promoted the growth of the adherent cell line, BHK-21 fibroblasts. The non-cytotoxic and reversible material thus formed might have enormous applications in bioelectronics, cell culture matrices, and drug-delivery systems.

Supramolecular organization of Cytochrome-C into quantum-dot decorated macromolecular network under pH and thermal stress.

The holo form of Cytochrome-C which is involved in the electron transfer chain of aerobic and anaerobic respiration remains structurally intact by its complex with heme. However, when a prolonged thermal and pH stress was applied, heme was found to abruptly dissociate from the holo protein, resulting in complete collapse of the three-dimensional functional structure. Interestingly, two distinct structures were formed as the consequence of the dissociation event: (i) A macromolecular amyloid-network formed by the collapsed protein fragments, generated by self-oxidation, and (ii) Fe-containing Quantum-Dots (FeQDs) with 2-3 nm diameter formed by heme reorganization. Further adding to intrigue, the FeQDs were re-adsorbed on the surface of the amyloid network leading to FeQD-decorated macromolecular amyloid matrix. The heme-interactant Met80, constituting the amyloidogenic region, initiates the amylogenic cascade, and gradual exposure of Trp59 synergistically emit intrinsic fluorescence alongside FeQDs. The development of the aforementioned events were probed through a multitude of biophysical, chemical and computational analyses like ThT/ANS/intrinsic fluorescence assays, CD-spectroscopy, FETEM/STEM/elemental mapping, Foldamyloid/Foldunfold/Isunstruct/H-protection/LIGplot analyses, etc. The FeQD-decorated amyloid-network was found to exhibit gel-like property, which supported the growth of BHK-21 fibroblast without cytotoxicity. Further studies on FeQD-decorated Cytochrome C amyloid network might open possibilities to design advanced biomaterial for diverse biological applications.