The recent rise of multidrug resistant microbial strains requires development of new and novel therapeutic alternatives. In this study, we present a novel antibacterial system that comprises of modified naturally abundant antimicrobial peptides in conjugation with silver nanoparticles. Further, we propose a simple route to incorporate a cysteine residue either at the N- or C-terminal of the parent peptide. Tagging a cysteine residue at the terminals not only enhances the binding propensity of the resultant peptide with the silver nanoparticle, but also increases its antimicrobial property against several pathogenic bacterial strains including K. pneumoniae. The minimum inhibitory concentration (MIC) values of the cysteine tagged nanoconjugates were obtained in the range of 5–15 μM compared to 50 μM for peptides devoid of the cysteines. The origin and mechanism of such improved activity of the conjugates were investigated using NMR spectroscopy and molecular dynamics (MD) simulations. The application of ¹³C-isotope labelled media to track the metabolic lifecycle of E. coli cells provided further insights into the system. MD simulations showed that pore formation in membrane bilayer is mediated through a hydrophobic collapse mechanism. The design strategy described herein opens up new-avenues for using biocompatible nanomedicines as a potential alternative to conventional antibiotics.

A non-toxic, nine residue peptide, NIVNVSLVK is shown to interfere with insulin fibrillation by various biophysical methods. Insulin undergoes conformational changes under certain stress conditions leading to amyloid fibrils. Fibrillation of insulin poses a problem in its long-term storage, reducing its efficacy in treating type II diabetes. The dissociation of insulin oligomer to monomer is the key step for the onset of fibrillation. The time course of insulin fibrillation at 62°C using Thioflavin T fluorescence shows an increase in the lag time from 120 min without peptide to 236 min with peptide. Transmission electron micrographs show branched insulin fibrils in its absence and less inter-fibril association in its presence. Upon incubation at 62°C and pH 2.6, insulin lost some α-helical structure as seen by Fourier transformed infra-red spectroscopy (FT-IR), but if the peptide is added, secondary structure is almost fully maintained for 3 h, though lost partially at 4 h. FT-IR spectroscopy also shows that insulin forms the cross beta structure indicative of fibrils beyond 2 h, but in the presence of the peptide, α-helix retention is seen till 4 h. Both size exclusion chromatography and dynamic light scattering show that insulin primarily exists as trimer, whose conversion to a monomer is resisted by the peptide. Saturation transfer difference nuclear magnetic resonance confirms that the hydrophobic residues in the peptide are in close contact with an insulin hydrophobic groove. Molecular dynamics simulations in conjunction with principal component analyses reveal how the peptide interrupts insulin fibrillation. In vitro hemolytic activity of the peptide showed insignificant cytotoxicity against HT1080 cells. The insulin aggregation is probed due to the inter play of two key residues, Phe^B24 and Tyr^B26 monitored from molecular dynamics simulations studies. Further new peptide based leads may be developed from this nine residue peptide.

This perspective article highlights the challenges in the theoretical description of photoreceptor proteins using multiscale modeling, as discussed at the CECAM workshop in Tel Aviv, Israel. The participants have identified grand challenges and discussed the development of new tools to address them. Recent progress in understanding representative proteins such as green fluorescent protein, photoactive yellow protein, phytochrome, and rhodopsin is presented, along with methodological developments.