(673a) Computational Studies on Cyclo-Dihistidine Self-Assembly into Nanostructures with Enhanced Fluorescence and Drug Encapsulation Properties

Self-assembled peptides, through extensive and directed hydrogen bonding and aromatic interactions, is increasingly gaining interest for the development of biocompatible and biodegradable functional biomaterials. A reductionist approach, aiming to identify the shortest self-assembling peptide motifs, allowed for the identification of extremely short peptides, such as diphenylalanine, which could form well-ordered amyloid-like assemblies comparable to supramolecular structures formed by much larger proteins. Analogously to diphenylalanine, cyclo-dihistidine (cyclo-HH) is a minimalistic self-assembling peptide, inspired by the green fluorescent protein mutant BFPms1, which forms a peptide material with high-fluorescence efficiency that can be applied as multifunctional nanomaterials with exceptional features for optoelectronic or biological applications. In two recently published studies, we used a combination of experimental and computational methods to investigate the self-assembly properties of cyclo-HH and exploit the self-assembled cyclo-HH nanostructures for biomedical applications^1,2.

We used molecular dynamics simulations (MD) and free energy calculations to investigate the initial nucleation stages of cyclo-HH self-assembly in the presence and absence of Zn(II). According to MD simulations cyclo-HH self-assembled both in the presence or absence of Zn(II). However, in the absence of Zn(II), cyclo-HH tended to form parallel β-bridge conformations, while in the presence of Zn(II), pairs of cyclo-HH tended to form anti-parallel β-bridge conformations, consistent with X-ray crystallography structures. Based on structural analysis and free energy calculations, in the initial stages of cyclo-HH self-assembly in the presence of Zn(II) the metal ions are initially attracted and pulled from the solvent to a more peptide‐rich, low dielectric environment, thus giving rise to an "environment‐switching" doping mechanism¹. We then investigated the self-assembly of cyclo-HH in the presence of Zn(II) and nitrate anions (NO₃^-) using additional simulations which depicted that cyclo-HH, Zn(II), and NO₃^- self-assemble in a "self-assembly locking strategy" in which the fluorescent cyclo-HH−Zn(II) nucleus is first formed and then encased by the cyclo-HH−NO₃ scaffold². Additional simulations of cyclo-HH in the presence of Zn(II), NO₃^- and cancer drug Epirubicin, showed that Epirubicin and Zn(II) were self-encapsulated by cyclo-HH and NO₃in the aggregates². We employed the “self-encapsulation” strategy of cyclo-HH−Zn(NO₃)₂ for Epirubicin traceable intracellular drug delivery in experiments which showed that cyclo-HH−Zn(NO₃)₂ not only promoted the transport of Epirubicin into HeLa cells but also can act as a real-time optical monitor for the drug release process².

1. Tao K, Chen Y, Orr AA, Tian Z, MakamP, Gilead S, Si M, Rencus-Lazar S, Qu S, Zhang M, Tamamis P, GazitP. Enhanced Fluorescence for Bioassembly by Environment-Switching Doping of Metal Ions. Adv. Funct. Mater. 2020, 1909614.
2. Chen Y, Orr AA, Tao K, Wang Z, Ruggiero A, Shimon LJW, Schnaider L, Goodall A, Rencus-Lazar S, Gilead S, Slutsky I, Tamamis P, Tan Z, Gazit E. High-Efficiency Fluorescence through Bioinspired Supramolecular Self-Assembly. ACS Nano. 2020. doi: 10.1021/acsnano.9b10024.