Modeling and Designing Particle-Regulated Amyloid-like Assembly of Synthetic Polypeptides in Aqueous Solution

Abstract

In cells, actin and tubulin polymerization is regulated by nucleation factors, which promote the nucleation and subsequent growth of protein filaments in a controlled manner. Mimicking this natural mechanism to control the supramolecular polymerization of macromolecular monomers by artificially created nucleation factors remains a largely unmet challenge. Biological nucleation factors act as molecular scaffolds to boost the local concentrations of protein monomers and facilitate the required conformational changes to accelerate the nucleation and subsequent polymerization. An accelerated assembly of synthetic poly­(l-glutamic acid) into amyloid fibrils catalyzed by cationic silica nanoparticle clusters (NPCs) as artificial nucleation factors is demonstrated here and modeled as supramolecular polymerization with a surface-induced heterogeneous nucleation pathway. Kinetic studies of fibril growth coupled with mechanistic analysis demonstrate that the artificial nucleators predictably accelerate the supramolecular polymerization process by orders of magnitude (e.g., shortening the assembly time by more than 10 times) when compared to the uncatalyzed reaction, under otherwise identical conditions. Amyloid-like fibrillation was supported by a variety of standard characterization methods. Nucleation followed a Michaelis–Menten-like scheme for the cationic silica NPCs, while the corresponding anionic or neutral nanoparticles had no effect on fibrillation. This approach shows the effectiveness of charge–charge interactions and surface functionalities in facilitating the conformational change of macromolecular monomers and controlling the rates of nucleation for fibril growth. Molecular design approaches like these inspire the development of novel materials via biomimetic supramolecular polymerizations.

Tailoring Synthetic Polypeptide Design for Directed Fibril Superstructure Formation and Enhanced Hydrogel Properties

“…Unlike PGlu and most homopolypeptides, PLys can transform into hydrogels, consisting of elongated nanofibrils, when the side-chain charges neutralize under alkaline conditions (Figure S1). This transformation is notably rapid and devoid of the typical nucleation lag phases often seen in amyloid-like supramolecular assemblies. , Given Ser’s propensity for β-sheet structures − and its increased hydrophilicity compared to Glu in acidic environments where self-assembly occurs, it is anticipated to act as a catalyst in the formation of widespread, elongated fibrils. At sufficiently high concentrations, these copolypeptide fibrils are likely to intertwine swiftly to form a sample-spanning network, overcoming the stacking challenges of PGlu fibrils and offering a cohesive and stable hydrogel structure, circumventing precipitation constraints.…”

“…Fourier-transform infrared spectra (FTIR) and wide-angle X-ray diffraction (WAXD) of the fibrils revealed that they were primarily composed of β-sheet structures (Figure S16 and S17). The kinetics of fibrillation were examined using thioflavin T (ThT) , in a 15 mM acetate buffer (pH 4), monitoring the enhanced fluorescence emission upon ThT’s binding to β-sheet structures. TEM analysis confirmed that the fibril morphologies remained consistent in the presence of an acetate buffer (Figure S23).…”

“…This constraint restricts their broader application as viscoelastic biomaterials. For example, under acidic conditions, poly­( L -glutamic acid) (PGlu) forms amyloid-like fibrils that bundle into twisted ribbons. − This transformation is driven by the thermodynamic tendency for aggregated fibrils to adopt pairwise orientation. Instead of progressing to gel states, these fibrils often crystallize into spherulite microparticles and precipitate.…”

Recent advances in the solution self‐assembly of polypeptides

“…[10][11][12] The past two decades have witnessed significant advancements in polypeptide solution self-assembly, which have been summarized by several groups so far. [13][14][15][16] Recently, some remarkable advances have been achieved in the solution self-assembly of polypeptides.…”

“…A variety of polypeptide self‐assembly systems, including homopolymers, block and graft copolymers, and multi‐component systems, have been studied 10–12 . The past two decades have witnessed significant advancements in polypeptide solution self‐assembly, which have been summarized by several groups so far 13–16 …”