Multistep molecular mechanism of amyloid-like aggregation of nucleic acid-binding domain of TDP-43

TDP-43 protein is associated with many neurodegenerative diseases and has been shown to adopt various oligomeric and fibrillar states. However, a detailed kinetic understanding of the structural transformation of the native form of the protein to the fibrillar state is missing. In this study, we delineate the temporal sequence of structural events during the amyloid-like assembly of the functional nucleic acid-binding domain of TDP-43. We kinetically mapped the aggregation process using multiple probes such as tryptophan and thioflavin T (ThT) fluorescence, circular dichroism (CD), and dynamic light scattering (DLS) targeting different structural events. Our data reveal that aggregation occurs in four distinct steps-very fast, fast, slow, and very slow. The "very fast" change results in partially unfolded forms that undergo conformational conversion, oligomerization and bind to ThT in the "fast step" to form higher order intermediates (HOI). The temporal sequence of the formation of ThT binding sites and conformational conversion depends upon the protein concentration. The HOI further undergoes structural rearrangement to form protofibrils in the "slow" step, which, consequently, assembles in the "very slow" step to form an amyloid-like assembly. The spectroscopic properties of the amyloid-like assembly across the protein concentration remain similar. Additionally, we observe no lag phase across protein concentration for all the probes studied, suggesting that the aggregation process follows a linear polymerization reaction. Overall, our study demonstrates that the amyloid-like assembly forms in multiple steps, which is also supported by the temperature dependence of the kinetics.

Amyloid-Like Protein Aggregates: A New Class of Bioinspired Materials Merging an Interfacial Anchor with Antifouling

Surfaces that resist nonspecific protein adsorption in a complex biological milieu are required for a variety of applications. However, few strategies can achieve a robust antifouling coating on a surface in an easy and reliable way, regardless of material type, morphology, and shape. Herein, the preparation of an antifouling coating by one-step aqueous supramolecular assembly of bovine serum albumin (BSA) is reported. Based on fast amyloid-like protein aggregation through the rapid reduction of the intramolecular disulfide bonds of BSA by tris(2-carboxyethyl)phosphine, a dense proteinaceous nanofilm with controllable thickness (≈130 nm) can be covered on virtually arbitrary material surfaces in tens of minutes by a simple dipping or spraying. The nanofilm shows strong stability and adhesion with the underlying substrate, exhibiting excellent resistance to the nonspecific adsorption of a broad-spectrum of contaminants including proteins, serum, cell lysate, cells, and microbes, etc. In vitro and in vivo experiments show that the nanofilm can prevent the adhesion of microorganisms and the formation of biofilm. Compared with native BSA, the proteinaceous nanofilm coating exposes a variety of functional groups on the surface, which have more-stable adhesion with the surface and can maintain the antifouling in harsh conditions including under ultrasound, surfactants, organic solvents, and enzymatic digestion.

Amyloid-Like Rapid Surface Modification for Antifouling and In-Depth Remineralization of Dentine Tubules to Treat Dental Hypersensitivity

Exposure of dentinal tubules (DTs) leads to the transmission of external stimuli within the DTs, causing dental hypersensitivity (DH). To treat DH, various desensitizers have been developed for occluding DTs. However, most desensitizers commercially available or in development are only able to seal the orifices, rather than the deep regions of the DTs, thus lacking long-term stability. Herein, it is shown that the fast amyloid-like aggregation of lysozyme (lyso) conjugated with poly(ethylene glycol) (PEG) (lyso-PEG) can afford a robust ultrathin nanofilm on the deep walls of DTs through a rapid one-step aqueous coating process (in 2 min). The resultant nanofilm provides a highly effective antifouling platform for resisting the attachment of oral bacteria such as Streptococcus mutans and induces remineralization in the DTs to seal both the orifices and depths of the DTs by forming hydroxyapatite (HAp) minerals in situ. Both in vitro and in vivo animal experiments prove that the nanofilm-coated DTs are occluded with a depth of over 60 ± 5 µ m, which is at least 6 times deeper than that reported in the literature. This approach thus demonstrates the concept that an amyloid-like proteinaceous nanofilm can offer an inexpensive, rapid, and efficient therapy for treating DH with long-term effect.

Sn-Triggered Two-Dimensional Fast Protein Assembly with Emergent Functions

The discovery of a general strategy for organizing functional proteins into stable nanostructures with the desired dimension, shape, and function is an important focus in developing protein-based self-assembled materials, but the scalable synthesis of such materials and transfer to other substrates remain great challenges. We herein tackle this issue by creating a two-dimensional metal-protein hybrid nanofilm that is flexible and cost-effective with reliable self-recovery, stability, and multifunctionality. As it differs from traditional metal ions, we discover the capability of Sn²⁺ to initiate fast amyloid-like protein assembly (occurring in seconds) by effectively reducing the disulfide bonds of native globular proteins. The Sn²⁺-initiated lysozyme aggregation at the air/water interface leads to droplet flattening, a result never before reported in a protein system, which finally affords a multifunctional 2D Sn-doped hybrid lysozyme nanofilm with an ultralarge area (e.g., 0.2 m²) within a few minutes. The hybrid film is distinctive in its ease of coating on versatile material surfaces with endurable chemical and mechanical stability, optical transparency, and diverse end uses in antimicrobial and photo-/electrocatalytic scaffolds. Our approach provides not only insights into the effect of tin ions on macroscopic self-assembly of proteins but also a controllable and scalable synthesis of a potential biomimic framework for biomedical and biocatalytic applications.