Dynamics of long-term protein aggregation on low-fouling surfaces

Advanced imaging techniques for studying protein phase separation in living cells and at single-molecule level

Protein-protein and protein-RNA interactions are essential for cell function and survival. These interactions facilitate the formation of ribonucleoprotein complexes and biomolecular condensates via phase separation. Such assembly is involved in transcription, splicing, translation and stress response. When dysregulated, proteins and RNA can undergo irreversible aggregation which can be cytotoxic and pathogenic. Despite technical advances in investigating biomolecular condensates, achieving the necessary spatiotemporal resolution to deduce the parameters that govern their assembly and behavior has been challenging. Many laboratories have applied advanced microscopy methods for imaging condensates. For example, single molecule imaging methods have enabled the detection of RNA-protein interaction, protein-protein interaction, protein conformational dynamics, and diffusional motion of molecules that report on the intrinsic molecular interactions underlying liquid-liquid phase separation. This review will outline advances in both microscopy and spectroscopy techniques which allow single molecule detection and imaging, and how these techniques can be used to probe unique aspects of biomolecular condensates.

Designing Non-Textured, All-Solid, Slippery Hydrophilic Surfaces

Slippery surfaces are sought after due to their wide range of applications in self-cleaning, drag reduction, fouling-resistance, enhanced condensation, biomedical implants etc. Recently, non-textured, all-solid, slippery surfaces have gained significant attention because of their advantages over super-repellent surfaces and lubricant-infused surfaces. Currently, almost all non-textured, all-solid, slippery surfaces are hydrophobic. In this work, we elucidate the systematic design of non-textured, all-solid, slippery hydrophilic (SLIC) surfaces by covalently grafting polyethylene glycol (PEG) brushes to smooth substrates. Furthermore, we postulate a plateau in slipperiness above a critical grafting density, which occurs when the tethered brush size is equal to the inter-tether distance. Our SLIC surfaces demonstrate exceptional performance in condensation and fouling-resistance compared to non-slippery hydrophilic surfaces and slippery hydrophobic surfaces. Based on these results, SLIC surfaces constitute an emerging class of surfaces with the potential to benefit multiple technological landscapes ranging from thermofluidics to biofluidics.

Comparative Study of the Solid-Liquid Interfacial Adsorption of Proteins in Their Native and Amyloid Forms

The adhesive properties of amyloid fibers are thought to play a crucial role in various negative and positive aggregation processes, the study of which might help in their understanding and control. Amyloids have been prepared from two proteins, lysozyme and β-lactoglobulin, as well as an Exendin-4 derivative miniprotein (E5). Thermal treatment was applied to form amyloids and their structure was verified by thioflavin T (ThT), 8-Anilino-1-naphthalenesulfonic acid (ANS) dye tests and electronic circular dichroism spectroscopy (ECD). Adsorption properties of the native and amyloid forms of the three proteins were investigated and compared using the mass-sensitive quartz crystal microbalance (QCM) technique. Due to the possible electrostatic and hydrophobic interactions, similar adsorbed amounts were found for the native or amyloid forms, while the structures of the adsorbed layers differed significantly. Native proteins formed smooth and dense adsorption layers. On the contrary, a viscoelastic, highly loose layer was formed in the presence of the amyloid forms, shown by increased motional resistance values determined by the QCM technique and also indicated by atomic force microscopy (AFM) and wettability measurements. The elongated structure and increased hydrophobicity of amyloids might contribute to this kind of aggregation.

Observation of two-step aggregation kinetics of Amyloid-βproteins from fractal analysis

Self-aggregation in proteins has long been studied and modeled due to its ubiquity and importance in many biological contexts. Several models propose a two step aggregation mechanism, consisting of linear growth of fibrils and secondary growth involving branch formation. Single molecule imaging techniques such as total internal reflection fluorescence (TIRF) microscopy can provide direct evidence of such mechanisms, however, analyzing such large data-sets is challenging. In this paper, we analyze for the first time, images of growing amyloid fibrils obtained from TIRF microscopy using the techniques of fractal geometry, which provides a natural framework to disentangle the two types of growth mechanisms at play. We find that after an initial linear growth phase, identified by a plateau in the average fractal dimension with time, the occurrence of branching events leads to a further increase in the fractal dimension, with a final saturation value ≈ 2. This provides direct evidence of the two-step nature of the aggregation kinetics of Amyloid-βproteins, with an initial linear elongation phase followed by branching at later times.

Adsorption properties of albumin and fibrinogen on hydrophilic/hydrophobic TiO2 surfaces: A molecular dynamics study

In serval experimental researches, UV-induced hydrophilicity enabled better hemocompatibility in the TiO₂ surface, which was considered to be caused by the removal of the carboxylic acid contamination from the surface. In this paper, we altered the surface wetting property by applying the formate contamination on the rutile (110) surface, and systematically investigated the adsorption properties of albumin and fibrinogen on hydrophilic/hydrophobic TiO₂ surface. Unique contacts were found between the charged residues and the hydrophilic surface, anchoring the protein on the surface. The small size and the heart shape of albumin make it easy to cross the stable water layers near the surface. Besides, albumin has a higher proportion of charged residues, so it can form more unique contacts on the hydrophilic surface. Therefore, the albumin tends to adsorb on the hydrophilic surface. For the hydrophobic surface, the water layers near the surface are weakened, which helps the fibrinogen diffusing to the surface and adjusting its orientation. Although the hydrophobic surface cannot form the unique contacts, the larger size of fibrinogen can provide more residues to form enough ordinary contacts after adjusting, and then achieves stable adsorption. Therefore, fibrinogen tends to adsorb on the hydrophobic surface.