Self-Blinking Thioflavin T for Super-resolution Imaging.

Thioflavin T (ThT) is a typical dye used to visualize the aggregation and formation of fibrillar structures, e.g., amyloid fibrils and peptide nanofibrils. ThT has been considered to produce stable fluorescence when interacting with aggregated proteins. For single-molecule localization microscopy (SMLM)-based optical super-resolution imaging, a photoswitching/blinking fluorescence property is required. Here we demonstrate that, in contrast to previous reports, ThT exhibits intrinsic stochastic blinking properties, without the need for blinking imaging buffer, in stable binding conditions. The blinking properties (photon number, blinking time, and on-off duty cycle) of ThT at the single-molecule level (for ultralow concentrations) were investigated under different conditions. As a proof of concept, we performed SMLM imaging of ThT-labeled α-synuclein fibrils measured in air and PBS buffer.

Liquid-Liquid Phase Separation of the Intrinsically Disordered Domain of the Fused in Sarcoma Protein Results in Substantial Slowing of Hydration Dynamics.

Formation of liquid condensates plays a critical role in biology via localization of different components or via altered hydrodynamic transport, yet the hydrogen-bonding environment within condensates, pivotal for solvation, has remained elusive. We explore the hydrogen-bond dynamics within condensates formed by the low-complexity domain of the fused in sarcoma protein. Probing the hydrogen-bond dynamics sensed by condensate proteins using two-dimensional infrared spectroscopy of the protein amide I vibrations, we find that frequency-frequency correlations of the amide I vibration decay on a picosecond time scale. Interestingly, these dynamics are markedly slower for proteins in the condensate than in a homogeneous protein solution, indicative of different hydration dynamics. All-atom molecular dynamics simulations confirm that lifetimes of hydrogen-bonds between water and the protein are longer in the condensates than in the protein in solution. Altered hydrogen-bonding dynamics may contribute to unique solvation and reaction dynamics in such condensates.

Effect of ambient temperature on respiratory tract cells exposed to SARS-CoV-2 viral mimicking nanospheres-An experimental study.

The novel coronavirus caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has reached more than 160 countries and has been declared a pandemic. SARS-CoV-2 infects host cells by binding to the angiotensin-converting enzyme 2 (ACE-2) surface receptor via the spike (S) receptor-binding protein (RBD) on the virus envelope. Global data on a similar infectious disease spread by SARS-CoV-1 in 2002 indicated improved stability of the virus at lower temperatures facilitating its high transmission in the community during colder months (December-February). Seasonal viral transmissions are strongly modulated by temperatures, which can impact viral trafficking into host cells; however, an experimental study of temperature-dependent activity of SARS-CoV-2 is still lacking. We mimicked SARS-CoV-2 with polymer beads coated with the SARS-CoV-2 S protein to study the effect of seasonal temperatures on the binding of virus-mimicking nanospheres to lung epithelia. The presence of the S protein RBD on nanosphere surfaces led to binding by Calu-3 airway epithelial cells via the ACE-2 receptor. Calu-3 and control fibroblast cells with S-RBD-coated nanospheres were incubated at 33 and 37 °C to mimic temperature fluctuations in the host respiratory tract, and we found no temperature dependence in contrast to nonspecific binding of bovine serum ablumin-coated nanospheres. Moreover, the ambient temperature changes from 4 to 40 °C had no effect on S-RBD-ACE-2 ligand-receptor binding and minimal effect on the S-RBD protein structure (up to 40 °C), though protein denaturing occurred at 51 °C. Our results suggest that ambient temperatures from 4 to 40 °C have little effect on the SARS-CoV-2-ACE-2 interaction in agreement with the infection data currently reported.

Type I Collagen from Jellyfish Catostylus mosaicus for Biomaterial Applications.

Collagen is the predominant protein in animal connective tissues and is widely used in tissue regeneration and other industrial applications. Marine organisms have gained interest as alternative, nonmammalian collagen sources for biomaterial applications because of potential medical and economic advantages. In this work, we present physicochemical and biofunctionality studies of acid solubilized collagen (ASC) from jellyfish Catostylus mosaicus (JASC), harvested from the Persian Gulf, compared with ASC from rat tail tendon (RASC), the industry-standard collagen used for biomedical research. From the protein subunit (alpha chain) pattern of JASC, we identified it as a type I collagen, and extensive molecular spectroscopic analyses showed similar triple helical molecular signatures for JASC and RASC. Atomic force microscopy of fibrillized JASC showed clear fibril reassembly upon pH neutralization though with different temperature and concentration dependence compared with RASC. Molecular (natively folded, nonfibrillized) JASC was shown to functionalize rigid substrates and promote MC3T3 preosteoblast cell attachment and proliferation better than RASC over 6 days. On blended collagen-agarose scaffolds, both RASC and JASC fibrils supported cell attachment and proliferation, and scaffolds with RASC fibrils showed more cell growth after 6 days compared with those scaffolds with JASC fibrils. These results demonstrate the potential for this new type I collagen as a possible alternative to mammalian type I collagen for biomaterial applications.

Measuring Intracellular Secondary Structure of a Cell-Penetrating Peptide in Situ.

Cell-penetrating peptides (CPPs) are short peptide sequences that can translocate across cellular plasma membranes and are thus potential delivery vectors for diagnostic and therapeutic applications. Many CPPs exhibit some sort of structural polymorphism, where the secondary structure of the peptide is altered strongly by its local environment, which is believed to facilitate membrane translocation and uptake. However, much less is known about the fate and structure of CPPs within cells largely due to measurement difficulty. Here we employ isotopic labeling combined with hyperspectral, quantitative coherent Raman microscopy to localize a model CPP-penetratin-and determine its secondary structure in different cellular compartments. Our results show that penetratin is mostly α-helical in the cytosol and acquires a more ß-sheet and random coil character in the nucleus. The increased helicity in the cytosol is similar to that seen in previous studies with model lipid membranes, suggesting that the peptide is associated with membranes in, e.g., endosomes (or lysosomes) in the cytosol. The ability to both localize and determine the secondary structure of a CPP within cells is critical for clarifying the mechanism of peptide-mediated translocation and delivery of cargo molecules to specific cellular destinations.

Bioinspired phosphorylcholine containing polymer films with silver nanoparticles combining antifouling and antibacterial properties.

The antibacterial (bioactive) and antifouling (biopassive) properties of stable, uniform, high surface coverage films of poly(hydroxyethyl methacrylate-co-2-methacryloyloxyethyl phosphorylcholine) (p(HEMA-co-MPC)) with embedded, non-leaching silver nanoparticles (AgNPs) are reported. Based on the experimental findings, a mechanism of action of AgNPs in antibacterial activity in combination with antifouling characteristics is discussed. Long-term antifouling studies of E. coli determine little to no adhesion on p(HEMA-co-MPC)/Ag films at 2.5 × 106 CFU mL-1 for 7 d, measured using live/dead staining assays. Agar diffusion tests indicate that there is no leaching of Ag from the films and SEM and EDX analyses of the films before and after incubation with E. coli show no attachment of E. coli and no visible change in film morphology or AgNP dispersal. Antibacterial studies are investigated using E. coli K-12 as a model bacterial strain and are tested in static (CFUs) and dynamic contact assays. Antibacterial efficacy of the films containing extremely low AgNP concentration (3.8 ng cm-2) is shown with growth suppression of E. coli in culture medium for 4 h at 1.35 × 105 CFU mL-1 and killing greater than 99% of E. coli in only 1 h of exposure to concentrations up to 1 × 105 CFU mL-1. These hybrid films may propose an exciting direction to long-term antibacterial and antifouling films in clinical applications.

Cationized albumin-biocoatings for the immobilization of lipid vesicles.

Tethered lipid membranes or immobilized lipid vesicles are frequently used as biomimetic systems. In this article, the authors presented a suitable method for efficient immobilization of lipid vesicles onto a broad range of surfaces, enabling analysis by quantitative methods even under rigid, mechanical conditions-bare surfaces such as hydrophilic glass surfaces as well as hydrophobic polymer slides or metal surfaces such as gold. The immobilization of vesicles was based on the electrostatic interaction of zwitterionic or negatively charged lipid vesicles with two types of cationic chemically modified bovine serum albumin (cBSA) blood plasma proteins (cBSA-113 and cBSA-147). Quantitative analysis of protein adsorption was performed as the cBSA coatings were characterized by atomic force microscopy, surface zeta potential measurement, fluorescence microscopy, and surface plasmon spectroscopy, revealing a maximal surface coverage 270-280 ng/cm(2) for 0.02 mg/ml cBSA on gold. Small unilamellar vesicles as well as giant unilamellar vesicles (GUVs) were readily immobilized (∼15 min) on cBSA coated surfaces. GUVs with 5-10 mol% negatively charged 1,2,-dipalmitoyl-sn-glycero-3-phosphoglycerol remained stable in liquid for at least 5 weeks.