Reconstitution and Functional Analysis of a Full-Length Hepatitis C Virus NS5B Polymerase on a Supported Lipid Bilayer

Arginine replacement of histidine on temporin-GHa enhances the antimicrobial and antibiofilm efficacy against Staphylococcus aureus

Antimicrobial peptides (AMPs) show broad-spectrum microbicidal activity against bacteria, fungi, and viruses, and have been considered as one of the most promising candidates to overcome bacterial antimicrobial resistance. Structural modification of AMPs is an effective strategy to develop high-efficiency and low-toxicity antibacterial agents. A series of peptides GHaR6R, GHaR7R, GHaR8R, and GHaR9W with arginine replacement of histidine (His) derived from temporin-GHa of Hylarana guentheri were designed and synthesized. These derived peptides exhibit antibacterial activity against Staphylococcus aureus, and GHaR8R exerts bactericidal effect within 15 min at 4 × MIC (25 µm). The derived peptides caused rapid depolarization of bacteria, and the cell membrane damage was monitored using quartz crystal microbalance with dissipation assay, which suggests that they target cell membranes to exert antibacterial effects. The derived peptides can effectively eradicate mature biofilms of S. aureus. Taken together, the derived peptides are promising antibacterial agent candidates against S. aureus.

DNA Framework-Mediated Geometric Renormalization of Gold Nanoparticles on a Two-Dimensional Fluidic Membrane Interface

The precise arrangement of single entity is a crucial objective of nanoscience and holds great promise in various fields such as biology and material science. In this work, we develop a "DNA framework-mediated geometric renormalization" (DFMGR) strategy to reassemble gold nanoparticles into specific geometric shapes on a 2-dimensional (2D) fluidic membrane interface. Cholesterol-modified AuNPs are randomly anchored on the supported lipid bilayer (SLB) via the cholesterol-lipid interaction. We demonstrate that AuNPs are laterally mobile on SLB and could be further rearranged into a specific geometric shape by DNA framework containing algebraically topological DNA arms. Using scanning electron microscope (SEM) imaging approach, simple geometric shapes, such as points assembled by monomers, line segments assembled by dimers, triangles assembled by trimers are visually presented. Interestingly, we found that the statistic angle (58.77°) and side length (12.21 nm) of triangles obtained from SEM images were both agreed well with the theoretical angle of 60° and side length of 12.58 nm. And the relative error of the angle calculated was as low as 0.33 %. These results indicated that the DFMGR strategy showed precise regulation ability for the AuNPs renormalization. We believe that DNA framework-mediated geometric renormalization strategy would be a powerful means for regulating ligand-receptor interactions in biosystems and for nanoparticle assembling in material science.

NMR reveals the intrinsically disordered domain 2 of NS5A protein as an allosteric regulator of the hepatitis C virus RNA polymerase NS5B

Non-structural protein 5B (NS5B) is the RNA-dependent RNA polymerase that catalyzes replication of the hepatitis C virus (HCV) RNA genome and therefore is central for its life cycle. NS5B interacts with the intrinsically disordered domain 2 of NS5A (NS5A-D2), another essential multifunctional HCV protein that is required for RNA replication. As a result, these two proteins represent important targets for anti-HCV chemotherapies. Despite this importance and the existence of NS5B crystal structures, our understanding of the conformational and dynamic behavior of NS5B in solution and its relationship with NS5A-D2 remains incomplete. To address these points, we report the first detailed NMR spectroscopic study of HCV NS5B lacking its membrane anchor (NS5B_Δ21). Analysis of constructs with selective isotope labeling of the δ1 methyl groups of isoleucine side chains demonstrates that, in solution, NS5B_Δ21 is highly dynamic but predominantly adopts a closed conformation. The addition of NS5A-D2 leads to spectral changes indicative of binding to both allosteric thumb sites I and II of NS5B_Δ21 and induces long-range perturbations that affect the RNA-binding properties of the polymerase. We compared these modifications with the short- and long-range effects triggered in NS5B_Δ21 upon binding of filibuvir, an allosteric inhibitor. We demonstrate that filibuvir-bound NS5B_Δ21 is strongly impaired in the binding of both NS5A-D2 and RNA. NS5A-D2 induces conformational and functional perturbations in NS5B similar to those triggered by filibuvir. Thus, our work highlights NS5A-D2 as an allosteric regulator of the HCV polymerase and provides new insight into the dynamics of NS5B in solution.

Solid surface vs. liquid surface: nanoarchitectonics, molecular machines, and DNA origami

Comparisons of science and technology between these solid and liquid surfaces would be a good navigation for current-to-future developments.

Desmosterol Increases Lipid Bilayer Fluidity during Hepatitis C Virus Infection

Hepatitis C virus (HCV) uniquely affects desmosterol homeostasis by increasing its intracellular abundance and affecting its localization. These effects are important for productive viral replication because the inhibition of desmosterol synthesis has an antiviral effect that can be rescued by the addition of exogenous desmosterol. Here, we use subgenomic replicons to show that desmosterol has a major effect on the replication of HCV JFH1 RNA. Fluorescence recovery after photobleaching (FRAP) experiments performed with synthetic supported lipid bilayers demonstrate that the substitution of desmosterol for cholesterol significantly increases the lipid bilayer fluidity, especially in the presence of saturated phospholipids and ceramides. We demonstrate using LC-MS that desmosterol is abundant in the membranes upon which genome replication takes place and that supported lipid bilayers derived from these specialized membranes also exhibit significantly higher fluidity compared to that of negative control membranes isolated from cells lacking HCV. Together, these data suggest a model in which the fluidity-promoting effects of desmosterol on lipid bilayers play a crucial role in the extensive membrane remodeling that takes place in the endoplasmic reticulum during HCV infection. We anticipate that the supported lipid bilayer system described can provide a useful model system in which to interrogate the effects of lipid structure and composition on the biophysical properties of lipid membranes as well as their function in viral processes such as genome replication.