Surface Tension, Viscosity, and Refractive Index of Sodium Dodecyl Sulfate (SDS) in Aqueous Solution Containing Poly(ethylene glycol) (PEG), Poly(vinyl pyrrolidone) (PVP), and Their Blends

Taking into consideration the importance of the polymer–surfactant system, in present manuscript we discuss the intermolecular interactions present in solution containing sodium dodecyl sulfate (SDS) in six different solvent concentrations of polymer and their mixtures in their mass ratio [1 g of PEG (<i>m</i>₁), 0.8:0.2 PEG/PVP (<i>m</i>₂), 0.6:0.4 PEG/PVP (<i>m</i>₃), 0.4:0.6 PEG/PVP (<i>m</i>₄), 0.2:0.8 PEG/PVP (<i>m</i>₅), and 1 g of PVP (<i>m</i>₆) in 100 mL of distilled water] having a molal concentration corresponding to 1.66 mmol·kg^–1, 1.38 mmol·kg^–1, 1.10 mmol·kg^–1, 0.81 mmol·kg^–1, 0.53 mmol·kg^–1, and 0.25 mmol·kg^–1, respectively. It suffices to mention here that the concentration (molality) corresponds to the total polymer content in the solution. All of the measurements were carried out at three different temperatures, that is, 293.15, 303.15, and 313.15 K. The whole experiment was carried out with techniques like surface tension, viscosity, and refractive index measurements. Different parameters of relevance like surface excess (Γ_max), minimum area per molecule at air–water interface (<i>A</i>_min), relative viscosity (η_r), viscous relaxation time (τ), and limiting dielectric constant (ε_∞), and so forth have been evaluated from surface tension, viscosity, and refractive index measurements. This persistence of the surface tension (γ) beyond the critical micelle concentration (CMC) appears to suggest that the aggregate formation in the presence of the PEG or PVP or their blends is sufficiently large. The close approximated value of relative viscosity to the unity implies that the conformational changes in the polymer are minimal. The refractive index measurements further reveal that the overall polarizability of the studied systems increases with an increase in the amount of polymer in the solution

Structural analyses of the CRISPR protein Csc2 reveal the RNA-binding interface of the type I-D Cas7 family

<div><p>Upon pathogen invasion, bacteria and archaea activate an RNA-interference-like mechanism termed CRISPR (clustered regularly interspaced short palindromic repeats). A large family of Cas (CRISPR-associated) proteins mediates the different stages of this sophisticated immune response. Bioinformatic studies have classified the Cas proteins into families, according to their sequences and respective functions. These range from the insertion of the foreign genetic elements into the host genome to the activation of the interference machinery as well as target degradation upon attack. Cas7 family proteins are central to the type I and type III interference machineries as they constitute the backbone of the large interference complexes. Here we report the crystal structure of <i>Thermofilum pendens</i> Csc2, a Cas7 family protein of type I-D. We found that Csc2 forms a core RRM-like domain, flanked by three peripheral insertion domains: a lid domain, a Zinc-binding domain and a helical domain. Comparison with other Cas7 family proteins reveals a set of similar structural features both in the core and in the peripheral domains, despite the absence of significant sequence similarity. <i>T. pendens</i> Csc2 binds single-stranded RNA in vitro in a sequence-independent manner. Using a crosslinking - mass-spectrometry approach, we mapped the RNA-binding surface to a positively charged surface patch on <i>T. pendens</i> Csc2. Thus our analysis of the key structural and functional features of <i>T. pendens</i> Csc2 highlights recurring themes and evolutionary relationships in type I and type III Cas proteins.</p></div