No abstract

Developing eco‐friendly, nonirritant, low‐toxic, and high‐efficient surface active ingredients for detergents is an ongoing challenge in the detergent field. Surfactin is one of the representative lipopeptides produced by microorganisms. In this article, we report the surfactin isolated from cell‐free broth of Bacillus subtilis HSO121 and purified by reversed‐phase high‐performance liquid chromatography for detergent formulations. The biodegradability, acute dermal irritation, acute oral toxicity (LD50 and LC50), surface activity, washing efficiency, and compatibility with hard water of the purified biosurfactant surfactin have been studied to explore the feasibility for applications of the surfactin in detergents. Acute oral toxicity tests (LD50 > 5000 mg kg−1, LC50 > 1000 mg kg−1) and skin irritation tests (PII = 0) indicate that the surfactin is a low‐toxic and nonirritant ingredient for detergent formulation. Moreover, the surfactin shows excellent surface and interfacial properties of emulsification and wettability, high compatibility, and stability in a wide range of temperatures, pH, and hard water and acceptable properties in biodegradability and foaming ability, which suggests that the biosurfactant surfactin is a promising ingredient for detergent formations in our daily life and for industrial applications.

The generation of mechanical forces are central to a wide range of vital biological processes, including the function of the cytoskeleton. Although the forces emerging from the polymerization of native proteins have been studied in detail, the potential for force generation by aberrant protein polymerization has not yet been explored. Here, we show that the growth of amyloid fibrils, archetypical aberrant protein polymers, is capable of unleashing mechanical forces on the piconewton scale for individual filaments. We apply microfluidic techniques to measure the forces released by amyloid growth for two systems: insulin and lysozyme. The level of force measured for amyloid growth in both systems is comparable to that observed for actin and tubulin, systems that have evolved to generate force during their native functions and, unlike amyloid growth, rely on the input of external energy in the form of nucleotide hydrolysis for maximum force generation. Furthermore, we find that the power density released from growing amyloid fibrils is comparable to that of high-performance synthetic polymer actuators. These findings highlight the potential of amyloid structures as active materials and shed light on the criteria for regulation and reversibility that guide molecular evolution of functional polymers.microfluidics | amyloidosis | active materials | biological force generation | protein misfolding

Elucidation of the fundamental interactions of proteins with biological membranes under native conditions is crucial for understanding the molecular basis of their biological function and malfunction. Notably, the large surface to volume ratio of living cells provides a molecular landscape for significant interactions of cellular components with membranes, thereby potentially modulating their function. However, such interactions can be challenging to probe using conventional biophysical methods due to the heterogeneity of the species and processes involved. Here, we use direct measurements of micron scale molecular diffusivity to detect and quantify the interactions of α-synuclein, associated with the etiology of Parkinson's disease, with negatively charged lipid vesicles. We further demonstrate that this microfluidic approach enables the characterization of size distributions of different binary mixtures of vesicles, which are not readily accessible using conventional light scattering techniques. Finally, the size distributions of the two α-synuclein conformations, free α-synuclein and membrane-bound α-synuclein, were resolved under varying lipid:protein ratios, thus, allowing the determination of the dissociation constant and the binding stoichiometry associated with this protein-lipid system. The microfluidic diffusional sizing platform allows these measurements to be performed on a time scale of minutes using microlitre volumes, thus, establishing the basis for an approach for the study of molecular interactions of heterogeneous systems under native conditions.

No abstract

Biosurfactant lipopeptide is a promising dispersant over varieties of chemical ones in oil-spill remediation.

Interfacial behavior of surfactin methyl ester derivatives at the n-decane/water interface at low surface coverage has been studied by molecular dynamics simulation. Molecular orientations, structural variability of the peptide ring backbones, interfacial molecular areas, and the motion activities of surfactin derivatives have been determined. The simulations show that surfactin monomethyl ester stands vertically at the oil/water interface compared with surfactin molecule. The aliphatic chains tilt at the interface and can fold back to interact with the hydrophobic amino acid residues within the same molecule. Amino acid residues that the aliphatic chains are favorable to interact with are different between surfactin derivatives. The peptide ring backbones of surfactin and surfactin derivatives expand at the interface. Interfacial molecular areas of surfactin derivatives are all about 110 A(2). Translational and rotational motions of surfactin derivatives are limited at the interface, and the motion activities increase with the hydrophobic character of the peptide moiety.

The surface parameter of protonated surfactin molecules and the structural properties of the protonated surfactin monolayer adsorbed at the air/water interface have been studied by molecular dynamics simulation. The simulation was performed at 293 K and the interfacial concentration of surfactin was set in a range of 0.70-2.20 nm(2) molecule(-1). The results show that the interfacial concentration greatly affects the molecular orientation of surfactin, the structure of the peptide ring backbone and the spatial arrangement of the surfactin monolayer. The peptide ring backbone of the surfactin molecule exhibits a structural flexibility, and a more packed structure is adopted at higher interfacial concentration. The hydrophobic contacts between surfactin molecules and the stability of the secondary structures, β-turn structure in Leu2 → Asp5 and the β-sheet domains, are enhanced when the surfactin molecules are in a very packed situation.