Characterization of non-covalent immobilized Candida antartica lipase b over PS-b-P4VP as a model bio-reactive porous interface

Hyper-crosslinked Isoporous Block Copolymer Membranes with Robust Solvent Resistance and Customized Pore Sizes for Precise Separation

Isoporous block copolymer membranes are viewed as the next-generation separation membranes for their unique structures and urgent application in precise separation. However, an obvious weakness for such membranes is their poor solvent-resistance which limits their applications to aqueous solution, and isoporous membranes with superior solvent-resistance and tunable pore size have been rarely prepared before. Herein, self-supporting isoporous membranes with excellent solvent resistance are prepared by the facile yet robust hyper-crosslinking approach which is able to create a rigid network in whole membranes. The hyper-crosslinking is found to be a novel and non-destructive approach that does not change pore size and isoporous structure during the reaction, and the resulting hyper-crosslinked isoporous membranes display superior structural and separation stability to a broad range of solvents with varied polarities for months to years. More importantly, hyper-crosslinking has proved to be a universal strategy that is applicable to isoporous membranes with varied pore size and pore chemistry, offering an important opportunity to prepare solvent-resistant isoporous membranes with customizable pore size and pore functionality that are important to realize their accurate separations in organic solvents. This concept is demonstrated finally by precise and on-demand separation of nanoparticles with the prepared membranes.

The Conformational Transitions and Dynamics of Burkholderia cepacia Lipase Regulated by Water-Oil Interfaces

Structural dynamics and conformational transitions are crucial for the activities of enzymes. As one of the most widely used industrial biocatalysts, lipase could be activated by the water-oil interfaces. The interface activations were believed to be dominated by the close-to-open transitions of the lid subdomains. However, the detailed mechanism and the roles of structure transitions are still under debate. In this study, the dynamic structures and conformational transitions of Burkholderia cepacia lipase (LipA) were investigated by combining all-atom molecular dynamics simulations, enhanced sampling simulation, and spectrophotometric assay experiments. The conformational transitions between the lid-open and lid-closed states of LipA in aqueous solution are directly observed by the computational simulation methods. The interactions between the hydrophobic residues on the two lid-subdomains are the driven forces for the LipA closing. Meanwhile, the hydrophobic environment provided by the oil interfaces would separate the interactions between the lid-subdomains and promote the structure opening of LipA. Moreover, our studies demonstrate the opening of the lids structure is insufficient to initiate the interfacial activation, providing explanations for the inability of interfacial activation of many lipases with lid structures.

The influence of calcium ions (Ca2+) on the enzymatic hydrolysis of lipopolysaccharide aggregates to liberate free fatty acids (FFA) in aqueous solution

The chemical environment in aqueous solutions greatly influences the ability of amphiphilic molecules such as lipopolysaccharides (LPS) to aggregate into different structural phases in aqueous solutions. Understanding the substrate's morphology and conditions of aqueous solution that favor both enzymatic activity and the disruption of LPS aggregates are crucial in developing agents that can counteract the new trend of multidrug resistance by gram-negative bacteria. In this study, we developed two LPS morphologies using LPS from Escherichia coli as a model to study the in vitro hydrolytic response when using a lipase treatment. The hydrolysis was performed using lipase b from Candida antarctica to understand the catalytic effect in removing fatty acids from its lipid A moiety on different LPS aggregates. Physical and chemical characterizations of the products included dynamic light scattering, small angle X-ray scattering, Fourier transform infrared spectroscopy, thin-layer chromatography, and gas chromatography. Our results suggest a trend of prominent hydrolytic response (72% enhancement) upon the addition of calcium ions to induce LPS aggregates into bilayer formations. Moreover, our results revealed the detection of myristic acid (C14:0) as the product of the hydrolysis when using RaLPS in its aggregate forms.