AOT/isooctane reverse micelles with a microaqueous core act as protective shells for enhancing the thermal stability of Chromobacterium viscosum lipase

Deciphering the Nanoconfinement Effect on the Folding Pathway of c-MYC Promoter-Based Intercalated-Motif DNA by Single-Molecule Förster Resonance Energy Transfer

Intercalated-motif (i-motif) DNA formed by cytosine (C)-rich sequences has been considered a novel target in anticancer research. Interestingly, this type of noncanonical DNA structure is highly dynamic and can display several conformational polymorphisms based on the immediate surrounding environment. However, studies regarding the folding pathway of i-motifs having disease-specific sequences under a confined environment at physiological pH are relatively scarce. This thereby warrants more explorations that will decipher their structural and functional properties inside constrained media. Herein, using the single-molecule Förster Resonance Energy Transfer (smFRET) studies, for the first time, we have illustrated the conformational dynamics of c-MYC promoter-based i-motif structures at physiological pH inside microemulsions of different dimensions. We concluded that the folding of such motifs under confined space is not a direct transition between the random coil and i-motif conformations; rather it occurs through a partially folded intermediate, depending on the confined dimension.

The effect of single CNTs/GNPs and complexes on promoting the interfacial catalytic activity of lipase in conventional emulsions

BACKGROUND

The interfacial activation mechanism of lipase enables it to exhibit high catalytic activity in water-in-oil (W/O) microemulsions. However, W/O microemulsions have obvious defects such as a small water pool and a large demand for surfactants. The present study investigated the substitutability of conventional oil-in-water (O/W) and W/O emulsions as lipase catalytic systems. Carbon nanotubes (CNTs)/gold nanoparticles (GNPs) or CNT-GNP electrostatically bonded complexes were added into the conventional emulsion system.

RESULTS

The simulated biphasic system and fluorescence study showed different and even contradictory results for the interfacial behavior of CNTs and CNT-GNP complexes due to the variation of the dispersibility of CNTs in cetyltrimethylammonium bromide (CTAB). Results also showed that conventional O/W emulsions were more suitable for lipase catalysis than conventional W/O emulsions. When CNTs or CNT_CATB -GNP complexes were added in a conventional O/W emulsion system, the catalytic activity of lipase was significantly promoted (up to 4.8-fold using CNTs and 3.5-fold using CNT_CATB -GNP complexes compared with free lipase).

CONCLUSIONS

The possible reason for this promotion may be due to the increase in the interface area. The current study was not only the latest exploration of lipase activity promotion via nanomaterials, but also explored a new lipase catalytic system and provides further insight into improving the catalytic performance of lipase in conventional emulsions. © 2020 Society of Chemical Industry.

Effect of intense pulsed light on the deactivation of lipase: Enzyme-deactivation kinetics and tertiary structural changes by fragmentation

The effect of intense pulsed light (IPL) irradiation on Chromobacterium viscosum lipase was investigated with a primary focus on catalytic activity and molecular structure. During IPL irradiation, lipase activity decreased significantly with increasing pulse fluence (F_p) and exposure time (t_e). IPL-induced deactivation kinetics were further elucidated based on a two-step series-type deactivation model (constant deactivation rate k₁ >k₂). F_p was found to be the dominant variable affecting the degree of lipase deactivation, and residual activity was not associated with increasing t_e below a certain F_p energy density (2.66 mJ/cm²), implying a critical threshold for IPL-induced deactivation of lipase. From the results of fluorescence spectroscopy and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), we determined that IPL-induced deactivation was caused by fragmentation, leading to lipase tertiary structural changes. Furthermore, the results of FindPept analysis and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) indicated that the internal sensitive bonds of lipase were cleaved preferentially by IPL, such that IPL irradiation induced site-sensitive fragmentation and peptide bond cleavage.

Optimization of AOT reversed micelle forward extraction of 7S globulin subunits from soybean proteins

The work attempted to study on separating the α', α and β subunits of 7S globulin from soybean proteins by reverse micelles. The effects of six single factors (W0, time, temperature, pH, surfactant concentration and salt solution species) on three subunit partitioning were discussed. The main influence factors (time, temperature and surfactant concentration) were optimized by the response surface test (Box-Behnken design, three factor three level) in order to optimize the forward extracting three subunits of 7S globulin. It was observed that the independent factor had substantial effect on the forward extraction yield of three subunits of 7S globulin. The statistical analysis showed that the reverse micelles could significantly affect the forward extraction efficiency of protein subunits. The highest forward extraction efficiency of α', α and β subunits achieved 78.21, 63.65 and 61.34%, respectively. The proposed method also showed that the forward extraction efficiency of subunits with larger molecular weight was higher than low molecular weight.

Selective production of 1-monocaprin by porcine liver carboxylesterase-catalyzed esterification: Its enzyme kinetics and catalytic performance

Porcine liver carboxylesterase (PLE) belongs to carboxylesterase family (EC 3.1.1.1) as a serine-type esterase. The PLE-catalyzed esterification of capric acid with glycerol in reverse micelles was investigated on the catalytic performance and enzyme kinetics. The most suitable structure of reverse micelles was comprised of isooctane (reaction medium) and bis(2-ethylhexyl) sodium sulfosuccinate (AOT, anionic surfactant) with 0.1 of R-value ([water]/[surfactant]) and 3.0 of G/F-value ([glycerol]/[fatty acid]) for the PLE-catalyzed esterification. In the aspect of regio-selectivity, the PLE mainly produced 1-monocaprin without any other products (di- and/or tricaprins of subsequent reactions). Furthermore, the degree of esterification at equilibrium state (after 4 h from the initiation) was 62.7% under the optimum conditions at pH 7.0 and 60 °C. Based on Hanes-Woolf plot, the apparent Km and Vmax values were calculated to be 16.44 mM and 38.91 μM/min/mg protein, respectively.