Physisorption of enzymatically active chymotrypsin on titania colloidal particles

pH-Dependent Changes in Structural Stabilities of Bt Cry1Ac Toxin and Contrasting Model Proteins following Adsorption on Montmorillonite

The environmental fate of insecticidal Cry proteins, including time-dependent conservation of biological properties, results from their structural stability in soils. The complex cascade of reactions involved in biological action requires Cry proteins to be in solution. However, the pH-dependent changes in conformational stability and the adsorption-desorption mechanisms of Cry protein on soil minerals remain unclear. We used Derjaguin-Landau-Verwey-Overbeek (DLVO) calculation and differential scanning calorimetry to interpret the driving forces and structural stabilities of Cry1Ac and two contrasting model proteins adsorbed by montmorillonite. The structural stability of Cry1Ac is closer to that of the "hard" protein, α-chymotrypsin, than that of the "soft" bovine serum albumin (BSA). The pH-dependent adsorption of Cry1Ac and α-chymotrypsin could be explained by DLVO theory, whereas the BSA adsorption deviated from it. Patch-controlled electrostatic attraction, hydrophobic effects, and entropy changes following protein unfolding on a mineral surface could contribute to Cry1Ac adsorption. Cry1Ac, like chymotrypsin, was partly denatured on montmorillonite, and its structural stability decreased with an increase in pH. Moreover, small changes in the conformational heterogeneity of both Cry1Ac and chymotrypsin were observed following adsorption. Conversely, adsorbed BSA was completely denatured regardless of the solution pH. The moderate conformational rearrangement of adsorbed Cry1Ac may partially explain why the insecticidal activity of Bt toxin appears to be conserved in soils, albeit for a relatively short time period.

Analyzing protein-ligand and protein-interface interactions using high pressure

All protein function is based on interactions with the environment. Proteins can bind molecules for their transport, their catalytic conversion, or for signal transduction. They can bind to each other, and they adsorb at interfaces, such as lipid membranes or material surfaces. An experimental characterization is needed to understand the underlying mechanisms, but also to make use of proteins in biotechnology or biomedicine. When protein interactions are studied under high pressure, volume changes are revealed that directly describe spatial contributions to these interactions. Moreover, the strength of protein interactions with ligands or interfaces can be tuned in a smooth way by pressure modulation, which can be utilized in the design of drugs and bio-responsive interfaces. In this short review, selected studies of protein-ligand and protein-interface interactions are presented that were carried out under high pressure. Furthermore, a perspective on bio-responsive interfaces is given where protein-ligand binding is applied to create functional interfacial structures.

Cavitands Endow All-Dielectric Beads With Selectivity for Plasmon-Free Enhanced Raman Detection of Nε-Methylated Lysine

SiO2/TiO2 microbeads (T-rex) are promising materials for plasmon-free surface-enhanced Raman scattering (SERS), offering several key advantages in biodiagnostics. In this paper we report the combination of T-rex beads with tetraphosphonate cavitands (Tiiii), which imparts selectivity toward Nε-methylated lysine. SERS experiments demonstrated the efficiency and selectivity of the T-rex-Tiiii assays in detecting methylated lysine hydrochloride (Nε-Me-Lys-Fmoc) from aqueous solutions, even in the presence of the parent Lys-Fmoc hydrochloride as interferent. The negative results obtained in control experiments using TSiiii ruled out any other form of surface recognition or preferential physisorption. MALDI-TOF analyses on the beads exposed to Nε-Me-Lys-Fmoc revealed the presence of the Tiiii•Nε-Me-Lys-Fmoc complex. Raman analyses based on the intensity ratio of Nε-Me-Lys-Fmoc and cavitand-specific modes resulted in a dose-response plot, which allowed for estimating the concentration of Nε-methylated lysine from initial solutions in the 1 × 10(-3) to 1 × 10(-5) M range. These results can set the basis for the development of new Raman assays for epigenetic diagnostics.

Bio-waste derived dialdehyde cellulose ethers as supports for α-chymotrypsin immobilization

Enzyme immobilization is an important technique to enhance stability, storability and reusability of enzymes. In the present work, pine needles, a forest bio-waste, were used as a feedstock of cellulose to synthesize new materials as supports for immobilization of α-chymotrypsin (CT) enzyme. The extracted cellulose from pine needles was etherified with different alkyl bromides (RBr) and etherified products were further modified to dialdehyde via oxidation with NaIO4 to get the desired products, dialdehyde cellulose ethers (ROcellCHO). CT was then covalently immobilized onto as-synthesized dialdehyde cellulose ethers via Schiff-base formation, i.e., imine linkage. The synthesized products and enzyme immobilization were confirmed by different characterization techniques and the activity assay of the free and the immobilized CT was carried out using standard protocol with variation of different parameters such as temperature, pH and substrate concentration. The storage stability and reusability of the immobilized CT were also investigated. CT activity was also studied in simulated physiological conditions in the artificial gastric fluid and artificial intestinal fluid. Artificial neural network (ANN) model was employed to correlate the relationship with% relative activity and time, temperature and pH affecting enzyme activity. A good correlation of experimental data was predicted by ANN model.