Hyperactivation of α-chymotrypsin by the Hofmeister effect

Improving the catalytic activity of β-glucosidase from Coniophora puteana via semi-rational design for efficient biomass cellulose degradation

In order to improve the degradation activity of β-glucosidase (CpBgl) from Coniophora puteana, the structural modification was conducted. The enzyme activity of mutants CpBgl-Q20C and CpBgl-A240S was increased by 65.75% and 58.58%, respectively. These mutants exhibited maximum activity under the same conditions as wild-type CpBgl (65 ℃ and pH 5.0), slightly improved stabilities compared that of the wild-type, and remarkably enhanced activities in the presence of Mn²⁺ or Fe²⁺. The V_max of CpBgl-Q20C and CpBgl-A240S was increased to 138.18 and 125.14 μmol/mg/min, respectively, from 81.34 μmol/mg/min of the wild-type, and the catalysis efficiency (k_cat/K_m) of CpBgl-Q20C (335.79 min^-1/mM) and CpBgl-A240S (281.51 min^-1/mM) was significantly improved compared with that of the wild-type (149.12 min^-1/mM). When the mutant CpBgl-Q20C were used in the practical degradation of different biomasses, the glucose yields of filter paper, corncob residue, and fungi mycelia residue were increased by 17.68%, 25.10%, and 20.37%, respectively. The spatial locations of the mutation residues in the architecture of CpBgl and their unique roles in the enzyme-substrate binding and catalytic efficiency were probed in this work. These results laid a foundation for evolution of other glycoside hydrolases and the industrial bio-degradation of cellulosic biomass in nature.

Modulation of global stability, ligand binding and catalytic properties of trypsin by anions

Specific salts effect is well-known on stability and solubility of proteins, however, relatively limited knowledge is known regarding the effect on catalytic properties of enzymes. Here, we examined the effect of four sodium anions on thermal stability and catalytic properties of trypsin and binding of the fluorescent probe, p-aminobenzamidine (PAB), to the enzyme. We show that the specific anions effect on trypsin properties agrees with the localization of the anions in the Hofmeister series. Thermal stability of trypsin, T_m, the affinity of the fluorescent probe to the binding site, K_d, and the rate constant, k_cat, of trypsin-catalyzed hydrolysis of the substrate N-benzoyl-L-arginine ethyl ester (BAEE) increase with increasing kosmotropic character of anions in the order: perchlorate<bromide<chloride<sulfate, while the value of Michaelis constant, K_M, decreases. Correlations between the values of T_m, K_d for PAB, k_cat, and K_M for BAEE in the presence of 1 M studied salts suggest interrelation among these parameters of the enzyme. Global stabilization as well as increased rigidity of trypsin is accompanied by strengthening of interaction with fluorescent probe PAB and in accordance with decreasing values of K_M for the substrate BAEE. Strong correlations between parameters characterizing the trypsin properties with the charge densities of anions clearly indicate direct electrostatic interaction as a basis of the specific anion effect on the conformational and functional properties of the enzyme.

Opalescence Arising from Network Assembly in Antibody Solution

Opalescence of therapeutic antibody solutions is one of the concerns in drug formulation. However, the mechanistic insights into the opalescence of antibody solutions remain unclear. Here, we investigated the assembly states of antibody molecules as a function of antibody concentration. The solutions of bovine gamma globulin and human immunoglobulin G at around 100 mg/mL showed the formation of submicron-scale network assemblies. The network assembly resulted in the appearance of opalescence with a transparent blue color without the precipitates of antibodies. Furthermore, the addition of trehalose and arginine, previously known to act as protein stabilizers and protein aggregation suppressors, was able to suppress the opalescence arising from the network assembly. These results will provide an important information for evaluating and improving protein formulations.

Perchlorate Salts Exert a Dominant, Deleterious Effect on the Structure, Stability, and Activity of α-Chymotrypsin

The presence of perchlorate ions on Mars raises the question of how these ions influence the biochemistry of any contaminant life introduced into the martian environment, or what selection pressures perchlorate ions exert on any environment that contains these ions, such as the Atacama Desert. In this study, we investigated the structure, stability, and enzyme activity of the model enzyme α-chymotrypsin in the presence of five Mars relevant salts, MgSO₄, MgCl₂, Mg(ClO₄)₂, Ca(ClO₄)₂, and NaClO₄. We found that all the perchlorate salts reduced the enzyme activity of α-chymotrypsin in a concentration-dependent manner, with Mg(ClO₄)₂ and Ca(ClO₄)₂ having the greatest effect. This observation extends to our structural studies, which show that 1 M Mg(ClO₄)₂ and Ca(ClO₄)₂ greatly alter the tertiary structural environment of α-chymotrypsin. We also found that all the perchlorate salts assayed reduced the melting temperature of α-chymotrypsin, whereas the sulfate and chloride salts were able to increase the protein melting temperature. We also demonstrated that a brine containing both perchlorate and sulfate ions exerts the same deleterious effects on α-chymotrypsin's melting temperature and enzyme activity as that of a perchlorate-only brine. This suggests that the perchlorate salts exert a dominant, deleterious effect on protein biochemistry. These results indicate that although perchlorate salts are beneficial to the presence of liquid water due to low eutectic points, they also hamper the habitability of their own environment. Life in such brines would, therefore, have to adapt its cellular machinery to the perchlorate ion's presence or find a way of excluding it from said machinery.

Flow-through enzymatic reactors using polymer monoliths: From motivation to application

The application of monolithic materials as carriers for enzymes has rapidly expanded to the realization of flow-through analysis and bioconversion processes. This expansion is partly attributed to the absence from diffusion limitation in many monoliths-based enzyme reactors. Particularly, the relatively ease of introducing functional groups renders polymer monoliths attractive as enzyme carriers. After summarizing the motivation to develop enzymatic reactors using polymer monoliths, this review reports the most recent applications of such reactors. Besides, the present review focuses on the crucial characteristics of polymer monoliths affecting the immobilization of enzymes and the processing parameters dictating the performance of the resulting enzymatic reactors. This review is intended to provide a guideline for designing and applying flow-through enzymatic reactors using polymer monoliths.

Traversing the Red-Green-Blue Color Spectrum in Rationally Designed Cupredoxins

Blue copper proteins have a constrained Cu(II) geometry that has proven difficult to recapitulate outside native cupredoxin folds. Previous work has successfully designed green copper proteins which could be tuned blue using exogenous ligands, but the question of how one can create a self-contained blue copper site within a de novo scaffold, especially one removed from a cupredoxin fold, remained. We have recently reported a red copper protein site within a three helical bundle scaffold which we later revisited and determined to be a nitrosocyanin mimic, with a CuHis₂CysGlu binding site. We now report efforts to rationally design this construct toward either green or blue copper chromophores using mutation strategies that have proven successful in native cupredoxins. By rotating the metal binding site, we created a de novo green copper protein. This in turn was converted to a blue copper protein by removing an axial methionine. Following this rational sequence, we have successfully created red, green, and blue copper proteins within an alpha helical fold, enabling comparisons for the first time of their structure and function disconnected from the overall cupredoxin fold.

Refining the model to design α-chymotrypsin superactivators: the role of the binding mode of quaternary ammonium salts

Modelling, synthesis and kinetic studies were combined to investigate the interactions responsible for the superactivation of α-chymotrypsin by ammonium-based additives.