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, Tm, the affinity of the fluorescent probe to the binding site, Kd, and the rate constant, kcat, 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

Specific anion effect on properties of HRV 3C protease.

Specific salts effect is intensively studied from the prospective of modification of different physico-chemical properties of biomacromolecules. Limited knowledge of the specific salts effect on enzymes led us to address the influence of five sodium anions: sulfate, phosphate, chloride, bromide, and perchlorate, on catalytic and conformational properties of human rhinovirus-14 (HRV) 3C protease. The enzyme conformation was monitored by circular dichroism spectrum (CD) and by tyrosines fluorescence. Stability and flexibility of the enzyme have been analyzed by CD in the far-UV region, differential scanning calorimetry and molecular dynamics simulations, respectively. We showed significant influence of the anions on the enzyme properties in accordance with the Hofmeister effect. The HRV 3C protease in the presence of kosmotropic anions, in contrast with chaotropic anions, exhibits increased stability, rigidity. Correlations of stabilization effect of anions on the enzyme with their charge density and the rate constant of the enzyme with the viscosity B-coefficients of anions suggest direct interaction of the anions with HRV 3C protease. The role of stabilization and decreased fluctuation of the polypeptide chain of HRV 3C protease on its activation in the presence of kosmotropic anions is discussed within the frame of the macromolecular rate theory.

Hofmeister effect on catalytic properties of chymotrypsin is substrate-dependent.

Effect of Hofmeister sodium salts, sulfate, chloride, bromide and perchlorate, on catalytic properties and stability of chymotrypsin has been studied by absorbance and circular dichroism spectroscopies. To address Hofmeister effect on activity of chymotrypsin, two different substrates, N-benzoyl-L-tyrosine ethyl ester and amide N-succinyl-L-phenylalanine-p-nitroanilide, were used. Catalytic activity of chymotrypsin is dependent on salt concentration and position of anion in Hofmeister series. The enzyme activity for both substrates is only slightly affected by chaotropic anions and increases with kosmotropic nature of anions. While the trend of Hofmeister effect on chymotrypsin catalysis is similar for both substrates, the amplitude of the effect significantly differs. In the presence of 1 M sulfate, catalytic efficiency increased by ~2-fold for the ester but ~20-fold for the amide substrate. Positive correlation between stability and activity of chymotrypsin indicates the interdependence of these enzyme properties and is in agreement with recently developed macromolecular rate theory suggesting an important role of protein dynamics in enzyme catalysis. Linear dependencies of catalytic properties of chymotrypsin with partitioning of anions at bulk water/air as well as at hydrocarbon surface strongly indicate that the modulated enzyme properties are results of direct interaction of anions with protein surface.

Correlation of lysozyme activity and stability in the presence of Hofmeister series anions.

Enzymatic activity and stability of lysozyme in the presence of salts have been studied by fluorescence spectroscopy and differential scanning calorimetry, respectively. The effect of sodium salts of sulfate, acetate, chloride, bromide, thiocyanate, and perchlorate on lysozyme properties depends on anion concentration as well as on position of anion in the Hofmeister series. Kosmotropic anions (sulfate and acetate) increase stability and activate the enzyme while chaotropic anions (bromide, thiocyanate and perchlorate) including chloride decrease stability and inhibits the enzyme activity. Strong correlation between stability and activity of lysozyme suggest the interdependence of these enzyme properties in the presence of salts. The fact that the properties of lysozyme correlate with partition coefficients of anions at hydrocarbon surface clearly indicates that Hofmeister effect of anions is mediated by their interactions with nonpolar parts of the enzyme surface despite its high positive net charge at studied conditions. The efficiency of the anions in affecting both activity and stability of lysozyme also correlates with other anion-related parameters most notably with polarizability of monovalent anions. The presented work points to a critical role of interaction of anions with nonpolar protein surface for the Hofmeister effect. Moreover, the simultaneous investigation of protein stability and activity, in the relation with the Hofmeister effect, provides important information regarding stability/rigidity of enzyme structure for its catalytic activity.