Purification of His-tagged proteins using Ni2+–poly(2-acetamidoacrylic acid) hydrogel

Equilibrium adsorption of hexahistidine on pH-responsive hydrogel nanofilms

We present a molecular theory to study the adsorption of different species within pH-sensitive hydrogel nanofilms. The theoretical framework allows for a molecular-level description of all the components of the system, and it explicitly accounts for the acid-base equilibrium. We concentrate on the adsorption of hexahistidine, one of the most widely used tags in bio-related systems, particularly in chromatography of proteins. The adsorption of hexahistidine within a grafted polyacid hydrogel film shows a nonmonotonic dependence on the solution pH. Depending on the salt concentration, the density of the polymer network, and the bulk concentration of peptide, substantial adsorption is predicted in the intermediate pH range where both the network and the amino acids are charged. To enhance the electrostatic attractions, the acid-base equilibrium of adsorbed hexahistidine is shifted significantly, increasing the degree of charge of the residues as compared to the bulk solution. Such a shift depends critically on the conditions of the environment at the nanoscale. At the same time, the degree of dissociation of the network becomes that of the isolated acid group in a dilute solution, which means that the network is considerably more charged than when there is no adsorbate molecules. This work provides fundamental information on the physical chemistry behind the adsorption behavior and the response of the hydrogel film. This information can be useful in designing new materials for the purification or separation/immobilization of histidine-tagged proteins.

Radiofrequency treatment enhances the catalytic function of an immobilized nanobiohybrid catalyst

Biocatalysis, the use of enzymes in chemical transformation, has undergone intensive development for a wide range of applications. As such, maximizing the functionality of enzymes for biocatalysis is a major priority to enable industrial use. To date, many innovative technologies have been developed to address the future demand of enzymes for these purposes, but maximizing the catalytic activity of enzymes remains a challenge. In this study, we demonstrated that the functionality of a nanobiocatalyst could be enhanced by combining immobilization and radiofrequency (RF) treatment. Aminopeptidase PepA-encapsulating 2 nm platinum nanoparticles (PepA-PtNPs) with the catalytic activities of hydrolysis and hydrogenation were employed as multifunctional nanobiocatalysts. Immobilizing the nanobiocatalysts in a hydrogel using metal chelation significantly enhanced their functionalities, including catalytic power, thermal-stability, pH tolerance, organic solvent tolerance, and reusability. Most importantly, RF treatment of the hydrogel-immobilized PepA-PtNPs increased their catalytic power by 2.5 fold greater than the immobilized PepA. Our findings indicate that the catalytic activities and functionalities of PepA-PtNPs are greatly enhanced by the combination of hydrogel-immobilization and RF treatment. Based on our findings, we propose that RF treatment of nanobiohybrid catalysts immobilized on the bulk hydrogel represents a new strategy for achieving efficient biocatalysis.