Improving the activity of immobilized subtilisin by site-specific attachment to surfaces

Understanding the properties of immobilized proteins is critical to the optimal design of biosensors, bioseparations, and bioreactors. The protease subtilisin BPN' was used as a model protein to study how the orientation of immobilized enzyme molecules on surfaces affects their catalytic properties. To achieve this goal, a single cysteine residue was introduced into the cysteine-free enzyme by site-directed mutagenesis. This cysteine residue was designed to be away from the active site of the enzyme. The enzyme molecules were immobilized through the side-chain sulfhydryl group of the cysteine residue on several supports. This site-specific immobilization method leads to ordered two-dimensional arrays of enzyme molecules on the support surface with the active sites of the enzyme oriented toward the solution phase. Such oriented immobilized subtilisin demonstrated a higher catalytic efficiency compared to subtilisin that was immobilized by a conventional method that leads to random immobilization.