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The area of biocatalysis itself is in rapid development, fueled by both an enhanced repertoire of protein engineering tools and an increasing list of solved problems. Biocatalysts, however, are delicate materials that hover close to the thermodynamic limit of stability. In many cases, they need to be stabilized to survive a range of challenges regarding temperature, pH value, salt type and concentration, co-solvents, as well as shear and surface forces. Biocatalysts may be delicate proteins, however, once stabilized, they are efficiently active enzymes. Kinetic stability must be achieved to a level satisfactory for large-scale process application. Kinetic stability evokes resistance to degradation and maintained or increased catalytic efficiency of the enzyme in which the desired reaction is accomplished at an increased rate. However, beyond these limitations, stable biocatalysts can be operated at higher temperatures or co-solvent concentrations, with ensuing reduction in microbial contamination, better solubility, as well as in many cases more favorable equilibrium, and can serve as more effective templates for combinatorial and data-driven protein engineering. To increase thermodynamic and kinetic stability, immobilization, protein engineering, and medium engineering of biocatalysts are available, the main focus of this work. In the case of protein engineering, there are three main approaches to enhancing the stability of protein biocatalysts: (i) rational design, based on knowledge of the 3D-structure and the catalytic mechanism, (ii) combinatorial design, requiring a protocol to generate diversity at the genetic level, a large, often high throughput, screening capacity to distinguish 'hits' from 'misses', and (iii) data-driven design, fueled by the increased availability of nucleotide and amino acid sequences of equivalent functionality. |
