Nature Versus Nurture: Developing Enzymes That Function Under Extreme Conditions

Abstract

Many industrial processes used to produce chemicals and pharmaceuticals would benefit from enzymes that function under extreme conditions. Enzymes from extremophilic microorganisms have evolved to function in a variety of extreme environments, and bioprospecting for these microorganisms has led to the discovery of new enzymes with high tolerance to nonnatural conditions. However, bioprospecting is inherently limited by the diversity of enzymes evolved by nature. Protein engineering has also been successful in generating extremophilic enzymes by both rational mutagenesis and directed evolution, but screening for activity under extreme conditions can be difficult. This review examines the emerging synergy between bioprospecting and protein engineering in developing extremophilic enzymes. Specific topics include unnatural industrial conditions relevant to biocatalysis, biophysical properties of extremophilic enzymes, and industrially relevant extremophilic enzymes found either in nature or through protein engineering. 77 Annu. Rev. Chem. Biomol. Eng. 2012.3:77-102. Downloaded from www.annualreviews.org by University of Toronto on 11/15/12. For personal use only. Click here for quick links to Annual Reviews content online, including: • Other articles in this volume • Top cited articles • Top downloaded articles • Our comprehensive search Further ANNUAL REVIEWS T opt : optimum activity temperature 78 Liszka et al. Annu. Rev. Chem. Biomol. Eng. 2012.3:77-102. Downloaded from www.annualreviews.org by University of Toronto on 11/15/12. For personal use only. www.annualreviews.org • Enzymes Under Extreme Conditions 79 Annu. Rev. Chem. Biomol. Eng. 2012.3:77-102. Downloaded from www.annualreviews.org by University of Toronto on 11/15/12. For personal use only.greater potential for success. The answer to this question is not obvious and may depend strongly on the conditions required, the desired enzymatic reaction, and the type of enzyme used. EXTREME CONDITIONS RELEVANT TO INDUSTRIAL PROCESSES Conditions Found in NatureMicroorganisms exist in very different environments, and their enzymes and proteins have adapted to extreme temperatures, pressures, alkalinity/acidity, and/or osmolarity. Many of these extreme conditions mimic those found in industrial processes that currently employ enzymes or stand to benefit from them. Nature, therefore, is an abundant source of enzymes and proteins tolerant to extreme conditions. Extreme temperatures. Performing enzyme reactions at elevated temperatures has several potential advantages including higher substrate solubility, faster reaction rates, reduced risk of system contamination, lower solution viscosity, and increased solvent miscibility. However, there are many examples of enzymes used in processes that operate at lower temperatures as well, such as cold-active hydrolytic enzymes used in laundry detergents or for cleaning animal hides, proteases used for cleaning contact lenses, and pectinases for clarifying and extracting fruit juices (9). Mesophilic enzymes are less effective at...

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