Mechanisms of thermal stability adopted by thermophilic proteins and their use in white biotechnology

Considerable interest has been generated in the mechanism which nature utilises to increase the stability of enzymes found in thermophilic and hyperthermophilic species. This has been the subject of many reviews, and our understanding has been enhanced by the increasing number of high-resolution thermostable enzyme structures that have been determined. Different species of bacteria and Archaea have used different mechanisms to achieve stability. A comparative approach has been used to carry out a detailed study of specific enzymes from a range of organisms in order to understand acquired stability at a structural level. This chapter will discuss the rules to increase protein thermostability that have been obtained from protein structural studies that are currently available. It will also examine other ways to stabilise existing proteins by lessons learnt from nature and by protein immobilisation. Thermostable enzymes find applications in "white biotechnology" including the biosynthesis of fine chemicals. This chapter will discuss specific examples of thermophilic enzymes already adopted for industrial applications. These include alcohol dehydrogenases for chiral alcohol production, aminoacylases for optically pure amino acids and amino acid analogues, transaminases for chiral amine production and gamma-lactamases for chiral gamma-lactam building blocks which are subsequently incorporated into carbocyclic nucleotides. A brief overview of other applications in biorefining, biofuel cells and detergents are also presented.