Protein engineering applications of industrially exploitable enzymes: Geobacillus stearothermophilus LDH and Candida methylica FDH

Enzymes have become important tools in several industries due to their ability to produce chirally pure and complex molecules with interesting biological properties. The NAD⁺-dependent LDH (lactate dehydrogenase) [bsLDH [Geobacillus stearothermophilus (formerly Bacillus stearothermophilus) LDH] from G. stearothermophilus and the NAD⁺-dependent FDH (formate dehydrogenase) [cmFDH (Candida methylica FDH)] enzyme from C. methylica are particularly crucial enzymes in the pharmaceutical industry and are related to each other in terms of NADH use and regeneration. LDH catalyses the interconversion of pyruvate (oxo acid) and lactate (α-hydroxy acid) using the NADH/NAD⁺ pair as a redox cofactor. Employing LDH to reduce other oxo acids can generate chirally pure α-hydroxy acids of use in the production of pharmaceuticals. One important use of FDH is to regenerate the relatively expensive NADH cofactor that is used by NAD+-dependent oxidoreductases such as LDH. Both LDH and FDH from organisms of interest were previously cloned and overproduced. Therefore they are available at a low cost. However, both of these enzymes show disadvantages in the large-scale production of chirally pure compounds. We have applied two routes of protein engineering studies to improve the properties of these two enzymes, namely DNA shuffling and site-directed mutagenesis. Altering the substrate specificity of bsLDH by DNA shuffling and changing the coenzyme specificity of cmFDH by site-directed mutagenesis are the most successful examples of our studies. The present paper will also include the details of these examples together with some other applications of protein engineering regarding these enzymes.