Structural Insights into Short Chain (SDR) and Medium Chain (MDR) families of Alcohol Dehydrogenases for Biocatalytic Applications

Current abiotic synthesis is very effective in yielding enantiomerically pure compounds with high yields, however the route taken may not be very efficient nor green with the use of solvents, heavy metals and toxic chemicals. Alcohol dehydrogenases (ADHs) are industrially useful biocatalysts in providing synthetically useful building blocks or chiral alcohols as flavour or fragrance chemicals. In this thesis, the X-ray crystal structures have been determined for the ADHs from Ralstonia sp. (RasADH), Sphingobium yanoikuyae (SyADH), Thermus sp. (TADH) and Candida parapsilosis (CPCR2). Datasets for the apo- and NADPH complex for the gene encoding RasADH, an ADH from the short-chain family, from Ralstonia sp. DSM 6428 were obtained at 1.5 Å and 2.9 Å respectively. The models for the apo- and NADPH complex were refined to Rcryst/Rfree values of 15.8%/18.8% and 26.8%/29.3% respectively. The dataset for the gene encoding SyADH, an ADH from the short-chain family, from Sphingobium yanoikuyae DSM 6900 in complex with NADPH was obtained at 2.5 Å. The model was refined to an Rcryst/Rfree value of 23.4%/25.1%. The dataset for the gene encoding TADH, an ADH from the medium-chain family, from Thermus sp. ATN1 was obtained at 2.7 Å with three of four active sites in complex with NADH. The model was refined to an Rcryst/Rfree value of 19.6%/24.6%. The dataset for the gene encoding CPCR2, an ADH from the medium-chain family, from Candida parapsilosis DSM 70125 was obtained at 2.0 Å in complex with NADH. The model was refined to an Rcryst/Rfree value of 20.5%/24.1%. These crystal structures provide a robust platform for rational engineering to improve the enzymes’ substrate specificity, enantioselectivity, thermostability and solvent tolerance. As such, ADHs as biocatalysts will inevitably provide a greener alternative for the synthesis of chiral alcohols over abiotic synthesis.