Enzymology of Xylose Utilization in Yeast

Xylose is a major constituent sugar of the polysaccharide fraction of plant biomass. Forestry and agriculture produce huge annual amounts of xylose equivalents as waste products that are not well utilized at the present time. Micro-organisms are capable of producing a range of value-added chemicals from xylose. The biological conversion of xylose into ethanol is most interestig considering the exploitation of renewable resources for car fuel production. Baker`s yeast is a well known producer of ethanol and its current process technology reflects a decades-long optimization, step by step. Unfortunately, baker`s yeast cannot utilize xylose because it lacks the metabolic components required. An important goal of research worldwide is, therefore, to generate an engineered baker`s yeast with improved metabolic capabilities. Metabolic engineering on the basis of modern gene technology is promising means of accomplishing this ambitious task. Detailed knowledge of structure-function relationships of key enzymes involved in xylose utilisation, namely xylose reductase and xylitol dehydrogenase, is of paramount importance to design and finely tune xylose metabolism. Understanding the function of these enzymes within the context of the cellular environment is another major issue. This project has provided novel insights into how xylose reductase and xylitol dehydrogenase work and shown routes for modification of the properties of the enzymes, particularly xylose reductase. The experimental approach has been a multidisciplinary one which included biochemistry, biotechnology, structural chemistry, and organic chemistry in national and international collaborations.