Helena Taberman

University of Eastern Finland, Joensuu Campus
Supervisor: Juha Rouvinen
Funding: ISB
Date: 2012-01-01

Structure-function studies on carbohydrate modifying enzymes potential for plant biomass conversion routes

Sustainable (or Green) chemistry represent a rapidly developing research and industrial area where the goal is to substitute renewable resources for petroleum-based feedstocks to produce high-quality products and materials with the help of environmentally benign (bio)chemical catalysts. Metabolic engineering can be used to construct new microbial strains for more efficient conversion of e.g. biomass sugars into organic acids, which are important platform compounds, for chemical syntheses for various applications and polymerisation into new biopolymers (polyesters, polyamides) with novel properties (Sauer et al. (2008) Trends Biotechnol. 26, 100).

Cellulose, composed of beta-glucose units, is the most common polysaccharide in plant biomass and its use in pulp and paper industry has long traditions. Glucose, derived from cellulose, is also currently being studied by many research groups worldwide as a source for production of biofuels and biochemicals. Other polysaccharide components of biomass, hemicellulose and pectin, have been less used and considered usually as waste material. However, these polysaccharides are structurally less solid and consequently their enzymatic utilization is easier. Microbial pathways exist for carbohydrate catabolism of hemicellulose-based sugars; these include D-glucuronic acid, D-xylose and L-arabinose pathways. Many of the enzymes involved in these pathways are oxidoreductases containing NAD(P) as a cofactor,or dehydratases having usually a divalent cation in the active site. It is surprising that relatively little is known, both in terms of structure and function, of many of these enzymes.

In this research project the goal is to determine crystal structures of four different key enzymes (L-Arabonate dehydratase, D-Xylose oxidoreductase, D-Galactarolactone cycloisomerase, and Keto-deoxy-D-galactarate dehydratase) involved in carbohydrate catabolism of biomass-derived sugars, and furthermore study their structure-function relationship, especially catalytic mechanism by using crystallography and high-resolution mass spectrometry (Parkkinen et al. (2011) J. Biol. Chem. 286, 27294). We have also good possibilities to study the catalyzed reactions by using molecular mechanics and quantum mechanics (ab initio) methods. This all should give novel and comprehensive atomic level view about some key steps in carbohydrate metabolism, which is useful when developing more efficient biocatalysts and microbial routes for biomass conversion to useful platform chemicals.