Purification, activity assays and crystallization of GtCel45A - a small cellulase enzyme from the brown-rot fungus Gloeophyllum trabeum expressed in Aspergillus nidulans

Abstract: Cellulose is the most abundant polymer on earth. It is one of the main components in lignocellulosic biomass, which has great potential as a renewable energy source. To utilize the biomass, for instance in biofuel production, cellulose needs to be degraded. In nature there are microorganisms that are specialized on such degradation, and they produce interesting cellulose hydrolysing enzymes. Understanding the function of these enzymes can hence be one step towards a more sustainable future.  The aim of this project was to find out if the enzyme GtCel45A from Gloeophyllum trabeum could hydrolyse soluble oligosaccharides and produce mono- or disaccharides as products. The study was executed by cultivating Aspergillus nidulans A773 recombinantly expressing GtCel45A followed by a purification process consisting of anion exchange chromatography and size exclusion chromatography. From 1.4 liters of culture, grown for 8 days at 30°C, 9.9 mg of purified GtCel45A was obtained. Activity measurements using p-hydroxybenzoic acid hydrazide (PHBAH) reagent for reducing sugar showed that the enzyme is active against and does hydrolyse barley beta-glucan. However, no hydrolysis of cellohexaose, cellotetraose, cellotriose or cellobiose could be detected, even after 223 minutes of incubation with GtCel45A as shown by carbohydrate analysis with high performance anion exchange chromatography with pulsed amperiometric detection (HPAE-PAD). In addition, a number of crystallization trials were performed, which resulted in formation of crystals that could subsequently be used to solve the structure of the protein.