The major component of the plant cell wall – cellulose – and the major component of the crustaceans’ exoskeleton – chitin – are the two most abundant polysaccharides in nature. They provide a huge reserve of organic carbon, making use of which would provide a green alternative for oil based fuels and commodity products. Industrial scale usage of cellulose and chitin is hampered by their crystalline structure, which makes them recalcitrant towards both chemical and enzymatic breakdown. Processive cellulases and chitinases are the key enzymes in degradation of recalcitrant polysaccharides. They are also primary targets in protein engineering for improved performance. The main research focus of our group is the enzyme kinetics of processive glucoside hydrolases. We want to know, which step is the rate limiting one for the whole reaction. For that reason we have developed methods to assess the rate of different steps of the hydrolysis cycle: (i) binding to the substrate, (ii) complexation of the enzyme and the polymer chain of the substrate, (iii) processive hydrolysis of the substrate, and (iv) dissociation. We also look for the correlations between rates of different steps of the hydrolysis cycle and the structures of both, the substrate and the enzyme.
As a practical output for these fundamental studies we participate together with different partners from other countries in the process of developing the industrial production of second generation bioethanol. We participate in developing industrially more efficient cellulases and chitinases. Our role here is to describe enzymatic properties of the mutant cellulases and chitinases made by our partners.
Role of enzymes processivity in degradation of recalcitrant polysaccharides
This project is a part of Norwegian-Estonian Research Cooperation Programme and is financed by the Norwegian Financal Mechanism 2009-2014. The project focuses on in-depth studies of processive enzymes involved in cellulose and chitin degradation. We combine the large catalogue of chitinases and cellulases available at Dr. Sørlie’s lab at Norwegian University of Life Sciences with the substrate-labeling technologies and other research methods, which we have developed. This will generate new fundamental insights into processivity, one of the most important properties of the enzymes used in chitin and cellulose biorefining.
Rational engineering of cellulases for improved saccharification of biomass
This is a cooperation project with Dr. Peter Westh from the University of Roskilde, Denmark. The objective of this project is to develop different cellulase variants that are optimized for the conditions of industrial scale second generation bioethanol production.
Inhibitors of cellulases
Second generation bioethanol production from lignocellulosic biomass can be divided into three steps: pretreatment, saccharification and fermentation. One of the most promising methods for lignocellulose pretreatment is the hydrothermal pretreatment. However, it can result in formation of the compounds that are inhibitory for the enzymes involved in the biomass saccharification step and also for the microorganisms in the fermentation phase. We have isolated strong cellulase inhibitors from the hydrothermally pretreated wheat straw. Inhibitors were oligosaccharides and composed of the mixture of gluco- and xylooligosaccharides. Now we are trying to purify different components of the mixture to homogeneity and also to solve the crystal structure of the enzyme-inhibitor complex.
Priit Väljamäe, docent, Ph. D., priit.valjamae [ät] ut.ee, +3727375823
Silja Kuusk, research scientist, Ph. D., silja.kuusk [ät] ut.ee, +3727375823
Jürgen Jalak, lecturer, M. Sc., jyrgen.jalak [ät] ut.ee
Riin Kont, research scientist, Ph. D, riin.kont [ät] ut.ee
Ragnar, undergraduate student