1. Structural polysaccharides – cellulose and chitin – are the most abundant polysaccharides on the Earth and represent a huge reservoir of renewable carbon. Their enzymes aided valorization provides green and sustainable alternative to traditional petroleum-based industry. However, the crystalline structure of cellulose and chitin makes them recalcitrant towards enzymatic degradation. Development of optimal enzyme mixtures assumes in depth understanding of the mode of action and kinetics of individual enzyme components. Hence, detailed analysis of enzyme kinetics and mechanism is on the main focus of our research group.
2. Enzymatic degradation of recalcitrant polysaccharides (cellulose and chitin)
Owing to their crystalline structure, the enzymatic degradation of cellulose and chitin takes place on the solid liquid interface. This is a complex heterogeneous catalysis that involves number of intermediate steps. Identification of the rate limiting step (bottleneck) is prerequisite for accelerating the whole reaction. The key approach of our research is the development of novel methods that enable to measure the rates of individual intermediate steps of complex catalysis. In this way we have measured processivity and the values of rate constants of dissociation, association and glycosidic bond hydrolysis by glycoside hydrolases. Besides traditional glycoside hydrolases we are also focused on lytic polysaccharide monooxygenases (LPMOs). LPMOs are recently discovered redox enzymes that catalyze oxidative degradation of recalcitrant polysaccharides. Understanding the mechanism and kinetics of LPMO catalysis may help better harnessing of their catalytic potential and increase the efficiency of degradation and modification of recalcitrant polysaccharides.
Redox reactions in lignocellulose degradation
LPMO catalysis needs electrons (reductant) as well as H2O2/O2 co-substrate (oxidant). Recognition of the importance of LPMOs has also boosted the research of the redox reactions that contribute to degradation of lignocellulose (the main component of plant cell walls). Here we focus on the development of enzyme cascades that enable to establish optimal conditions for LPMO activity and stability in the complex redox active environment. Besides LPMOs we are interested in different enzymes like laccases, peroxidases and oxidases that are active on lignin or its degradation products.
Scheme used in the header: A complex reaction of LPMO-mediated cellulose degradation, where everything does not depend on the enzyme alone (author: Priit Väljamäe).