Riin Kont will defend her doctoral thesis titled "The acquisition of cellulose chain by a processive cellobiohydrolase" on Wednesday, 20 September 2017 at 12.15 at Estonian Biocentre (Riia 23b-105).
Dr.Priit Väljamäe, Institute of Molecular and Cell Biology, University of Tartu
Associate Professor Kiyohiko Igarashi, PhD, University of Tokyo (Japan)
Description of the problem
Deposits of carbon in plant biomass has a huge potential to contribute to the worldwide chemical and biofuel production. The major component of plant cell walls is cellulose. In cellulose, glucose residues are joined into long chains, which, in turn, have a regular arrangement and form a crystalline lattice in plant cell walls. For industrial use, it is often essential to degrade polysaccarides into its soluble monomeric compounds. The main biomass degraders in nature are microorganisms who secrete a myriad of different enzymes for deconstruction of biomass. The enzymes secreted to deconstruct cellulose are cellulases. The key enzymes for cellulose deconstruction use processive hydrolytic mechanism. Once associated with cellulose chain, these enzymes perform several consecutive catalytic acts before dissociation. The industrially relevant producers of cellulases are the cellulase hyper-producing strains of soft rot fungus Trichoderma reesei. The key cellulase of T.reesei is a processive cellulase TrCel7A.
Result and benefit
The primary targets of this research were the molecular mechanisms of the processive catalytic cycle of TrCel7A. In particular, the author focused on the role of aromatic amino acid Trp38 at the entrance region of the active site of TrCel7A in processive catalytic cycle. Trp38 was found to be an important determinant for feeding the cellulose chain into the active site of the enzyme. Additionally, its absence increases the dissotiation of the enzyme from the substrate and, thereby, decreases the processivity. Regarding the acquisition of cellulose chain by TrCel7A, it was also found that the binding of glucose residues in the subsite +2 in the active site was anomer-selective. It is proposed that this anomer-specific interaction with the substrate contributes to the processivity of TrCel7A. The main findings of this research increase our understanding of the deconstruction mechanisms of cellulose and thereby contribute to the development of new technologies of biorefinement.