Lignocellulosic waste contain a huge amount of polymers (cellulose and hemicellulose) that can be used for obtaining added-value products, as ethanol, food additives, or several compounds to be used for different biotechnological applications. During the last years, our research group has been involved in the characterization of fungal enzymes acting on different components of lignocellulosic biomass; hence they can also be used for valorisation of this kind of residues.
The sterol esterase produced by Ophiostoma piceae displays wide substrate specificity, hydrolyzing both tryglicerides and sterol esters, similarly to some enzymes from the Candida rugosa-like family. This enzyme also catalyzes esterification and transesterification reactions in mono- and byphasic organic systems. When compared to commercial sterol esterases or lipases, including those from C. rugosa, the enzyme showed to have better catalytic properties against all substrates assayed. Its potential application in the paper pulp industry (removal of unwanted lipidic deposits) and food industry (synthesis of phytosterol/stanol esters as additives for dairy products to reduce cholesterol levels) has been suggested. The native and recombinant proteins are both available, being the last one more soluble and efficient in hydrolysis reactions. The crystal structure of the recombinant esterase has been recently elucidated, revealing that the active form of the protein is dimeric, and confirming the presence of an internal tunnel, whose shape and dimensions may explain the increased effectiveness of this enzyme.
On the other hand, we have also characterized three beta-glucosidases and one beta-xylosidase from a fungal isolate from cereal residues, recently identified as Talaromyces amestolkiae. After obtaining their nucleotidic sequence, and on the basis of sequence homology with other proteins included in databases, some of these enzymes have been modelled. In general, commercial cocktails are deficient in beta-glucosidases and beta-xylosidases. Then, these enzymes are of paramount importance in the field of 2G ethanol production, since their use increase saccharification yields as they are involved in the last step of cellulose and hemicellulose hydrolysis to fermentable monosaccharides. In addition, and depending on the reaction conditions, they also catalyze transglycosilation reactions, synthesizing novel compounds of interest for several biotechnological areas.
The main objectives of the current proposal are getting a deeper understanding on the properties and activity of these enzymes, and developing applications related to valorization of lignocellulosic waste The specific tasks are: a) expression in heterologous hosts to improve sterol esterase activity and to obtain recombinant beta-glycosidases; b) characterization of the recombinant proteins; c) rational design for enhancing activity/selectivity; d) immobilization of selected catalysts; e) in silico search of novel enzymes; f) development of applications intended for valorization of lignocellulosic waste. A number of EPOs have demonstrated their interest in the follow-up and potential results’ transfer of this proposal, either providing waste of their industrial activity as raw material for our research (LA CIBELES and NATAC), or collaborating in specific tasks (BIOPOLIS).