Abstract
BackgroundFungal beta-glucosidases (BGs) from glucoside hydrolase family 3 (GH3) are industrially important enzymes, which convert cellooligosaccharides into glucose; the end product of the cellulolytic process. They are highly active against the β-1,4 glycosidic bond in soluble substrates but typically reported to be inactive against insoluble cellulose.ResultsWe studied the activity of four fungal GH3 BGs on cellulose and found significant activity. At low temperatures (10 ℃), we derived the approximate kinetic parameters kcat = 0.3 ± 0.1 s−1 and KM = 80 ± 30 g/l for a BG from Aspergillus fumigatus (AfBG) acting on Avicel. Interestingly, this maximal turnover is higher than reported values for typical cellobiohydrolases (CBH) at this temperature and comparable to those of endoglucanases (EG). The specificity constant of AfGB on Avicel was only moderately lowered compared to values for EGs and CBHs.ConclusionsOverall these observations suggest a significant promiscuous side activity of the investigated GH3 BGs on insoluble cellulose. This challenges the traditional definition of a BG and supports suggestions that functional classes of cellulolytic enzymes may represent a continuum of overlapping modes of action.
Highlights
Fungal beta-glucosidases (BGs) from glucoside hydrolase family 3 (GH3) are industrially important enzymes, which convert cellooligosaccharides into glucose; the end product of the cellulolytic process
Aspergillus nidulans BG, Magnaporthe grisea BG, Penicillium oxalicum BG, and Aspergillus fumigatus BG were tested for activity against microcrystalline cellulose (Avicel)
A phylogenetic tree of sequences annotated as GH3 enzymes were retrieved from the carbohydrate-active enzymes (CAZy) database
Summary
Fungal beta-glucosidases (BGs) from glucoside hydrolase family 3 (GH3) are industrially important enzymes, which convert cellooligosaccharides into glucose; the end product of the cellulolytic process They are highly active against the β-1,4 glycosidic bond in soluble substrates but typically reported to be inactive against insoluble cellulose. The classical definition of these three categories is that cellobiohydrolases (CBHs) attack an end (reducing or non-reducing) of a cellulose strand on the Keller et al Biotechnol Biofuels (2020) 13:121 and EG This mode of action is sometimes called endoprocessive, and while this may represent a minor reaction path for Cel7A from T. reesei, other cellulases seem to use endo-processive activity as their primary mechanism [6, 7]. These observations again point towards an endo-processive mechanism, where the EG, in contrast to the notion of random attacks, breaks the strand internally and subsequently makes a few additional cuts adjacent to the initial hydrolysis point
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
