TY - JOUR

T1 - Activity of fungal β-glucosidases on cellulose

AU - Keller, Malene B.

AU - Sørensen, Trine H.

AU - Krogh, Kristian B.R.M.

AU - Wogulis, Mark

AU - Borch, Kim

AU - Westh, Peter

PY - 2020

Y1 - 2020

N2 - Background: 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. Results: We studied the activity of four fungal GH3 BGs on cellulose and found significant activity. At low temperatures (10 °C), we derived the approximate kinetic parameters k cat = 0.3 ± 0.1 s-1 and K M = 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. Conclusions: Overall 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.

AB - Background: 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. Results: We studied the activity of four fungal GH3 BGs on cellulose and found significant activity. At low temperatures (10 °C), we derived the approximate kinetic parameters k cat = 0.3 ± 0.1 s-1 and K M = 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. Conclusions: Overall 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.

KW - Beta-glucosidases (BG)

KW - Cellulose

KW - Enzyme specificity

KW - Glucoside Hydrolase Family 3 (GH3)

U2 - 10.1186/s13068-020-01762-4

DO - 10.1186/s13068-020-01762-4

M3 - Journal article

C2 - 32670408

AN - SCOPUS:85087978023

VL - 13

JO - Biotechnology for Biofuels

JF - Biotechnology for Biofuels

SN - 1754-6834

IS - 1

M1 - 121

ER -