title: Competitive inhibition of cellobiohydrolase I by manno-oligosaccharides.
abstract: In the hydrolysis of softwood, significant amounts of manno-oligosaccharides (MOS) are released from mannan, the major hemicelluloses in softwood. However, the impact of MOS on the performance of cellulases is not yet clear. In this work, the effect of mannan and MOS in cellulose hydrolysis by cellulases, especially cellobiohydrolase I (CBHI) from Thermoascus aurantiacus (Ta Cel7A), was studied. The glucose yield of Avicel decreased with an increasing amount of added mannan. Commercial cellulases contained mannan hydrolysing enzymes, and β-glucosidase played an important role in mannan hydrolysis. Addition of 10mg/ml mannan reduced the glucose yield of Avicel (at 20g/l) from 40.1 to 24.3%. No inhibition of β-glucosidase by mannan was observed. The negative effects of mannan and MOS on the hydrolytic action of cellulases indicated that the inhibitory effect was at least partly attributed to the inhibition of Ta Cel7A (CBHI), but not on β-glucosidase. Kinetic experiments showed that MOS were competitive inhibitors of the CBHI from T. aurantiacus, and mannobiose had a stronger inhibitory effect on CBHI than mannotriose or mannotetraose. For efficient hydrolysis of softwood, it was necessary to add supplementary enzymes to hydrolyze both mannan and MOS to less inhibitory product, mannose.
authors.affiliation: College of Forestry, Northwest A&F University, 3 Taicheng Road, Yangling 712100, China.
authors.forename: Donglin
authors.initials: D
authors.lastname: Xin
authors.affiliation: College of Forestry, Northwest A&F University, 3 Taicheng Road, Yangling 712100, China.
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Ge
authors.affiliation: College of Forestry, Northwest A&F University, 3 Taicheng Road, Yangling 712100, China.
authors.forename: Zongping
authors.initials: Z
authors.lastname: Sun
authors.affiliation: Department of Food and Environmental Sciences, University of Helsinki, P.O. Box 27, FIN 00014 Helsinki, Finland.
authors.forename: Liisa
authors.initials: L
authors.lastname: Viikari
authors.affiliation: College of Forestry, Northwest A&F University, 3 Taicheng Road, Yangling 712100, China. Electronic address: junhuazhang@nwsuaf.edu.cn.
authors.forename: Junhua
authors.initials: J
authors.lastname: Zhang
mesh_terms: D001426:Bacterial Proteins / Q000037:antagonists & inhibitors*; D001667:Binding, Competitive; D002480:Cellulase / Q000378:metabolism; D002482:Cellulose / Q000378:metabolism; D043366:Cellulose 1,4-beta-Cellobiosidase / Q000037:antagonists & inhibitors*; D006868:Hydrolysis; D008351:Mannans / Q000494:pharmacology*; D009844:Oligosaccharides / Q000494:pharmacology*; D013329:Structure-Activity Relationship; D055327:Thermoascus / Q000201:enzymology*; D014312:Trisaccharides / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D008351:Mannans; D009844:Oligosaccharides; D014312:Trisaccharides; C014647:mannobiose; C039922:mannotetraose; C023872:mannotriose; D002482:Cellulose; D002480:Cellulase; D043366:Cellulose 1,4-beta-Cellobiosidase
keywords: Cellobiohydrolase; Enzymatic hydrolysis; Inhibition; Mannan; Manno-oligosaccharides