期刊
BIOTECHNOLOGY FOR BIOFUELS
卷 4, 期 -, 页码 -出版社
BIOMED CENTRAL LTD
DOI: 10.1186/1754-6834-4-45
关键词
cellobiohydrolase 1; TrCeI7A; xylan; xylan oligosaccharide; binding; inhibition; biomass degradation; isothermal titration calorimetry
资金
- Danish Council for Strategic Research [09-063210, 2104-07-0028]
- US Department of Energy [DE-FC36-08GO18080]
Background: The well-studied cellulase mixture secreted by Trichoderma reesei (anamorph to Hypocrea jecorina) contains two cellobiohydolases (CBHs), cellobiohydrolase I (TrCeI7A) and cellobiohydrolase II (TrCel6A), that are core enzymes for the solubilisation of cellulose. This has attracted significant research interest because of the role of the CBHs in the conversion of biomass to fermentable sugars. However, the CHBs are notoriously slow and susceptible to inhibition, which presents a challenge for the commercial utilisation of biomass. The xylans and xylan fragments that are also present in the biomass have been suggested repeatedly as one cause of the reduced activity of CHBs. Yet, the extent and mechanisms of this inhibition remain poorly elucidated. Therefore, we studied xylan oligosaccharides (XOSs) of variable lengths with respect to their binding and inhibition of both TrCeI7A and an enzyme variant without the cellulose-binding domain (CBM). Results: We studied the binding of XOSs to TrCeI7A by isothermal titration calorimetry. We found that XOSs bind to TrCeI7A and that the affinity increases commensurate with XOS length. The CBM, on the other hand, did not affect the affinity significantly, which suggests that XOSs may bind to the active site. Activity assays of TrCeI7A clearly demonstrated the negative effect of the presence of XOSs on the turnover number. Conclusions: On the basis of these binding data and a comparison of XOS inhibition of the activity of the two enzyme variants towards, respectively, soluble and insoluble substrates, we propose a competitive mechanism for XOS inhibition of TrCeI7A with phosphoric swollen cellulose as a substrate.
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