Xylan oligosaccharides and cellobiohydrolase I (TrCeI7A) interaction and effect on activity

Martin Johannes Baumann, Kim Borch, Peter Westh

Research output: Contribution to journalJournal articlepeer-review

Abstract

Background
The well-studied cellulase mixture secreted by Trichoderma reesei (anamorph to Hypocrea jecorina) contains two cellobiohydolases (CBHs), cellobiohydrolase I (TrCel7A) and cellobiohydrolase II (TrCeI6A), 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 TrCel7A and an enzyme variant without the cellulose-binding domain (CBM).

Results
We studied the binding of XOSs to TrCel7A by isothermal titration calorimetry. We found that XOSs bind to TrCel7A 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 TrCel7A 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 TrCel7A with phosphoric swollen cellulose as a substrate.
Original languageEnglish
JournalBiotechnology for Biofuels
Volume4
Issue number45
ISSN1754-6834
DOIs
Publication statusPublished - 2011

Keywords

  • cellobiohydrolase 1
  • TrCel7A
  • xylan
  • xylan oligosaccharide
  • binding
  • inhibition
  • biomass degradation
  • isothermal titration calorimetry

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