Structure and function of Humicola insolens family 6 cellulases: Structure of the endoglucanase, Cel6B, at 1.6 Å resolution

Gideon J. Davies*, A. Marek Brzozowski, Miroslawa Dauter, Annabelle Varrot, Martin Schülein

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Cellulases are traditionally classified as either endoglucanases or cellobiohydrolases on the basis of their respective catalytic activities on crystalline cellulose, which is generally hydrolysed more efficiently only by the cellobiohydrolases. On the basis of the Trichoderma reesei cellobiohydrolase II structure, it was proposed that the active-site tunnel of cellobiohydrolases permitted the processive hydrolysis of cellulose, whereas the corresponding endoglucanases would display open active-site clefts. Glycoside hydrolase family 6 contains both cellobiohydrolases and endoglucanases. The structure of the catalytic core of the family 6 endoglucanase Cel6B from Humicola insolens has been solved by molecular replacement with the known T. reesei cellobiohydrolase II as the search model. Strangely, at the sequence level, this enzyme exhibits the highest sequence similarity to family 6 cellobiohydrolases and displays just one of the loop deletions traditionally associated with endoglucanases in this family. However, this enzyme shows no activity on crystalline substrates but a high activity on soluble substrates, which is typical of an endoglucanase. The three dimensional structure reveals that the deletion of just a single loop of the active site, coupled with the resultant conformational change in a second 'cellobiohydrolase-specific' loop, peels open the active-site tunnel to reveal a substrate-binding groove.

Original languageEnglish
Pages (from-to)201-207
Number of pages7
JournalBiochemical journal
Issue number1
Publication statusPublished - 15 May 2000


  • Cellobiohydrolase
  • Cellulose
  • Glycoside hydrolase
  • X-ray structure

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