Fungal cellulases: Study of hydrolytic properties of endoglucanases from Trichoderma reesei and Humicola insolens

Research output: ThesisDoctoral Thesis (compilation)

Abstract

Cellulose is one of the most abundant biopolymers on earth. Several organisms degrade cellulose, one of the most studied is the fungus <i>Trichoderma reesei</i> which produces seven genetically different cellulases. In this thesis, a thorough study of the hydrolytic characteristics of the less studied endoglucanases Cel12A (EG III), Cel45A (EG V) and Cel61A (EG IV) of <i>T. reesei</i> is presented. Cel12A showed lower endoglucanase activity than the major endoglucanases Cel5A (EG II) and Cel7B (EG I), however, the endoglucanase activity for Cel12A was significantly higher than what was observed for Cel45A and Cel61A. The need for expressing Cel12A might be found in the low molecular mass, only 25 kDa compared to about 50 kDa for the major endoglucanases. A smaller enzyme might penetrate parts of a natural cellulosic substrate to which the major enzymes cannot access. Cel45A showed high activity against glucomannan and only a low endoglucanase activity. Thus, since no activity on mannan was observed for Cel45A, the hydrolytic properties indicates that this enzyme is a glucomannanase. For Cel61A, only a low endoglucanase activity was observed.

A novel approach to characterise soluble cellulose derivatives is presented. The cellulose derivative, carboxymethyl cellulose (CMC), was hydrolysed by a single endoglucanase and the products were analysed with several techniques, in particular liquid chromatography and MALDI-TOF mass spectrometry. Endoglucanases of the fungi <i>Humicola insolens</i> and <i>T. reesei</i> were used. Since the substituents inhibit the hydrolysis by the enzymes, total hydrolysis was not achieved by any endoglucanase. Furthermore, some of the endoglucanases were able to hydrolyse the CMC to higher extent than others. Thus, it is possible to use pure endoglucanases in analysing cellulose derivatives.

Cellulases are able to hydrolyse cellulose in co-operation, the enzymes act in synergy. When studying the hydrolysis of lignocellulose with the exoglucanase Cel7A (CBH I) in combination with the endoglucanase Cel5A several observations were made which did not fit the most accepted synergy model. Therefore, an extension to the endo-exo synergy model is presented. The concept is introduced that the observed synergy is due to removal of obstacles for the exoglucanase by the endoglucanase activity.

Details

Authors
  • Johan Karlsson
Organisations
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Biological Sciences

Keywords

  • Humicola insolens, Trichoderma reesei, endoglucanases, cellulose hydrolysis, carboxymethyl cellulose, synergy, Biochemistry, Biokemi, Metabolism, Chemical technology and engineering, Kemiteknik och kemisk teknologi
Original languageEnglish
QualificationDoctor
Awarding Institution
Supervisors/Assistant supervisor
  • [unknown], [unknown], Supervisor, External person
Award date2001 Jan 12
Publisher
  • Department of Biochemistry, Lund University
Print ISBNs91-7874-106-8
Publication statusPublished - 2000
Publication categoryResearch

Bibliographic note

Defence details Date: 2001-01-12 Time: 10:15 Place: Sal C, Kemicentrum, Sölvegatan 39, Lund External reviewer(s) Name: Claeyssens, Marc Title: Professor Affiliation: University of Gent, Gent, Belgium ---

Related research output

Johan Karlsson, Markku Saloheimo, Matti Siika-aho, Maija Tenkanen, Merja Penttilä & Folke Tjerneld, 2001, In: European Journal of Biochemistry. 268, 24, p. 6498-6507

Research output: Contribution to journalArticle

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