Abstract

The ascomycete Geotrichum candidum is a versatile and efficient decay fungus that is involved, for example, in biodeterioration of compact discs; notably, the 3C strain was previously shown to degrade filter paper and cotton more efficiently than several industrial enzyme preparations. Glycoside hydrolase (GH) family 7 cellobiohydrolases (CBHs) are the primary constituents of industrial cellulase cocktails employed in biomass conversion, and feature tunnel-enclosed active sites that enable processive hydrolytic cleavage of cellulose chains. Understanding the structure-function relationships defining the activity and stability of GH7 CBHs is thus of keen interest. Accordingly, we report the comprehensive characterization of the GH7 CBH secreted by G. candidum (GcaCel7A). The bimodular cellulase consists of a family 1 cellulose-binding module (CBM) and linker connected to a GH7 catalytic domain that shares 64% sequence identity with the archetypal industrial GH7 CBH of Hypocrea jecorina (HjeCel7A). GcaCel7A shows activity on Avicel cellulose similar to HjeCel7A, with less product inhibition, but has a lower temperature optimum (50 degrees C versus 60-65 degrees C, respectively). Five crystal structures, with and without bound thio-oligosaccharides, show conformational diversity of tunnel-enclosing loops, including a form with partial tunnel collapse at subsite -4 not reported previously in GH7. Also, the first O-glycosylation site in a GH7 crystal structure is reported - on a loop where the glycan probably influences loop contacts across the active site and interactions with the cellulose surface. The GcaCel7A structures indicate higher loop flexibility than HjeCel7A, in accordance with sequence modifications. However, GcaCel7A retains small fluctuations in molecular simulations, suggesting high processivity and low endo-initiation probability, similar to HjeCel7A.

Keywords

biomass degradation; cellulase; Geotrichum candidum; molecular dynamics; X-ray structure

Published in

FEBS Journal
2015, Volume: 282, number: 23, pages: 4515-4537
Publisher: WILEY-BLACKWELL

SLU Authors

• Borisova, Anna

  • National Research Centre - Kurchatov Institute
  • The Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences
    

• Saleem, Umair

  • The Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences
    

• Sandgren, Mats

  • The Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences
    

• Payne, Christina M

  • The Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences
    

• Ståhlberg, Jerry

  • The Department of Chemistry and Biotechnology, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Biochemistry and Molecular Biology
Biocatalysis and Enzyme Technology
Structural Biology


Publication identifier

DOI: https://doi.org/10.1111/febs.13509

Permanent link to this page (URI)

https://res.slu.se/id/publ/73386