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. 2009 Sep 1:2:19.
doi: 10.1186/1754-6834-2-19.

Metabolic engineering strategies for the improvement of cellulase production by Hypocrea jecorina

Christian P Kubicek  1 , Marianna Mikus, André Schuster, Monika Schmoll, Bernhard Seiboth
Affiliations

Metabolic engineering strategies for the improvement of cellulase production by Hypocrea jecorina

Christian P Kubicek et al. Biotechnol Biofuels. .

Abstract

Hypocrea jecorina (= Trichoderma reesei) is the main industrial source of cellulases and hemicellulases used to depolymerise plant biomass to simple sugars that are converted to chemical intermediates and biofuels, such as ethanol. Cellulases are formed adaptively, and several positive (XYR1, ACE2, HAP2/3/5) and negative (ACE1, CRE1) components involved in this regulation are now known. In addition, its complete genome sequence has been recently published, thus making the organism susceptible to targeted improvement by metabolic engineering. In this review, we summarise current knowledge about how cellulase biosynthesis is regulated, and outline recent approaches and suitable strategies for facilitating the targeted improvement of cellulase production by genetic engineering.

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Figures

Figure 1
Figure 1
Lactose and D-galactose catabolism in Hypocrea jecorina. The heterodisaccharide lactose is cleaved extracellularly into its monomers D-glucose and D-galactose. While D-glucose is assimilated via glycolysis (not shown), D-galactose can be converted by two different pathways. The galactokinase of the classical Leloir pathway (left) is specific for α-D-galactose and therefore, β-D-galactose has to be epimerised to the α-anomer before it can enter this pathway. A second pathway identified in Hypocrea jecorina starts with the reduction of both anomeric forms of D-galactose to galactitol. Two hypothetical pathways are drafted for the further degradation of galactitol.
Figure 2
Figure 2
Schematic model of the proposed function of GNA3. Upon activation by its cognate G-protein coupled receptor (GPCR), GNA3 causes increased cAMP-levels and acts on its downstream effector. These events result in positive modulation of cellulase gene transcription, the induction of which is initiated by an as yet unidentified pathway. Transcription of gna3 is enhanced by light, negatively regulated by ENVOY and activation of GNA3 is decreased by a regulator of the G-protein signalling protein. The GNA3 downstream pathway leading to modulation of cellulase gene transcription is perturbed in darkness.
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References

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