Biomedical Engineering Reference
In-Depth Information
CONCLUSION
The production of plant cell wall degrading enzymes by fungi is a complex
process that is dependent on getting the correct extracellular signal (most
probably a soluble disaccharide of glucose) that sets in motion a cascade of
transcription factors. The transcription factor story is further complicated
as it is also affected by other physiological parameters, including,
starvation, pH and temperature. There is also feedback inhibition as the
end product of action of the enzymes (Glucose/Xylose) represses enzyme
expression. A complete understanding of this process would not only be
benefi cial to commercial enzyme producers but would also enhance the
use of fungi as a host organism for heterologous expression of proteins.
Cellulase production on an industrial scale requires the use of an
inexpensive soluble inducing substrate. Currently lactose is the inducing
substrate of choice for the fungus T. reesei ; however, this disaccharide found
in milk does not drive cellulose expression nearly as well as the exorbitantly
expensive sophorose. Elucidation of the precise mechanism of cellulose
induction would identify the enzyme responsible for the production of
sophorose (or other inducing carbohydrates) and ultimately allow the
large-scale production of this product.
The quantity of cellulase enzyme produced during induction and the
level of control of expression make the promoters of these genes ideal
candidates for use in over-expression of heterologous proteins. A complete
understanding of the transcription factors involved in the induction/
repression of cellulases will allow more widespread use of the fungi as
heterologous hosts.
References
Aro, N., M. Ilmen, A. Saloheimo and M. Penttila. 2003. ACEI of Trichoderma reesei
is a repressor of cellulase and xylanase expression. Appl. Environ. Microbiol .
69: 56-65.
Aro, N., T. Pakula and M. Penttila. 2005. Transcriptional regulation of plant cell
wall degradation by fi lamentous fungi. FEMS. Microbiol. Rev . 29: 719-739.
Aro, N., A. Saloheimo, M. Ilmen and M. Penttila. 2001. ACEII, a novel
transcriptional activator involved in regulation of cellulase and xylanase
genes of Trichoderma reesei . J. Biol. Chem . 276: 24309-24314.
Arst, H.N., Jr., D. Tollervey, C.E. Dowzer and J.M. Kelly. 1990. An inversion
truncating the creA gene of Aspergillus nidulans results in carbon catabolite
derepression. Mol. Microbiol . 4: 851-854.
Bisaria, V.S. and S. Mishra. 1989. Regulatory aspects of cellulase biosynthesis and
secretion. CRC Crit. Rev. Biotechnol . 9: 61-103.
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