Biomedical Engineering Reference
In-Depth Information
for the beverage industry (Edens et al. 2005) and cellulases for bio-based
applications (Visser et al. 2011). Next to these, the genome sequences of a
few dozen other fi lamentous fungi have been determined and are being
explored for interesting enzymes like the discovery of many lignocellulose
degrading enzymes in white rot fungi (Martinez et al. 2004).
Although nature is thus offering a wide range of fungal enzymes
with interesting different kinetic properties, these may not always be
at the effi ciency which is needed for an economic compatible industrial
process. In order to improve the catalytic properties protein engineering
and directed evolution are employed. Genencor made use of a modifi ed
T. reesei
host to create the proper screening conditions in order to select
for improved cellulases (Lantz et al. 2010). Alternatively, the screening
process can be done
in silico,
facilitated by homology modelling. Roche
applied this method on fungal phytases leading to several degrees increase
in thermostability (Lehmann et al. 2002). Further developments will come
with the ever increasing knowledge and the next generation of enzymes
might even come from
de novo
design, as recently been applied for Kemp
eliminases (Khersonsky et al. 2011).
INDUSTRIAL PRODUCTION
Some isolates of fungal strains as
A. niger
and
T. reesei
produce high
concentrations of extracellular enzymes. Over the years these benefi ts were
further exploited via directed additional modifi cations (such as reducing
native protease activity; Dunn-Coleman et al. 1991) and classical strain
improvement (leading to amplifi cation of the glucoamylase gene cluster;
van Dijck et al. 2003) facilitated by robotic screening into highly effi cient
production systems. Recently, Dyadic developed
C. lucknowense
in to a
production host via extensive selection for strains with low viscous growth
(Burlingame 2003) competing with the systems used by Novozymes,
Genencor, Amano, DSM and others.
This highly competitive fi eld has stimulated each company to develop
and try to patent their own specifi c production system. Some examples
include:
(1) expression of heterologous products such as bovine chymosin as
fusion protein with
A. niger
glucoamylase (Genencor; Cullen et al.
1987).
(2)
engineered protein glycosylation sites (Chr. Hansen; van den Brink
et al. 2006).
(3)
deleting elements of the Unfolded Protein Response (UPR) leads to
higher levels of heterologous products (DSM; Jacobs et al. 2010)
