Page 31 - Advances in Textile Biotechnology

10 Advances in textile biotechnology

availability of proteases, amylases, laccases, phytases, and cellulases (Cherry
and Fidantsef, 2003).

1.4 Design and engineering of novel enzymes for
textile applications

Enzymes can be obtained from any live organism, but naturally occurring

enzymes are often not readily available in sufficient quantities for industrial
use. The advances of the last decade in genomics, proteomics and bioinfor-
matics created new opportunities to exploit an extremely large amount of
biological data that was not formerly available, and has allowed the exploi-
tation of such resources to create and develop innovative biotechnology-
based products. More than 50% of the industrially important enzymes are
engineered or produced from genetically engineered micro-organisms
(Hodgson, 1994).

1.4.1 Amylases

Amylases were the first and are still the most successful enzymes used in
textile industry for desizing to facilitate the removal of the starch-contain-
ing size that has served as a protective coating on yarns during weaving. In
order to reduce processing costs the desizing processing is sometimes com-
bined with the scouring and bleaching steps. In such instances, non-
enzymatic auxiliaries such as alkali or oxidation agents are typically used.
The desizing process is still the main application of amylases in textile
industry but their applications as additives in laundering detergent formu-
lations have increased recently.
The requirements for an optimal performance of amylases in both the
applications referred to above, mainly concern pH, oxidative stability, che-
lator resistance and temperature behaviors. So as to develop modifi ed amy-
lases with improved performance, various strategies are used, amongst
which protein engineering methods, such as random mutagenesis, homology
considerations and site-directed mutagenesis are widely used.
Declerck et al. (1990) and Joyet et al. (1992) increased the thermostabil-
ity of Bacillus licheniformis α-amylase (BLA) by two independent amino-
acid substitutions His133Tyr (or His133Ile) and Ala209Val (or Ala209Ile)
using random mutagenesis. This increase in enzyme thermostability is
presumably the result of entropy gain and better packing of the protein
structure.
Two regions that are important for the higher thermostability of BLA in
comparison to Bacillus amyloliquefaciens α-amylase (BAA) were fi rst iden-
tifed by Suzuki and collaborators (1989). Based on amino acid differences
observed in these two regions, three stabilizing mutations in the BAA

© Woodhead Publishing Limited, 2010