Page 34 - Advances in Textile Biotechnology

Design and engineering of novel enzymes for textile applications 13

1.4.2 Pectinases
Pectinolytic enzymes or pectinases are a complex group of enzymes involved
in the degradation of pectic substances. They are primarily produced in
nature by saprophytes and plant pathogens (bacteria and fungi) for degra-
dation of plant cell walls (Lang and Dörenberg, 2000). There are three
major classes of pectin-degrading enzymes: pectin esterases (PEs), polyga-
lacturonases (PGs) and polygalacturonate lyases (PGLs), and their poten-
tial for bioscouring have been exploited (Choe et al., 2004; Ibrahim et al.,
2004; Karapinar and Sariisik, 2004; Li and Hardin, 1997; Tzanov et al., 2001).
Despite all the research done to develop an efficient bioscouring process,

there is still no broad commercial application on the industrial scale. There
is thus still a demand for a pectinase with higher activity and stability at
high temperatures and alkaline conditions. Solbak and collaborators devel-
oped a novel pectate lyase using directed evolution that has improved
thermostability. The new enzyme contains eight point mutations (Ala-
118His, Tyr190Leu, Ala197Gly, Ser208Lys, Ser263Lys, Asn275Tyr, Tyr309Trp,
and Ser312Val). Compared to the wild-type enzyme, it presented a 16 °C
higher melting temperature and exhibited improved bioscouring perform-
ance at low enzyme dosage in a high-temperature bioscouring process
(Solbak et al., 2005).

1.4.3 Cellulases

Cellulases are hydrolytic enzymes that catalyse the breakdown of cellulose

to smaller oligosaccharides and finally glucose. Cellulase activity refers to
a multicomponent enzyme system combining at least three types of cellu-
lases, endoglucanases or endocellulases, cellobiohydrolases or exo-
cellulases and β-4-glucosidase working synergistically together (Teeri,
1997). These enzymes are commonly produced by soil-dwelling fungi and
bacteria, the most important being Trichoderma, Penicillium and Fusarium
(Jorgensen et al., 2005; Kuhad et al., 1999; Verma et al., 2007). Cellulases
from bacteria and fungi were first introduced in textile industry for denim

finishing and are now also successfully used in laundry detergents. The yield

of bacterial cellulases is normally low (Knowles et al., 1987) making fungal
cellulases more promising and suitable for industrial applications. However,
fungal cellulases have optimum activities at acidic pH. Their activities are
greatly reduced at pH > 6, thus limiting the application of fungal cellulases
under neutral or alkaline conditions. Therefore, protein engineering of cel-
lulases has predominantly been used as a tool to increase the catalytic
efficiency of these enzymes at higher pH. Becker et al., (2001) reported a

variant of T. reesei Cel7A containing five point mutations (Glu223Ser/
Ala224His/Leu225Val/Thr226Ala/Asp262Gly) and having a more alkaline

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