Surface Modification of Cellulose Acetate with Cutinase and ...

Surface Modification of Cellulose Acetate with Cutinase and Cutinase Fused to Carbohydrate-binding Modules
7). The fusion of cutinase to the CBMs had a more pronounced effect for the less
substituted acetate, independently of the CBM type. The steric constrains should be
stronger in the triacetate fibre and consequently the interactions necessary for the ligand
recognition by the CBM should be more impaired on this fibre surface regarding the
diacetate fibre. Due to the fact that different initial amounts of protein were used, is not
possible to compare directly the protein adsorption behaviour of the several constructs.
But it is possible to see for this particular treatment that there was no obvious relation
between the colour differences and the amount of protein adsorbed.
Taking in account the different esterase activities used, the cutinase-wtCBMCBHI and
cutinase-sCBMCBHI seem the most efficient catalysts under the treatment conditions
used. For CDA, the relative K/S was improved 3.8 and 2.6 fold by cutinase-wtCBMCBHI
and cutinase-sCBMCBHI, respectively, regarding cutinase alone. For treated CTA, the
relative increase in K/S was not different between cutinase alone and fused to the fungal
CBMs, but the initial esterase activity of cutinase was higher (figure. 7). The differences
in relative K/S were also improved with the fusion of the bacterial CBM to cutinase. For
CDA, cutinase-CBMN1 improved the relative K/S by 1.8 fold, the same as cutinase-
PTboxCBMN1.
The treatment was performed at pH 8. The optimum pH for binding of most CBMs
corresponds to the optimum pH for the catalytic domain of the respective carbohydrate-
active enzyme and it is in the range of acidic to neutral. The better performance on
cellulose acetate fibres of the fungal CBM could be explained by the affinity of
CBMCBHI to insoluble ligands being relatively more insensitive to pH than the affinity
of CBMN1 (Tomme et al., 1996). In fact, lowering the treatment pH to neutral increased
the adsorption of cutinase-CBMN1 to CDA (results not shown). Other reason could be
the difference in size of both CBMs. The activity of cutinase could be more constrained
by the bigger bacterial CBM than by the smaller fungal CBM. Indeed, using half the
esterase activity in the treatment with cutinase-PTboxCBMN1, the increase in K/S
obtained was in the same range of that with cutinase-CBMN1, for both fabrics (figure.
7).
Further studies, aiming at a better characterization of the action of chimeric cutinases on
the surface modification of cellulose acetates, would contribute to clarify these issues.
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