Role of a family 11 carbohydrate-binding module in the function of a recombinant cellulase used to supplement a barley-based diet for broiler chickens

Abstract

1. Cellulases and xylanases display a modular architecture that comprises a catalytic module linked to one or more non-catalytic carbohydrate-binding modules (CBMs). CBMs have been classified into 52 different families, based on primary structure similarity. These non-catalytic modules mediate a prolonged and intimate contact of the enzyme with the target substrate eliciting efficient hydrolysis of the target polysaccharides.

2. A study was undertaken to investigate the importance of a family 11 CBM, displaying high affinities for barley β-glucans, in the function of recombinant derivatives of cellulase CtLic26A-Cel5E of Clostridium thermocellum used to supplement a barley-based diet for broiler chicken.

3. The results showed that birds fed on diets containing the recombinant CtLic26A-Cel5E modular derivatives or the commercial enzyme mixture Rovabio™ Excel AP displayed improved performance when compared with birds fed on diets not supplemented with exogenous enzymes.

4. It is suggested that the enzyme dosage used in this study (30 U/kg of basal diet), was probably too high for the efficacy of the family 11 CBM to be noticed. It remains to be established if the targeting effect resulting from the incorporation of CBMs in plant cell wall hydrolases may be effective at lower exogenous enzyme dosages.

Acknowledgements

We thank Sociedade Agrícola da Quinta da Freiria SA for supplying the chicks and Reagro for providing the feed ingredients used in these experiments. This work was supported by Fundação para a Ciência e a Tecnologia (POCI/CVT/69329/2006). CG, TR and PP were supported by Fundação para a Ciência e a Tecnologia through grants SFRH/BD/16731/2004, SFRH/BD/32321/2006 and SFRH/BD/17969/2004, respectively.