Effective degradation of curdlan powder by a novel endo-β-1→3-glucanase

Curdlan is a water-insoluble microbial exo-polysaccharide that is hardly degraded. The gene CcGluE encoding an endo-β-1→3-glucanase consisting of 412 amino acids (44 kDa) from Cellulosimicrobium cellulans E4-5 was cloned and expressed in Escherichia coli. The recombinant CcGluE hydrolysed curdlan powder effectively. CcGluE shows high endo-β-1→3 glucanase activity and low β-1,4 and β-1,6 glucanase activities with broad substrate specificity for glucan, including curdlan, laminarin and β-1→3/1→6-glucan, and the highest catalytic activity for curdlan. Moreover, the hydrolytic products of curdlan were glucan oligosaccharides with degrees of polymerisation of 2-13, and the main products were glucobiose and glucotriose. Degradation mode analysis indicated that CcGluE is more likely to hydrolyse glucopentaose and revealed that CcGluE was an endo-glucanase. Furthermore, upon combination with a homogenising pre-treatment method with curdlan, the degradation efficiency of CcGluE for curdlan powder was greatly improved 7.1-fold, which laid a good foundation for the utilisation of curdlan.