Enzymatic properties of the low molecular mass endoglucanases Cel12A (EG III) and Cel45A (EG V) of Trichoderma reesei

Abstract

Trichoderma reesei produces five known endoglucanases. The most studied are Cel7B (EG I) and Cel5A (EG II) which are the most abundant of the endoglucanases. We have performed a characterisation of the enzymatic properties of the less well-studied endoglucanases Cel12A (EG III), Cel45A (EG V) and the catalytic core of Cel45A. For comparison, Cel5A and Cel7B were included in the study. Adsorption studies on microcrystalline cellulose (Avicel) and phosphoric acid swollen cellulose (PASC) showed that Cel5A, Cel7B, Cel45A and Cel45Acore adsorbed to these substrates. In contrast, Cel12A adsorbed weakly to both Avicel and PASC. The products formed on Avicel, PASC and carboxymethylcellulose (CMC) were analysed. Cel7B produced glucose and cellobiose from all substrates. Cel5A and Cel12A also produced cellotriose, in addition to glucose and cellobiose, on the substrates. Cel45A showed a clearly different product pattern by having cellotetraose as the main product, with practically no glucose and cellobiose formation. The kinetic constants were determined on cellotriose, cellotetraose and cellopentaose for the enzymes. Cel12A did not hydrolyse cellotriose. The k Cat values for Cel12A on cellotetraose and cellopentaose were significantly lower compared with Cel5A and Cel7B. Cel7B was the only endoglucanase which rapidly hydrolysed cellotriose. Cel45Acore did not show activity on any of the three studied cello-oligosaccharides. The four endoglucanases’ capacity to hydrolyse β-glucan and glucomannan were studied. Cel12A hydrolysed β-glucan and glucomannan slightly less compared with Cel5A and Cel7B. Cel45A was able to hydrolyse glucomannan significantly more compared with β-glucan. The capability of Cel45A to hydrolyse glucomannan was higher than that observed for Cel12A, Cel5A and Cel7B. The results indicate that Cel45A is a glucomannanase rather than a strict endoglucanase.