Characterization of the catalytic domains of Trichoderma reesei endoglucanase I, II, and III, expressed in Escherichia coli

The genes encoding the catalytic domains (CD) of the three endoglucanases (EG I; Cel7B, EG II; Cel5A, and EG III; Cel12A) from Trichoderma reesei QM9414 were expressed in Escherichia coli strains Rosetta-gami B (DE3) pLacI or Origami B (DE3) pLacI and were found to produce functional intracellular proteins. Protein production by the three endoglucanase transformants was evaluated as a function of growth temperature. Maximal productivity of EG I-CD at 15°C, EG II-CD at 20°C and EG III at 37°C resulted in yields of 6.9, 72, and 50 mg/l, respectively. The endoglucanases were purified using a simple purification method based on removing E. coli proteins by isoelectric point precipitation. Specific activity toward carboxymethyl cellulose was found to be 65, 49, and 15 U/mg for EG I-CD, EG II-CD, and EG III, respectively. EG II-CD was able to cleave 1,3-1,4-β-d-glucan and soluble cellulose derivatives. EG III was found to be active against cellulose, 1,3-1,4-β-d-glucan and xyloglucan, while EG I-CD was active against cellulose, 1,3-1,4-β-d-glucan, xyloglucan, xylan, and mannan.