Overexpression and biochemical characterization of a recombinant psychrophilic endocellulase from Pseudoalteromonas sp. DY3

Cold-active cellulases have received great attention for both industrial applications and fundamental research because of their high activity at low temperatures and their unique structural characters. In this study, the cold-active endoglucanase CelX from psychrotrophic Pseudoalteromonas sp. DY3 was successfully overexpressed in E. coli, partly purified and characterized in detail. CelX showed the highest activity at pH 5.5, and exhibited moderate activity and superior pH stability over a wide pH range (pH 5.0-pH 9.0). It displayed the highest activity at 45 °C, and kept 34.7% residual activity even at 5 °C. It was stable below 35 °C and lost activity very quickly above 45 °C, which is consistent with its cold adaptability. The apparent kinetic parameters CelX against CMC (carboxymethyl cellulose) were determined, with the Km and kcat values of 6.4 mg/ml and 4.2 s−1 respectively. Mn2+ and Co2+ enhanced the cellulolytic activity of CelX by 28.8% and 20.6% respectively, whereas Pb2+ and Cu2+ inhibited its activity by 14.9% and 6.5% separately. The cold adaptation of CelX is possibly due to the presence of the unusually long linker between the catalytic module and the cellulose-binding domain.