EFFECT OF HYDRATION ON THE THERMAL STABILITY OF ENZYME

The thermal stability of New Zealand culture rabbit muscle aldolase was investigated by differential scanning calorimetry in the water content range 0.23-3.70 g water per g protein.The experimental results showed that at water contents below 0.47g/g,an endothermic peak was observed and at water contents above 0.57g/g,an endothermic and an exothermic peak were both observed on DSC thermogram.Thermal denaturation result of the enzyme and the relationship between two transition temperatures and water contents were first reported in this paper.Up to now we have not seen any similar reports concerning the exothermic transition.

Surface display of carbonic anhydrase on Escherichia coli for CO_(2) capture and mineralization

Mineralization catalyzed by carbonic anhydrase(CA)is one of the most promising technologies for capturing CO_(2).In this work,Escherichia coli BL21(DE3)was used as the host,and the N-terminus of ice nucleation protein(INPN)was used as the carrier protein.Different fusion patterns and vectors were used to construct CA surface display systems forα-carbonic anhydrase(HPCA)from Helicobacter pylori 26695 andα-carbonic anhydrase(SazCA)from Sulfurihydrogenibium azorense.The surface display system in which HPCA was fused with INPN via a flexible linker and intermediate repeat sequences showed higher whole-cell enzyme activity,while the enzyme activity of the SazCA expression system was significantly higher than that of the HPCA expression system.The pET22b vector with the signal peptide PelB was more suitable for the cell surface display of SazCA.Cell frac-tionation and western-blot analysis indicated that SazCA and INPN were successfully anchored on the cell’s outer membrane as a fusion protein.The enzyme activity of the surface display strain E-22b-I RL S(11.43 U⋅mL^(−1) OD 600−1)was significantly higher than that of the intracellular expression strain E-22b-S(8.355 U⋅mL^(−1) OD 600−1)under optimized induction conditions.Compared with free SazCA,E-22b-I RL S had higher thermal and pH stability.The long-term stability of SazCA was also significantly improved by surface display.When the engineered strain and free enzyme were used for CO_(2) mineralization,the amount of CaCO_(3) deposition catalyzed by the strain E-22b-I RL S on the surface(241 mg)was similar to that of the free SazCA and was significantly higher than the intracellular expression strain E-22b-S(173 mg).These results demonstrate that the SazCA surface display strain can serve as a whole-cell biocatalyst for CO_(2) capture and mineralization.