Expression, purification and characterization of a thermostable lactate dehydrogenase from Thermotoga maritima

Abstract:

The gene encoding thermostable lactate dehydrogenase (Tm-LDH) was cloned into the plasmid pHsh from Thermotoga maritima, and expressed in Escherichia coli JM 109. The recombinant protein was purified to homogeneity by a simple step, heat treatment. The recombinant enzyme had a molecular mass of 33 kDa. The optimal temperature and pH of Tm-LDH were observed 95 ℃ and 7.0. The purified enzyme had a half-life of 2 h at 90 ℃, and exhibited better stability over a pH range from 5.5 to 8.0. The Km and Vmax values were 1.7 mmol/L, 3.8×104 U/mg of protein for pyruvate, and 7.2 mmol/L and 1.1×105 U/mg for NADH, respectively. The expression of Tm-LDH in T7 system could not obtain high efficiency, but it has been soluble over-expression in pHsh system and reached 340 mg/L. The superior stability and productivity of Tm-LDH will lay the foundation of its industrial-scale fermentation and application in the NAD regeneration.

Key words:thermostable lactate dehydrogenase, pHsh expression system, NAD regeneration