Cloning，Expression and Immobilization of Glutamine Synthetase from Corynebacterium glutamicum

Abstract:

The glutamine synthetase encoded gene of Corynebacterium glutamicum was cloned and mutated on polyadenylation sites，followed by heterogeneous expression in E. coli with high enzyme activity of 6.215 U/mg. The recombinant mutant enzyme（GS'） was purified，and LX1000-EP resin was employed as the immobilization carrier. The results showed that the optimal conditions for immobilization were in the following：0.176 g carriers/1 U enzyme，pH 8.0，25 ℃ and 16 h. Under the above conditions the highest bioactivity （3.658 U/g） of immobilized GS' was achieved with high active recovery rate of 67.17%. Compared with free enzyme，the immobilized GS has the same optimal temperature and stability，however the optimal pH was slightly increased. The immobilized GS has the same conversion rate of 92.83% when 50 mmol/L glutamate was added in the bioconversion system. This work is useful for further large-scale bioproduction of glutamine.