Improving the production of recombinant L-Asparaginase-II in Escherichia coli by co-expressing catabolite repressor activator ( cra ) gene

Identification of a single genetic target for microbial strain improvement is difficult due to the complexity of the genetic regulatory network. Hence, a more practical approach is to identify bottlenecks in the regulatory networks that control critical metabolic pathways. The present work focuses on enhancing cellular physiology by increasing the metabolic flux through the central carbon metabolic pathway. Global regulator cra (catabolite repressor activator), a DNA-binding transcriptional dual regulator was selected for the study as it controls the expression of a large number of operons that modulate central carbon metabolism. To upregulate the activity of central carbon metabolism, the cra gene was co-expressed using a plasmid-based system. Co-expression of cra led to a 17% increase in the production of model recombinant protein L-Asparaginase-II. A pulse addition of 0.36% of glycerol every two hours post-induction, further increased the production of L-Asparaginase-II by 35% as compared to the control strain expressing only recombinant protein. This work exemplifies that upregulating the activity of central carbon metabolism by tuning the expression of regulatory genes like cra can relieve the host from cellular stress and thereby promote the growth as well as expression of recombinant hosts.