Efficient extracellular production of κ-carrageenase in Escherichia coli: effects of wild-type signal sequence and process conditions on extracellular secretion.

Signal peptides direct proteins to translocate across the bacterial cytoplasmic membrane. This study aimed to improve the level of extracellular secretion of recombinant carrageenase by recombining the gene encoding wild-type signal peptide (OmpZ) of Zobellia sp. ZM-2 κ-carrageenase into the expression vector pProEX-HTa-cgkZ. The recombinant strain BL21-HTa-cgkZ achieved extracellular secretion of κ-carrageenase. The effects of induction, culture conditions, and additives were investigated to further promote the extracellular secretion of the enzyme. Results showed that the wild-type signal sequence secreted recombinant κ-carrageenase out of the cytoplasmic membrane. Low temperature (23 °C) and optimum isopropyl-β-thiogalactoside concentration (0.9 mM) favored soluble protein expression. Moreover, additives such as lactose, glycine, Tween-80, and TritonX-100 promoted the release of intracellular enzymes. The existence of OmpZ resulted in 51% of the total κ-carrageenase accumulation secreted into culture medium, and 33% accumulated in the periplasmic space. High extracellular secretion of recombinant κ-carrageenase under the optimum conditions showed promising applications of the process for extracellular protein production.