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.
Keywords: Escherichia coli; Extracellular secretion; OmpZ; pProEX-HTa-cgkZ; κ-Carrageenase.
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