High-level extracellular expression of κ-carrageenase in Brevibacillus choshinensis for the production of a series of κ-carrageenan oligosaccharides

In this study, the gene of the catalytic domain of the kappa-carrageenase from Pseudoalteromonas porphyrae LL1 (PpCGKCD) was efficiently expressed in Brevibacillus choshinensis. Under the optimized conditions, the highest activity of the extracellular kappa-carrageenase reached to 51.5 +/- 1.2 U/mL with 96 h. Subsequently, the catalytic domain of the kappa-carrageenase (PpCgkCD) was purified and detected by SDS-PAGE, indicating that the PpCgkCD had a molecular weight of 32 kDa. The optimal pH and temperature of the PpCgkCD were 8.0 and 40 degrees C, respectively. Notably, the PpCgkCD showed considerable stability below 35 degrees C and over a relatively broad range of alkaline pHs, even at pH of 11.0 for 12 h. Besides, 100.0 mM of Mg2+ could dramatically enhance the activity of the PpCgkCD by 97.5%. TLC and ESI-Q-TOF MS/MS analysis revealed that the enzymatic hydrolysates were composed of An-G4S-type neocarrabiose units, and the end-products were neo-kappa-carrabiose and neo-kappa-carratetraose. Furthermore, the PpCgkCD could be employed to efficiently hydrolyze kappa-carrageenan via a random non-processive mechanism for the production of a series of even-numbered x-carrageenan oligosaccharides. This study demonstrated that the PpCgkCD secreted by B. choshinensis had great potential in the commercial production of bioactive oligosaccharide from kappa-carrageenan.