Characterization of a novel arabinose-tolerant α-L-arabinofuranosidase with high ginsenoside Rc to ginsenoside Rd bioconversion productivity

Abstract

Aims: (i) To investigate the enzymatic characterization of α-L-arabinofuranosidase from Thermotoga thermarum DSM5069. (ii) To evaluate the performance of its excellent properties on converting ginsenoside Rc to ginsenoside Rd. Methods and Results: The thermostable α-L-arabinofuranosidase (Tt-Afs) gene from T. thermarum DSM5069 was cloned and overexpressed. Recombinant Tt-Afs was purified, and its molecular weight was approx. 55 kDa. Its optimal activity was at pH 5·0 and 95°C. It has high selectivity for cleaving the outer arabinofuranosyl moieties at the C-20 carbon of ginsenoside Rc and its sugar-tolerance makes Tt-Afs a promising candidate for the production of ginsenoside Rd. In a reaction at 85°C and pH 5·0, 25 g l-1 of ginsenoside Rc was transformed into 21·8 g l-1 of Rd within 60 min, with a corresponding molar conversion of 99·4% and a high ginsenoside Rd productivity of 21800 mg l-1 h-1. Conclusions: We have successfully cloned and overexpressed the novel α-L-arabinofuranosidase from T. thermarum DSM5069. The high ginsenoside Rd productivity and detailed characterization of recombinant Tt-Afs was provided. Significance and Impact of the Study: The result shows a high productivity on the bioconversion from high concentration ginsenoside Rc to ginsenoside Rd, which also give rise to a potential commercial enzyme application.