Biochemical characteristics and function of a threonine dehydrogenase encoded byste11in Ebosin biosynthesis ofStreptomycessp. 139

Abstract

Aims: Ebosin, a novel exopolysaccharide (EPS) produced by Streptomyces sp. 139 has antagonistic activity for interleukin‐1 receptor (IL‐1R) in vitro and remarkable anti‐rheumatic arthritis activity in vivo. Ebosin biosynthesis gene (ste) cluster has been identified in our laboratory. This paper reports our effort to characterize the function of ste11 gene. Methods and Results: After the ste11 gene was cloned and expressed in Escherichia coli BL21, the recombinant Ste11 was purified and found capable of catalyzing NAD+ and l‐threonine to NADH and 2‐amino‐3‐ketobutyrate, hence identified as a threonine dehydrogenase (TDH). To investigate its function in the biosynthesis of Ebosin, the ste11 gene was knocked out with a double crossover via homologous recombination. The monosaccharide composition of EPS produced by the mutant strain (EPS‐m) was altered from that of Ebosin. The analysis of IL‐1R antagonist activity for EPSs showed that the bioactivity of EPS‐m was lower than Ebosin. Conclusions: ste11 gene encoding a TDH may function as a modifier gene of Ebosin during its biosynthesis. Significance and Impact of the Study: TDH encoded by ste11 is functional in Ebosin biosynthesis. It is the first characterized TDH in Streptomyces.