Identification and characterization of a novel spermidine/spermine acetyltransferase encoded by gene ste26 from Streptomyces sp. 139

Streptomyces sp. 139 produces a novel exopolysaccharide (EPS) designated Ebosin which can bind IL-1R specifically and exhibits anti-rheumatic arthritis activity in vivo. With the Ebosin biosynthesis gene cluster (ste) consisting of 27 ORFs identified previously the focus of this study was to characterize the protein encoded by ste26 gene. After cloning and expressing ste26 in Escherichia coli BL21, we purified the recombinant Ste26 protein and revealed its ability of transferring the acetyl group from AcCoA to spermidine and spermine, with spermine being the preferred substrate. Therefore Ste26 has been determined to be a spermidine/spermine acetyltransferase which can use spermine (Km of 72.1 ± 7.4 μM), spermidine (Km of 147.2 ± 11 μM), AcCoA (Km of 45.7 ± 2.5 μM) and poly-l-lysine (Km of 99.7 ± 11 μM) as substrates. The optimum pH, temperature and time for the activity have been shown to be 7.5, 37°C and 10 min, respectively. This is the first spermidine/spermine acetyltransferase characterized in Streptomyces and its function in Ebosin biosynthesis is discussed.