Isolation and characterization of a novel cyanophycin synthetase from a deep-sea sediment metagenomic library

Cyanophycin is non-ribosomally synthesized protein-like copolymer. Synthesis of cyanophycin is catalyzed by cyanophycin synthetase (CphA). In this study, a novel cyanophycin synthetase CphA49 belonging to NOR5 clade of Gammaproteobacteria was identified with primer-based screening from a deep-sea sediment metagenomic library. The cphA49 gene contained an open reading frame of 2,637 bp and encoded a protein with a predicted molecular mass of 100 kDa. A recombinant CphA49 was obtained by the functional expression of cphA49 in Escherichia coli BL21 (DE3). The biochemical properties of the purified CphA49 were determined. The optimum pH and temperature of the recombinant CphA49 were 9.0 and 40 °C, respectively. The enzyme was stable at temperatures below 40 °C. The recombinant CphA49 exhibited strict primer dependency and broad substrate specificities. Cyanophycin catalyzed by CphA49 exhibited homogenous molecular mass. The amino acid composition of cyanophycin was determined and constitutes arginine, aspartic acid, and lysine.