MOLECULAR CHARACTERIZATION OF CYANOPHYCIN SYNTHETASE, THE ENZYME CATALYZING THE BIOSYNTHESIS OF THE CYANOBACTERIAL RESERVE MATERIAL MULTI-L-ARGINYL-POLY-L-ASPARTATE (CYANOPHYCIN)

Cyanophycin (multi-L-arginyl-poly-L-aspartate), a water-insoluble rese rve polymer of cyanobacteria, is a product of nonribosomal peptide syn thesis. The purification of cyanophycin synthetase of the cyanobacteri um Anabaena variabilis is described. In sodium dodecylsulfate/polyacry lamide gel electrophoresis, the enzyme preparation shows one band with an apparent molecular mass of 100 kDa. The native enzyme has an appar ent molecular mass of approximately 230 kDa, as determined by size-exc lusion chromatography, suggesting that the active form is a homodimer. During catalysis, ATP is converted to ADP, The gene coding for cyanop hycin synthetase has been identified in the sequenced genome of Synech ocystis sp. PCC 6803. The C-terminal 60% of the deduced amino acid seq uence of cyanophycin synthetase show sequence similarity to enzymes of the superfamily of ligases involved in the biosynthesis of murein and of folyl-poly(gamma-glutamate). Cells of Escherichia coli harbouring the gene on a plasmid express active synthetase and accumulate cyanoph ycin-like material. The results prove that a single enzyme catalyzes t he de novo synthesis of cyanophycin.