Features of the biotechnologically relevant polyamide family cyanophycins'' and their biosynthesis in prokaryotes and eukaryotes

Cyanophycin, inclusions in cyanobacteria discovered by the Italian scientist Borzi in 1887, were characterized as a polyamide consisting of aspartic acid and arginine. Its synthesis in cyanobacteria was analyzed regarding growth conditions, responsible gene product, requirements, polymer structure and properties. Heterologous expression of diverse cyanophycin synthetases (CphA) in Escherichia coli enabled further enzyme characterization. Cyanophycin is a polyamide with variable composition and physiochemical properties dependent on host and cultivation conditions in contrast to the extracellular polyamides poly--glutamic acid and poly-epsilon-l-lysine. Furthermore, recombinant prokaryotes and transgenic eukaryotes, including plants expressing different cphA genes, were characterized as suitable for production of insoluble cyanophycin regarding higher yields and modified composition for other requirements and applications. In addition, cyanophycin was characterized as a source for the synthesis of polyaspartic acid or N-containing bulk chemicals and dipeptides upon chemical treatment or degradation by cyanophycinases, respectively. Moreover, water-soluble cyanophycin derivatives with altered amino acid composition were isolated from transgenic plants, yeasts and recombinant bacteria. Thereby, the range of dipeptides could be extended by biological processes and by chemical modification, thus increasing the range of applications for cyanophycin and its dipeptides, including agriculture, food supplementations, medical and cosmetic purposes, synthesis of the polyacrylate substitute poly(aspartic acid) and other applications.