Incorporation of alternative amino acids into cyanophycin by different cyanophycin synthetases heterologously expressed in Corynebacterium glutamicum

Cyanophycin (multi-l-arginyl-poly-l-aspartic acid; also known as cyanophycin grana peptide [CGP]) is a biopolymer that could be used in various fields, for example, as a potential precursor for the synthesis of polyaspartic acid or for the production of CGP-derived dipeptides. To extend the applications of this polymer, it is therefore of interest to synthesize CGP with different compositions. A recent re-evaluation of the CGP synthesis in C. glutamicum has shown that C. glutamicum is a potentially interesting microorganism for CGP synthesis with a high content of alternative amino acids. This study shows that the amount of alternative amino acids can be increased by using mutants of C. glutamicum with altered amino acid biosynthesis. With the DM1729 mutant, the lysine content in the polymer could be increased up to 33.5 mol%. Furthermore, an ornithine content of up to 12.6 mol% was achieved with ORN2(P-gdh4). How much water-soluble or insoluble CGP is synthesized is strongly related to the used cyanophycin synthetase. CphA(Dh) synthesizes soluble CGP exclusively. However, soluble CGP could also be isolated from cells expressing CphA(6308)Delta 1 or CphA(6308)Delta 1_C595S in addition to insoluble CGP in all examined strains. The point mutation in CphA(6308)Delta 1_C595S partially resulted in a higher lysine content. In addition, the CGP content could be increased to 36% of the cell dry weight under optimizing growth conditions in C. glutamicum ATCC13032. All known alternative major amino acids for CGP synthesis (lysine, ornithine, citrulline, and glutamic acid) could be incorporated into CGP in C. glutamicum.

Automated summary

By using mutants and optimizing growth conditions, cyanophycin with different compositions, including high content of alternative amino acids, can be synthesized in C. glutamicum. The solubility or insolubility of synthesized CGP is strongly influenced by the cyanophycin synthetase used. The study demonstrates that C. glutamicum is capable of incorporating major alternative amino acids such as lysine, ornithine, citrulline, and glutamic acid into CGP.