In Vitro Modification of Bacterial Cyanophycin and Cyanophycin Dipeptides Using Chemical Agents Towards Novel Variants of the Biopolymer

Abstract

Variations of the composition of cyanophycin (CGP) have been investigated since the early 2000s. Modifications of the polymer are of academical interest, but also expand the number of putative applications for CGP and its dipeptides in fields like food supplementations, and medical and cosmetic applications. Until recently variations of the composition occurred only in vivo. However, in the last years, two procedures using chemical or enzymatic in vitro modification were successfully applied. Since chemical treatments were more effective and reached higher conversion rates, a search for reagents and their applicability to conduct reactions with CGP was done. The reaction of CGP with methyl isocyanate resulted in the conversion of 50% of the lysine residues, while only 3% of the arginine residues were modified. However, using digested CGP dipeptides, the conversion rates of lysine increased slightly to 72%, while the conversion of arginine reached 96%. Using formaldehyde, CGP could be methylated with a conversion rate of 84% for lysine and 15% for arginine. Acetylation of lysine residues was obtained using acetic anhydride, reaching a conversion rate of 100% for a single acetylation, where 63% of the residues were acetylated twice. Arginine residues could be acetylated at a rate of 89%. Diacetyl could be added to 80% of all arginine residues, while lysine was not targeted by the compound. Other agents were also tested, but showed lesser or no conversion and/or inconclusive results. Overall, the tested reactions confirm the viability of chemical CGP modification for future approaches.

Cyanophycin Modifications—Widening the Application Potential

“…Cyanophycin can be included in the design of drugs and tissue engineering, as was recently demonstrated ( Tseng et al, 2018 ; Uddin et al, 2020 ). Chemical and enzymatic modifications of cyanophycin allow the introduction of new functional groups into the polymer, thus expanding the area of possible applications ( Wiefel et al, 2019a ).…”

“…Such polymer can be degraded by CphE, yielding new dipeptides like aspartate-homoarginine ( Frommeyer et al, 2014 ). Furthermore, it was proposed to introduce sulfur into lysine or arginine side chains, as it opens a path for further polymer modifications ( Wiefel et al, 2019a ). The reactions were conducted with methyl isocyanate and resulted in 50% conversion of lysine and 3% of arginine ( Figure 1I ).…”

“…However, the yield of the reaction was much higher with dipeptides as substrates (72 and 96% respectively). N-acetylarginine and N-acetyllysine residues were obtained on the side chain of cyanophycin when the polymer was treated with acetic anhydride ( Wiefel et al, 2019a ) ( Figure 1J ). Cyanophycin was treated with formaldehyde to obtain a methylated version of the polymer (yielding a conversion of 84% for lysine and 15% for arginine residues) ( Figure 1K ).…”

Recombinant Multi‐l‐Arginyl‐Poly‐l‐Aspartate (Cyanophycin) as an Emerging Biomaterial

“…[ 48 ] When methyl isocyanate, formaldehyde, acetic anhydride, and diacetyl react, respectively, with the primary amine and the guanidium groups at the terminal of MAPA side chains, the extent of modification can be controlled by the reaction conditions. [ 49 ]…”