Direct Delivery of Health Promoting β-Asp-Arg Dipeptides via Stable Co-expression of Cyanophycin and the Cyanophycinase CphE241 in Tobacco Plants

Meta-omic profiling reveals ubiquity of genes encoding for the nitrogen-rich biopolymer cyanophycin in activated sludge microbiomes

Recovering nitrogen (N) from municipal wastewater is a promising approach to prevent nutrient pollution, reduce energy use, and transition toward a circular N bioeconomy, but remains a technologically challenging endeavor. Existing N recovery techniques are optimized for high-strength, low-volume wastewater. Therefore, developing methods to concentrate dilute N from mainstream wastewater will bridge the gap between existing technologies and practical implementation. The N-rich biopolymer cyanophycin is a promising candidate for N bioconcentration due to its pH-tunable solubility characteristics and potential for high levels of accumulation. However, the cyanophycin synthesis pathway is poorly explored in engineered microbiomes. In this study, we analyzed over 3,700 publicly available metagenome assembled genomes (MAGs) and found that the cyanophycin synthesis gene cphA was ubiquitous across common activated sludge bacteria. We found that cphA was present in common phosphorus accumulating organisms (PAO) Ca. 'Accumulibacter' and Tetrasphaera, suggesting potential for simultaneous N and P bioconcentration in the same organisms. Using metatranscriptomic data, we confirmed the expression of cphA in lab-scale bioreactors enriched with PAO. Our findings suggest that cyanophycin synthesis is a ubiquitous metabolic activity in activated sludge microbiomes. The possibility of combined N and P bioconcentration could lower barriers to entry for N recovery, since P concentration by PAO is already a widespread biotechnology in municipal wastewater treatment. We anticipate this work to be a starting point for future evaluations of combined N and P bioaccumulation, with the ultimate goal of advancing widespread adoption of N recovery from municipal wastewater.

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

Multi-l-arginyl-poly-l-aspartate (MAPA) is a non-ribosomal polypeptide which synthesis is directed by cyanophycin synthetase, and its production can be achieved using recombinant microorganisms carrying the cphA gene. Along its poly-aspartate backbone, arginine or lysine links to each aspartate via an isopeptide bond. MAPA is a zwitterionic polyelectrolyte full of charged carboxylic, amine, and guanidino groups. In aqueous solution, MAPA exhibits dual thermal and pH responses similar to those stimuli-responsive polymers. Being biocompatible, the films containing MAPA can support cell proliferation and elicits minimal immune response in macrophages. Dipeptides from MAPA after enzymatic treatments can provide nutritional benefits. In light of the increasing interest in MAPA, this article focuses on the recent discovery of the function of cyanophycin synthetase and the potentials of MAPA as a biomaterial.

Cyanophycin and its biosynthesis: not hot but very cool

Covering: 1878 to early 2023Cyanophycin is a biopolymer consisting of a poly-aspartate backbone with arginines linked to each Asp sidechain through isopeptide bonds. Cyanophycin is made by cyanophycin synthetase 1 or 2 through ATP-dependent polymerization of Asp and Arg, or β-Asp-Arg, respectively. It is degraded into dipeptides by exo-cyanophycinases, and these dipeptides are hydrolyzed into free amino acids by general or dedicated isodipeptidase enzymes. When synthesized, chains of cyanophycin coalesce into large, inert, membrane-less granules. Although discovered in cyanobacteria, cyanophycin is made by species throughout the bacterial kingdom, and cyanophycin metabolism provides advantages for toxic bloom forming algae and some human pathogens. Some bacteria have developed dedicated schemes for cyanophycin accumulation and use, which include fine temporal and spatial regulation. Cyanophycin has also been heterologously produced in a variety of host organisms to a remarkable level, over 50% of the host's dry mass, and has potential for a variety of green industrial applications. In this review, we summarize the progression of cyanophycin research, with an emphasis on recent structural studies of enzymes in the cyanophycin biosynthetic pathway. These include several unexpected revelations that show cyanophycin synthetase to be a very cool, multi-functional macromolecular machine.

Phytochemical Characterization of Water Avens (Geum rivale L.) Extracts: Structure Assignment and Biological Activity of the Major Phenolic Constituents

Water avens (Geum rivale L.) is a common Rosaceae plant widely spread in Europe and North America. It is rich in biologically active natural products, some of which are promising as prospective pharmaceuticals. The extracts of water avens are well known for their triterpenoid metabolites and associated anti-inflammatory, antimicrobial and antioxidant activities. However, the polyphenolic profiles of G. rivale L. are still awaiting complete characterization. Accordingly, the contribution of its individual components to the antioxidant, antibacterial and neuroprotective activity of the extracts is still unknown. As this plant can be available on an industrial scale, a better knowledge of its properly-relevant constituents might give access to new highly-efficient pharmaceutical substances and functional products. Therefore, herein we comprehensively characterize the secondary metabolome of G. rivale by ESI-HR-MS, ESI-HR-MSⁿ and NMR spectroscopy with a special emphasis on the polyphenolic composition of its aerial parts. Furthermore, a multilateral evaluation of the antioxidant, neuroprotective and antibacterial properties of the aqueous and ethyl acetate fractions of the total aqueous alcoholic extract as well as individual isolated polyphenols was accomplished. Altogether four phenolic acid derivatives (trigalloyl hexose, caffeoyl-hexoside malate, ellagic acid and ellagic acid pentoside), six flavonoids (three quercetin derivatives, kaempferol and three its derivatives and two isorhamnetin derivatives) and four tannins (HHDP-hexoside, proantocyanidin dimer, pedunculagin I and galloyl-bis-HHDP-hexose) were identified in this plant for the first time. The obtained aqueous and ethyl acetate fractions of the total extract as well as the isolated individual compounds showed pronounced antioxidant activity. In addition, a pronounced antibacterial activity against several strains was proved for the studied fractions (for ethyl acetate fraction the highest activity against E. coli АТСС 25922 and S. aureus strains ATCC 27853 and SG-511 (MIC 15.6 μg/mL) was observed; for aqueous fraction-against Staphylococcus aureus SG-511 (MIC 31.2 μg/mL)). However, the anti-neurodegenerative (neuroprotective) properties could not be found with the employed methods. However, the antibacterial activity of the fractions could not be associated with any of the isolated individual major phenolics (excepting 3-O-methylellagic acid). Thus, the aerial parts of water avens represent a promising source of polyphenolic compounds with antioxidant activity and therefrom derived human health benefits, although the single constituents isolated so far lack a dominant selectively bioactive constituent in the bioassays performed.

The structure of cyanophycinase in complex with a cyanophycin degradation intermediate

BACKGROUND

Cyanophycinases are serine protease family enzymes which are required for the metabolism of cyanophycin, the natural polymer multi-L-arginyl-poly(L-aspartic acid). Cyanophycinases degrade cyanophycin to β-Asp-Arg dipeptides, which enables use of this important store of fixed nitrogen.

METHODS

We used genetic code expansion to incorporate diaminopropionic acid into cyanophycinase in place of the active site serine, and determined a high-resolution structure of the covalent acyl-enzyme intermediate resulting from attack of cyanophycinase on a short cyanophycin segment.

RESULTS

The structure indicates that cyanophycin dipeptide residues P1 and P1' bind shallow pockets adjacent to the catalytic residues. We observe many cyanophycinase - P1 dipeptide interactions in the co-complex structure. Calorimetry measurements show that at least two cyanophycin dipeptides are needed for high affinity binding to cyanophycinase. We also characterized a putative cyanophycinase which we found to be structurally very similar but that shows no activity and could not be activated by mutation of its active site.

GENERAL SIGNIFICANCE

Despite its peptidic structure, cyanophycin is resistant to degradation by peptidases and other proteases. Our results help show how cyanophycinase can specifically bind and degrade this important polymer.

Sustainable Production of the Cyanophycin Biopolymer in Tobacco in the Greenhouse and Field

The production of biodegradable polymers as coproducts of other commercially relevant plant components can be a sustainable strategy to decrease the carbon footprint and increase the commercial value of a plant. The biodegradable polymer cyanophycin granular polypeptide (CGP) was expressed in the leaves of a commercial tobacco variety, whose seeds can serve as a source for biofuel and feed. In T0 generation in the greenhouse, up to 11% of the leaf dry weight corresponded to the CGP. In T1 generation, the maximum content decreased to approximately 4% dw, both in the greenhouse and first field trial. In the field, a maximum harvest of 4 g CGP/plant could be obtained. Independent of the CGP content, most transgenic plants exhibited a slight yield penalty in the leaf biomass, especially under stress conditions in greenhouse and field trials. After the harvest, the leaves were either Sun dried or ensiled. The resulting material was used to evaluate the extraction of CGP compared to that in the laboratory protocol. The farm-level analysis indicates that the extraction of CGP from tobacco plants can provide alternative income opportunities for tobacco farmers. The CGP yield/ha indicates that the CGP production in plants can be economically feasible depending on the cultivation and extraction costs. Moreover, we analyzed the consumer acceptance of potential applications associated with GM tobacco in four European countries (Germany, Finland, Italy and the Netherlands) and found unexpectedly high acceptance.