Wound Healing Attributes of Polyelectrolyte Multilayers Prepared with Multi‐ l ‐arginyl‐poly‐ l ‐aspartate Pairing with Hyaluronic Acid and γ‐Polyglutamic Acid

Cyanophycin modifications for applications in tissue scaffolding

Cyanophycin (CGP) is a polypeptide consisting of amino acids-aspartic acid in the backbone and arginine in the side chain. Owing to its resemblance to cell adhesive motifs in the body, it can be considered suitable for use in biomedical applications as a novel component to facilitate cell attachment and tissue regeneration. Although it has vast potential applications, starting with nutrition, through drug delivery and tissue engineering to the production of value-added chemicals and biomaterials, CGP has not been brought to the industry yet. To develop scaffolds using CGP powder produced by bacteria, its properties (e.g., biocompatibility, morphology, biodegradability, and mechanical strength) should be tailored in terms of the requirements of the targeted tissue. Crosslinking commonly stands for a primary modification method for renovating biomaterial features to these extents. Herein, we aimed to crosslink CGP for the first time and present a comparative study of different methods of CGP crosslinking including chemical, physical, and enzymatic methods by utilizing glutaraldehyde (GTA), UV exposure, genipin, 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride/N-hydroxysuccinimide (EDC/NHS), and monoamine oxidase (MAO). Crosslinking efficacy varied among the samples crosslinked via the different crosslinking methods. All crosslinked CGP were non-cytotoxic to L929 cells, except for the groups with higher GTA concentrations. We conclude that CGP is a promising candidate for scaffolding purposes to be used as part of a composite with other biomaterials to maintain the integrity of scaffolds. The initiative study demonstrated the unknown characteristics of crosslinked CGP, even though its feasibility for biomedical applications should be confirmed by further examinations. KEY POINTS: • Cyanophycin was crosslinked by 5 different methods • Crosslinked cyanophycin is non-cytotoxic to L929 cells • Crosslinked cyanophycin is a promising new material for scaffolding purposes.

An Insight into Biodegradable Polymers and their Biomedical Applications for Wound Healing

Biodegradable polymers, encompassing both natural and synthetic polymers, have demonstrated efficacy as carriers for synthetic drugs, natural bioactive molecules, and inorganic metals. This is due to their ability to control the release of these substances. As a result, various advanced materials, such as nanoparticle- loaded hydrogels, nanofibrous scaffolds, and nanocomposites, have been developed. These materials have shown promise in enhancing processes, such as cell proliferation, vascular angiogenesis, hair growth, and wound healing management. Natural polymers, including hyaluronic acid, collagen, chitosan, gelatin, and alginate, as well as synthetic polymers like polylactic acid, polyglycolic acid, polylactic co-glycolic acid, and PCA, have significant potential for promoting wound healing. This study examines the advancements in biodegradable polymers for wound healing, specifically focusing on each polymer and its distinctive formulations. It also discusses the in vitro experiments conducted using different cell lines, as well as the in vivo studies that explore the numerous uses of these polymers in wound healing. The discussion also included the exploration of modifications or combinations of several polymers, as well as surface changes, in order to produce synergistic effects and address the limitations of individual polymers. The goal was to expedite the healing process of different chronic wounds. Due to this, there have been notable advancements in the technological use of polymeric mixes, including biodegradable polymer-based scaffolds, which have accelerated the process of wound healing.

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.

Recent Progress on Hyaluronan-Based Products for Wound Healing Applications

Hyaluronic acid (HA) based nanocomposites are considered excellent for improving wound healing. HA is biocompatible, biodegradable, non-toxic, biologically active, has hemostatic ability, and resists bacterial adhesion. HA-based nanocomposites promote wound healing in four different sequential phases hemostasis, inflammation, proliferation, and maturation. The unique biological characteristics of HA enable it to serve as a drug, an antibacterial agent, and a growth factor, which combine to accelerate the healing process. In this review, we focus on the use of HA-based nanocomposites for wound healing applications and we describe the importance of HA for the wound healing process in each sequential phase, such as hemostasis, inflammation, proliferation, and maturation. Metal nanoparticles (MNPs) or metal oxide nanoparticles (MO-NPs) loaded with HA nanocomposite are used for wound healing applications. Insights into important antibacterial mechanisms are described in HA nanocomposites. Furthermore, we explain antibiotics loaded with HA nanocomposite and its combination with the MNPs/MO-NPs used for wound healing applications. In addition, HA derivatives are discussed and used in combination with the other polymers of the composite for the wound healing process, as is the role of the polymer in wound healing applications. Finally, HA-based nanocomposites used for clinical trials in animal models are presented for wound healing applications.

A cryptic third active site in cyanophycin synthetase creates primers for polymerization

Cyanophycin is a nitrogen reserve biopolymer in many bacteria that has promising industrial applications. Made by cyanophycin synthetase 1 (CphA1), it has a poly-L-Asp backbone with L-Arg residues attached to each aspartate sidechain. CphA1s are thought to typically require existing segments of cyanophycin to act as primers for cyanophycin polymerization. In this study, we show that most CphA1s will not require exogenous primers and discover the surprising cause of primer independence: CphA1 can make minute quantities of cyanophycin without primer, and an unexpected, cryptic metallopeptidase-like active site in the N-terminal domain of many CphA1s digests these into primers, solving the problem of primer availability. We present co-complex cryo-EM structures, make mutations that transition CphA1s between primer dependence and independence, and demonstrate that primer dependence can be a limiting factor for cyanophycin production in heterologous hosts. In CphA1, domains with opposite catalytic activities combine into a remarkable, self-sufficient, biosynthetic nanomachine.

Structure and Function of the β-Asp-Arg Polymerase Cyanophycin Synthetase 2

Cyanophycin is a biopolymer composed of long chains of β-Asp-Arg. It is widespread in nature, being synthesized by many clades of bacteria, which use it as a cellular reservoir of nitrogen, carbon, and energy. Two enzymes are known to produce cyanophycin: cyanophycin synthetase 1 (CphA1), which builds cyanophycin from the amino acids Asp and Arg by alternating between two separate reactions for backbone extension and side chain modification, and cyanophycin synthetase 2 (CphA2), which polymerizes β-Asp-Arg dipeptides. CphA2 is evolutionarily related to CphA1, but questions about CphA2's altered structure and function remain unresolved. Cyanophycin and related molecules have drawn interest as green biopolymers. Because it only has a single active site, CphA2 could be more useful than CphA1 for biotechnological applications seeking to produce modified cyanophycin. In this study, we report biochemical assays on nine cyanobacterial CphA2 enzymes and report the crystal structure of CphA2 from Gloeothece citriformis at 3.0 Å resolution. The structure reveals a homodimeric, three-domain architecture. One domain harbors the polymerization active site and the two other domains have structural roles. The structure and biochemical assays explain how CphA2 binds and polymerizes β-Asp-Arg and highlights differences in in vitro oligomerization and activity between CphA2 enzymes. Using the structure and distinct activity profile as a guide, we introduced a single point mutation that converted Gloeothece citriformis CphA2 from a primer-dependent enzyme into a primer-independent enzyme.

Cyanophycin Modifications-Widening the Application Potential

A circular bioeconomy approach is essential to slowing down the fearsome ongoing climate change. Replacing polymers derived from fossil fuels with biodegradable biobased polymers is one crucial part of this strategy. Cyanophycin is a polymer consisting of amino acids produced by cyanobacteria with many potential applications. It consists mainly of aspartic acid and arginine, however, its composition may be changed at the production stage depending on the conditions of the polymerization reaction, as well as the characteristics of the enzyme cyanophycin synthetase, which is the key enzyme of catalysis. Cyanophycin synthetases from many sources were expressed heterologously in bacteria, yeast and plants aiming at high yields of the polymer or at introducing different amino acids into the structure. Furthermore, cyanophycin can be modified at the post-production level by chemical and enzymatic methods. In addition, cyanophycin can be combined with other compounds to yield hybrid materials. Although cyanophycin is an attractive polymer for industry, its usage as a sole material remains so far limited. Finding new variants of cyanophycin may bring this polymer closer to real-world applications. This short review summarizes all modifications of cyanophycin and its variants that have been reported within the literature until now, additionally addressing their potential applications.

Glucose-responsive hydrogel enhances the preventive effect of insulin and liraglutide on diabetic nephropathy of rats

Diabetic nephropathy (DN) is one of the most serious complications of diabetes mellitus. The combination of insulin (Ins) with liraglutide (Lir) has a greater potential for preventing DN than monotherapy. However, the renal protective effect of the combined Ins/Lir therapy is largely compromised due to their short half-lives after subcutaneous injection. Herein, a glucose-responsive hydrogel was designed in situ forming the dynamic boronic esters bonds between phenylboronic acid-grafted γ-Polyglutamic acid (PBA-PGA) and konjac glucomannan (KGM). It was hypothesized that the KGM/PBA-PGA hydrogel as the delivery vehicle of Ins/Lir would enhance the combinational effect of the latter on preventing the DN progress. Scan electronic microscopy and rheological studies showed that KGM/PBA-PGA hydrogel displayed good glucose-responsive property. Besides, the glucose-sensitive release profile of either Ins or Lir from KGM/PBA-PGA hydrogel was uniformly displayed at hyperglycemic level. Furthermore, the preventive efficacy of KGM/PBA-PGA hydrogel incorporating insulin and liraglutide (Ins/Lir-H) on DN progress was evaluated on streptozotocin-induced rats with diabetic mellitus (DM). At 6 weeks after subcutaneous injection of Ins/Lir-H, not only the morphology of kidneys was obviously recovered as shown by ultrasonography, but also the renal hemodynamics was significantly improved. Meanwhile, the 24-h urinary protein and albumin/creatinine ratio were well modulated. Inflammation and fibrosis were also largely inhibited. Besides, the glomerular NPHS-2 was obviously elevated after treatment with Ins/Lir-H. The therapeutic mechanism of Ins/Lir-H was highly associated with the alleviation of oxidative stress and activation of autophagy. Conclusively, the better preventive effect of the combined Ins/Lir via KGM/PBA-PGA hydrogel on DN progress was demonstrated as compared with their mixed solution, suggesting KGM/PBA-PGA hydrogel might be a potential vehicle of Ins/Lir to combat the progression of DN.

Improved Exopolymer Production by Chromohalobacter canadensis Cultures for Its Potential Cosmeceutical Applications

Several exopolymers with different chemical composition and correspondingly variety in their physico-chemical properties from halophilic microorganisms have still been described, however, with a low production yield. Chromohalobacter canadensis 28 isolated from Pomorie saltern synthesized an unusual exopolymer (EP) containing 72% γ-polyglutamic acid (PGA), an essential cosmeceutical additive. Current work suggests a novel approach for effective EP synthesis by C. canadensis 28 using continuous cultures. Highest production was observed at low dilution rates reaching a level of 2.1 mg/mL at D = 0.035, similar to those in batch cultures (2.34 mg/mL), however avoiding all disadvantages of discontinuous fermentation processes. At steady state, the total quantities of the synthesized EP after 48 h cultivation for the given equipment volume in D = 0.035 h⁻¹ and D = 0.075 h⁻¹ were 8.67 and 12 g, correspondingly, while it was 2.9 g for batch culture. Process parameters did not change after a ten-day run at D = 0.35 h⁻¹. A degree of purity of EP fraction received from continuous cultures was significantly increased up to 93–96%. A lack of cytotoxicity and high cell viability were observed for human dermal fibroblast cells after 24 h incubation with crude EP from C. canadensis 28 and purified PGA fraction that could suggest its high potential for cosmetic applications.