Biosynthesis and characterization of a non-repetitive polypeptide derived from silk fibroin heavy chain

Recombinant fibrous protein biomaterials meet skin tissue engineering

Natural biomaterials, particularly fibrous proteins, are extensively utilized in skin tissue engineering. However, their application is impeded by batch-to-batch variance, limited chemical or physical versatility, and environmental concerns. Recent advancements in gene editing and fermentation technology have catalyzed the emergence of recombinant fibrous protein biomaterials, which are gaining traction in skin tissue engineering. The modular and highly customizable nature of recombinant synthesis enables precise control over biomaterial design, facilitating the incorporation of multiple functional motifs. Additionally, recombinant synthesis allows for a transition from animal-derived sources to microbial sources, thereby reducing endotoxin content and rendering recombinant fibrous protein biomaterials more amenable to scalable production and clinical use. In this review, we provide an overview of prevalent recombinant fibrous protein biomaterials (collagens, elastin, silk proteins and their chimeric derivatives) used in skin tissue engineering (STE) and compare them with their animal-derived counterparts. Furthermore, we discuss their applications in STE, along with the associated challenges and future prospects.

A review on complete silk gene sequencing and de novo assembly of artificial silk

Silk, especially spider and insect silk, is a highly versatile biomaterial with potential applications in biomedicine, materials science, and biomimetic engineering. The primary structure of silk proteins is the basis for the mechanical properties of silk fibers. Biotechnologies such as single-molecule sequencing have facilitated an increasing number of reports on new silk genes and assembled silk proteins. Therefore, this review aims to provide a comprehensive overview of the recent advances in representative spider and insect silk proteins, focusing on identification methods, sequence characteristics, and de novo design and assembly. The review discusses three identification methods for silk genes: polymerase chain reaction (PCR)-based sequencing, PCR-free cloning and sequencing, and whole-genome sequencing. Moreover, it reveals the main spider and insect silk proteins and their sequences. Subsequent de novo assembly of artificial silk is covered and future research directions in the field of silk proteins, including new silk genes, customizable artificial silk, and the expansion of silk production and applications are discussed. This review provides a basis for the genetic aspects of silk production and the potential applications of artificial silk in material science and biomedical engineering.

Sustainable Bombyx mori's silk fibroin for biomedical applications as a molecular biotechnology challenge: A review

Silk is a natural engineering material with a unique set of properties. The major constituent of silk is fibroin, a protein widely used in the biomedical field because of its mechanical strength, toughness and elasticity, as well as its biocompatibility and biodegradability. The domestication of silkworms allows large amounts of fibroin to be extracted inexpensively from silk cocoons. However, the industrial extraction process has drawbacks in terms of sustainability and the quality of the final medical product. The heterologous production of fibroin using recombinant DNA technology is a promising approach to address these issues, but the production of such recombinant proteins is challenging and further optimization is required due to the large size and repetitive structure of fibroin's DNA and amino acid sequence. In this review, we describe the structure-function relationship of fibroin, the current extraction process, and some insights into the sustainability of silk production for biomedical applications. We focus on recent advances in molecular biotechnology underpinning the production of recombinant fibroin, working toward a standardized, successful and sustainable process.

Effect of degumming degree on the structure and tensile properties of RSF/RSS composite films prepared by one-step extraction

Regenerated silk fibroin (RSF) and regenerated sericin (RSS) have attracted much attention for tissue engineering due to excellent biocompatibility and controllable degradation. However, pure RSF films prepared by existing methods are brittle, which limits applications in the field of high-strength and/or flexible tissues (e.g. cornea, periosteum and dura). A series of RSF/RSS composite films were developed from solutions prepared by dissolving silks with different degumming rates. The molecular conformation, crystalline structure and tensile properties of the films and the effect of sericin content on the structure and properties were investigated. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction results revealed more β-sheets in films prepared by boiling water degumming than in Na₂CO₃-degummed RSF_C film. Analysis of mechanical properties showed that the breaking strength (3.56 MPa) and elongation (50.51%) of boiling water-degummed RSF/RSS film were significantly increased compared with RSF_C film (2.60 MPa and 32.31%), and the flexibility of films could be further improved by appropriately reducing the degumming rate.

Effect of Different Collagen on Anterior Cruciate Ligament Transection and Medial Meniscectomy-Induced Osteoarthritis Male Rats

Osteoarthritis (OA) is a common type of arthritis characterized by degeneration of the articular cartilage and joint dysfunction. Various pharmacological and non-pharmacological techniques have been used to manage these diseases. Due to the diverse therapeutic properties of marine collagen, it has received considerable attention in its pharmacological application. Thus, the purpose of this study was to compare the efficacy of jellyfish collagen, collagen peptide, other sources of marine collagen, and glycine in treating OA. In the OA rat model, an anterior cruciate ligament transection combined with medial meniscectomy surgery (ACLT + MMx) was used to induce osteoarthritis in rats. Two weeks before surgery, male Sprague-Dawley rats were fed a chow-fat diet. After 6 weeks of treatment with collagen, collagen peptide, and glycine, the results show that they could inhibit the production of proinflammatory cytokines and their derivatives, such as COX-2, MMP-13, and CTX-II levels; therefore, it can attenuate cartilage degradation. Moreover, collagen peptides can promote the synthesis of collagen type II in cartilage. These results demonstrate that collagen and glycine have been shown to have protective properties against OA cartilage degradation. In contrast, collagen peptides have been shown to show cartilage regeneration but less protective properties. Jellyfish collagen peptide at a dose of 5 mg/kg b. w. has the most significant potential for treating OA because it protects and regenerates cartilage in the knee.

Enhanced Silk Fibroin/Sericin Composite Film: Preparation, Mechanical Properties and Mineralization Activity

The periosteum plays an important role in bone formation and reconstruction. One of the reasons for the high failure rate of bone transplantation is the absence of the periosteum. Silk fibroin (SF) and silk sericin (SS) have excellent biocompatibility and physicochemical properties, which have amazing application prospects in bone tissue engineering, but lacked mechanical properties. We developed a series of SF/SS composite films with improved mechanical properties using boiling water degumming, which caused little damage to SF molecular chains to retain larger molecules. The Fourier transform infrared spectroscopy and X-ray diffraction results showed that there were more β-sheets in SF/SS films than in Na₂CO₃ degummed SF film, resulting in significantly improved breaking strength and toughness of the composite films, which were increased by approximately 1.3 and 1.7 times, respectively. The mineralization results showed that the hydroxyapatite (HAp) deposition rate on SF/SS composite films was faster than that on SF film. The SF/SS composite films effectively regulated the nucleation, growth and aggregation of HAp-like minerals, and the presence of SS accelerated the early mineralization of SF-based materials. These composite films may be promising biomaterials in the repair and regeneration of periosteum.

Gastric acid-response chitosan/alginate/tilapia collagen peptide composite hydrogel: Protection effects on alcohol-induced gastric mucosal injury

Long-term excessive alcohol intake can easily lead to gastritis, gastric ulcer, and gastric bleeding. In this paper, the gastric acid-responsive hydrogel of CS-NAC/alginate/tilapia collagen peptide (CS-NAC/ALG/TCP) was developed. Its structure and properties were determined. The alcohol-induced gastric mucosal injury models in mice were established to evaluate the protective effects of CS-NAC/ALG/TCP. The results showed that CS-NAC/ALG/TCP was successfully fabricated, and it showed a sustained release of TCP, strong mucoadhesion, and excellent biodegradability in vitro. In the animal experiments, CS-NAC/ALG/TCP improved the oxidative stress status of the gastric mucosa by increasing the levels of SOD, GSH, and CAT in tissues. It also down-regulated the expression of MPO, TNF-α, IL-1β, and IL-6, and increased the production of gastric protective factors such as PGE2 and NO in mouse stomach, thereby reducing the alcohol-induced inflammation and protecting the gastric mucosal injury. Besides, CS-NAC/ALG/TCP can also increase the activities of alcohol metabolism enzymes to improve alcohol metabolism, thereby reducing alcoholic damage. In conclusion, CS-NAC/ALG/TCP is a promising candidate for the treatment of alcohol-induced gastric injury.

Optimized preparation of gastric acid-response sulfhydryl functionalized chitosan/alginate/tilapia peptide hydrogel and its protective effects on alcohol-induced liver and brain injury

Long-term alcohol intake or drinking large quantities of alcohol at one time can cause organ damage, which in turn can lead to chronic diseases. It is of important clinical and social significance to find effective approaches for the prevention and treatment of alcohol-induced diseases. In this paper, sulfhydryl functionalized chitosan (chitosan-N-acetyl-l-cysteine, CS-NAC) and sodium alginate (SA) were used as the matrix materials to contain tilapia peptide (TP), and a gastric acid-response hydrogel (CS-NAC/SA/TP) was prepared. Taking the ethanol adsorption rate as the response index, based on the results of the single factor test, the preparation process of CS-NAC/SA/TP was optimized through the Box-Behnken design. The swelling and antioxidant properties of CS-NAC/SA/TP were tested in vitro, and the protective effects on alcohol-induced acute liver injury and chronic brain injury were assessed in vivo. Structural characterization showed that CS-NAC/SA/TP was successfully prepared. Under the optimal conditions (SA concentration of 1%, M CS-NAC/M CaCO3 of 1 : 1, M SA/M CS-NAC(CaCO3) of 15 : 1), the prepared CS-NAC/SA/TP had a porous structure, a swelling ratio of 2350%, an ethanol adsorption rate of 56.23% and strong antioxidant capacities in vitro. Animal experiment results demonstrated that CS-NAC/SA/TP effectively reduced liver and brain injuries in mice caused by alcoholism. Summarily, these findings indicate that CS-NAC/SA/TP has potential applications in preventing alcohol-induced liver and brain injuries.

Tunable High-Molecular-Weight Silk Fibroin Polypeptide Materials: Fabrication and Self-Assembly Mechanism

Silk fibroin is a multisegment natural protein composed of a heavy (H) chain, a light (L) chain and a P25 glycoprotein chain. Herein, we developed a dialysis separation technique under reducing conditions to break the disulfide bond between the H-chain and L-chain and remove the low-molecular-weight portions of the protein. Thus, a high-molecular-weight silk fibroin polypeptide (HSF) material was obtained. SDS-PAGE electrophoresis showed that the molecular weight of HSF was over 80 kDa, similar to the size of the silk fibroin H-chain. Amino acid analysis result demonstrated that the amino acid composition of HSF was almost identical to that of H-chain composition. Importantly, the HSF material obtained has a high surface activity, which can reduce the surface tension of water to below 20 mN/m; at high temperature and high concentration, it can also form a unique nanofibrous network with a lamellar crystalline structure. HSF can further form a rod-shaped structure in a strong polar environment and become a star-shaped fibrous network in a weak polar environment. When the pH value of HSF solution was adjusted from 6 to 8, a structural transition from a folded crank sheet-like structure with micellar beads to a ring-like fibrous structure was observed. During the conversion of HSF from colloidal particles to nanofibers, its molecular conformation also transformed from random coils to β-sheets. These tunable properties indicate that HSF materials have a wide range of applications in biomedical and green chemistry fields.

Sequence-structure characterization of recombinant polypeptides derived from silk fibroin heavy chain

The molecular conformation of a biomedical material plays a major role in the stability, bioactivity and controlled release of drugs. In order to identify the impact of fragments derived from Bombyx mori silk fibroin on their structures and to develop a new strategy for controlling drug release, we designed several hydrophobic-hydrophilic recombinants (GS16F1, GS16F4, and GS16F8), and investigated their molecular conformations and conformational changes induced by different storage temperatures and pH values. The results showed that the α-helix characteristic peaks were prominent in the fresh freeze-dried powder with increasing F1 repeats. During storage at 4 °C, 37 °C or 60 °C, the β-turns (especially in GS16F8) and α-helixes turned into β-sheets. The β-sheet content in the polypeptides increased with increasing temperature and F1 repeats. Following induction by different pH values, their molecular conformations changed significantly, but not the same as that of powder storage. The content of β-sheets was GS16F1 > GS16F4 > GS16F8 near the isoelectric point of each polypeptide. With increasing pH value, the β-sheet content of GS16F1 decreased more slowly compared with GS16F4 and GS16F8. These results were satisfactory for structural regulation in the field of drug controlled release research.

An RGD-Containing Peptide Derived from Wild Silkworm Silk Fibroin Promotes Cell Adhesion and Spreading

Arginine-Glycine-Aspartate (RGD) tripeptide can promote cell adhesion when present in the amino acid of proteins such as fibronectin. In order to demonstrate the bioactivity of an RGD-containing silk protein, a gene encoding the RGD motif-containing peptide GSGAGGRGDGGYGSGSS (⁻RGD⁻) derived from nonmulberry silk was designed and cloned, then multimerised and inserted into a commercial pGEX expression vector for recombinant expression of (⁻RGD⁻)n peptides. Herein, we focus on two glutathione-S-transferase (GST)-tagged fusion proteins, GST⁻(⁻RGD⁻)₄ and GST⁻(⁻RGD⁻)₈, which were expressed in Escherichia coli BL21, purified by GST affinity chromatography, and analyzed with sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and mass spectrometry (MS). Target peptides (⁻RGD⁻)₄ and (⁻RGD⁻)₈ (6.03 and 11.5 kDa) were cleaved from the GST-tag by thrombin digestion, as verified with MS and SDS-PAGE. Isoelectric point analysis confirmed that target peptides were expressed and released in accordance with the original design. Target peptides self-assembled into a mainly α-helical structure, as determined by circular dichroism spectroscopy. Furthermore, (⁻RGD⁻)₄ and (⁻RGD⁻)₈ modified mulberry silk fibroin films were more effective for rapid cell adhesion, spreading and proliferative activity of L929 cells than some chemically synthesized RGD peptides modified and mulberry silk lacking the RGD motif.

Biosynthesis and Characterization of Recombinant Silk-Like Polypeptides Derived from the Heavy Chain of Silk Fibrion

In order to investigate the impacts on the structure and biomedical function of typical fragments derived from repetitive and non-repetitive regions of the Bombyx mori silk fibroin heavy chain, several block combination genes (gs16f1, gs16f4, gs16f8, and gs16f12) were designed, cloned into a fusion protein expression vector tagged with glutathione S-transferase (GST), and expressed in Escherichia coli. Fusion proteins GST-GS16F1, GST-GS16F4, and GST-GS16F8 were purified by GST affinity chromatography, and single bands were identified by SDS-PAGE. Under optimal initial cell density, in ducer concentration and induction expression time, the yield of purified GST-GS16F1, GST-GS16F4, and GST-GS16F8 per liter of bacterial culture reached 79, 53, and 28 mg, respectively. Mass spectrometry revealed molecular weights for GST-GS16F1, GST-GS16F4, and GST-GS16F8 of 37.7, 50.0, and 65.7 kDa, respectively, consistent with the theoretical values of 37.4, 49.4, and 65.5 kDa. Similarly, measured values of pI were 5.35, 4.5, and 4.2 for the fusion proteins, consistent with predicted values of 5.34, 4.44, and 4.09. CD spectra showed the molecular conformation of GS16F1 was mainly β-sheet structure, while more stable α-helix structure formed in GS16F4 and GS16F8.

Marine Collagen Peptides from the Skin of Nile Tilapia (Oreochromis niloticus): Characterization and Wound Healing Evaluation

Burns can cause tremendous economic problems associated with irreparable harm to patients and their families. To characterize marine collagen peptides (MCPs) from the skin of Nile tilapia (Oreochromis niloticus), molecular weight distribution and amino acid composition of MCPs were determined, and Fourier transform infrared spectroscopy (FTIR) was used to analyze the chemical structure. Meanwhile, to evaluate the wound healing activity, in vitro and in vivo experiments were carried out. The results showed that MCPs prepared from the skin of Nile tilapia by composite enzymatic hydrolysis were composed of polypeptides with different molecular weights and the contents of polypeptides with molecular weights of less than 5 kDa accounted for 99.14%. From the amino acid composition, the majority of residues, accounting for over 58% of the total residues in MCPs, were hydrophilic. FTIR indicated that the main molecular conformations inside MCPs were random coil. In vitro scratch assay showed that there were significant effects on the scratch closure by the treatment of MCPs with the concentration of 50.0 μg/mL. In the experiments of deep partial-thickness scald wound in rabbits, MCPs could enhance the process of wound healing. Therefore, MCPs from the skin of Nile tilapia (O. niloticus) have promising applications in wound care.