Biosynthesis of recombinant human pro-alpha 1(III) chains in a baculovirus expression system: production of disulphide-bonded and non-disulphide-bonded species containing full-length triple helices

Green biomanufacturing in recombinant collagen biosynthesis: trends and selection in various expression systems

Collagen, classically derived from animal tissue, is an all-important protein material widely used in biomedical materials, cosmetics, fodder, food, etc. The production of recombinant collagen through different biological expression systems using bioengineering techniques has attracted significant interest in consideration of increasing market demand and the process complexity of extraction. Green biomanufacturing of recombinant collagen has become one of the focus topics. While the bioproduction of recombinant collagens (type I, II, III, etc.) has been commercialized in recent years, the biosynthesis of recombinant collagen is extremely challenging due to protein immunogenicity, yield, degradation, and other issues. The rapid development of synthetic biology allows us to perform a heterologous expression of proteins in diverse expression systems, thus optimizing the production and bioactivities of recombinant collagen. This review describes the research progress in the bioproduction of recombinant collagen over the past two decades, focusing on different expression systems (prokaryotic organisms, yeasts, plants, insects, mammalian and human cells, etc.). We also discuss the challenges and future trends in developing market-competitive recombinant collagens.

Collagen- and hyaluronic acid-based hydrogels and their biomedical applications

Hydrogels have been widely investigated in biomedical fields due to their similar physical and biochemical properties to the extracellular matrix (ECM). Collagen and hyaluronic acid (HA) are the main components of the ECM in many tissues. As a result, hydrogels prepared from collagen and HA hold inherent advantages in mimicking the structure and function of the native ECM. Numerous studies have focused on the development of collagen and HA hydrogels and their biomedical applications. In this extensive review, we provide a summary and analysis of the sources, features, and modifications of collagen and HA. Specifically, we highlight the fabrication, properties, and potential biomedical applications as well as promising commercialization of hydrogels based on these two natural polymers.

Type III collagen (COL3A1): Gene and protein structure, tissue distribution, and associated diseases

Collagen alpha-1(III) chain, also known as the alpha 1 chain of type III collagen, is a protein that in humans is encoded by the COL3A1 gene. Three alpha 1 chains are required to form the type III collagen molecule which has a long triple-helical domain. Type III collagen, an extracellular matrix protein, is synthesized by cells as a pre-procollagen. It is found as a major structural component in hollow organs such as large blood vessels, uterus and bowel. Other functions of type III collagen include interaction with platelets in the blood clotting cascade and it is also an important signaling molecule in wound healing. Mutations in the COL3A1 gene cause the vascular type of Ehlers-Danlos syndrome (vEDS; OMIM 130050). It is the most serious form of EDS, since patients often die suddenly due to a rupture of large arteries. Inactivation of the murine Col3a1 gene leads to a shorter life span in homozygous mutant mice. The mice die prematurely from a rupture of major arteries mimicking the human vEDS phenotype. The biochemical and cellular effects of COL3A1 mutations have been studied extensively. Most of the glycine mutations lead to the synthesis of type III collagen with reduced thermal stability, which is more susceptible for proteinases. Intracellular accumulation of this normally secreted protein is also found. Ultrastructural analyses have demonstrated dilated rough endoplasmic reticulum and changes in the diameter of collagen fibers. Other clinical conditions associated with type III collagen are several types of fibroses in which increased amounts of type III collagen accumulate in the target organs.

Bioengineered Collagens

There is a great deal of interest in obtaining recombinant collagen as an alternative source of material for biomedical applications and as an approach for obtaining basic structural and biological information. However, application of recombinant technology to collagen presents challenges, most notably the need for post-translational hydroxylation of prolines for triple-helix stability. Full length recombinant human collagens have been successfully expressed in cell lines, yeast, and several plant systems, while collagen fragments have been expressed in E. coli. In addition, bacterial collagen-like proteins can be expressed in high yields in E. coli and easily manipulated to incorporate biologically active sequences from human collagens. These expression systems allow manipulation of biologically active sequences within collagen, which has furthered our understanding of the relationships between collagen sequences, structure and function. Here, recombinant studies on collagen interactions with cell receptors, extracellular matrix proteins, and matrix metalloproteinases are reviewed, and discussed in terms of their potential biomaterial and biomedical applications.

Natural and Genetically Engineered Proteins for Tissue Engineering

To overcome the limitations of traditionally used autografts, allografts and, to a lesser extent, synthetic materials, there is the need to develop a new generation of scaffolds with adequate mechanical and structural support, control of cell attachment, migration, proliferation and differentiation and with bio-resorbable features. This suite of properties would allow the body to heal itself at the same rate as implant degradation. Genetic engineering offers a route to this level of control of biomaterial systems. The possibility of expressing biological components in nature and to modify or bioengineer them further, offers a path towards multifunctional biomaterial systems. This includes opportunities to generate new protein sequences, new self-assembling peptides or fusions of different bioactive domains or protein motifs. New protein sequences with tunable properties can be generated that can be used as new biomaterials. In this review we address some of the most frequently used proteins for tissue engineering and biomedical applications and describe the techniques most commonly used to functionalize protein-based biomaterials by combining them with bioactive molecules to enhance biological performance. We also highlight the use of genetic engineering, for protein heterologous expression and the synthesis of new protein-based biopolymers, focusing the advantages of these functionalized biopolymers when compared with their counterparts extracted directly from nature and modified by techniques such as physical adsorption or chemical modification.

A fusion protein of hepatocyte growth factor for immobilization to collagen

We describe here a fusion protein consisting of hepatocyte growth factor (HGF; an angiogenic factor) and a collagen-binding domain (CBD) polypeptide of fibronectin (FN). This fusion protein (CBD-HGF), produced by a baculovirus expression system, exhibited much stronger collagen binding activity than native HGF in the range of 0.4-6.4microg/ml. Its binding at the lowest concentration exceeded that of HGF at the highest concentration. In addition, the collagen-bound CBD-HGF promoted growth of endothelial cells (ECs) to a greater degree at least 4 days longer than HGF added to the culture medium; about 5-fold greater increase in cell number after 10 days. These findings suggest that the fused CBD moiety not only helped immobilize HGF on collagen but also helped stabilize the fusion molecule, resulting in prolonged activity. The angiogenic activity of CBD-HGF in animal tissues was examined by subcutaneously implanting collagen sponges containing bound CBD-HGF. Blood vessel formation in the sponges after 7 days was 4-6-fold extensive as compared to the control sponges without sample. Implanted sponges with native HGF did not show significant difference from control. These results indicate that CBD-HGF is suitable for in vitro culture of ECs, and that this fusion protein can be used to confer HGF activity on biomaterials for use in tissue engineering.

Generation of hybrid transgenic silkworms that express Bombyx mori prolyl-hydroxylase alpha-subunits and human collagens in posterior silk glands: Production of cocoons that contained collagens with hydroxylated proline residues

Prolyl 4-hydroxylase (P4H) is a heterotetramer enzyme consisting of alpha-subunits (P4Halpha) and beta-subunits (P4Hbeta), and is required for collagen biosynthesis. Previously, we generated transgenic silkworms that produced human type III collagen fragments (mini-collagens) in the posterior silk gland (PSG). However, prolyl 4-hydroxylation did not occur on the mini-collagens, because in spite of an abundant expression of P4Hbeta in PSGs, P4Halpha expression was quite low there, thus resulting in an insufficient activity of P4H. In this study we aimed at generating hybrid transgenic silkworms whose PSGs are capable of producing mini-collagens and enough P4H for their prolyl 4-hydroxylation. Isolated PSGs were bombarded with fibroin L-chain gene promoter-driven vectors containing Bombyx mori P4Halpha (BmP4Halpha) cDNAs and were transplanted into the hemolymphatic cavity. The P4H activity in the PSG cells significantly increased, indicating that the expressed BmP4Halpha formed active tetramers with endogenous BmP4Hbeta. Using germ-line transgenesis technology, silkworms were generated that synthesized BmP4Halpha in PSG cells. The P4H activity in the transgenic silkworms was 130-fold higher than that of wild-type counterparts. Finally, we generated hybrid transgenic silkworms that expressed cDNAs of both BmP4Halpha and mini-collagen in PSG cells. They spun cocoons that contained mini-collagens whose appropriate proline residues had been adequately hydroxylated.

Recombinant microbial systems for the production of human collagen and gelatin

The use of genetically engineered microorganisms is a cost-effective, scalable technology for the production of recombinant human collagen (rhC) and recombinant gelatin (rG). This review will discuss the use of yeast (Pichia pastoris, Saccharomyces cerevisiae, Hansenula polymorpha) and of bacteria (Escherichia coli, Bacillus brevis) genetically engineered for the production of rhC and rG. P. pastoris is the preferred production system for rhC and rG. Recombinant strains of P. pastoris accumulate properly hydroxylated triple helical rhC intracellularly at levels up to 1.5 g/l. Coexpression of recombinant collagen with recombinant prolyl hydroxylase results in the synthesis of hydroxylated collagen with thermal stability similar to native collagens. The purified hydroxylated rhC forms fibrils that are structurally similar to fibrils assembled from native collagen. These qualities make rhC attractive for use in many medical applications. P. pastoris can also be engineered to secrete high levels (3 to 14 g/l ) of collagen fragments with defined length, composition, and physiochemical properties that serve as substitutes for animal-derived gelatins. The replacement of animal-derived collagen and gelatin with rhC and rG will result in products with improved safety, traceability, reproducibility, and quality. In addition, the rhC and rG can be engineered to improve the performance of products containing these biomaterials.

Synthesis of prolyl 4-hydroxylase alpha subunit and type IV collagen in hemocytic granular cells of silkworm, Bombyx mori: Involvement of type IV collagen in self-defense reaction and metamorphosis

The present study shows that hemocytic granular cells synthesize and secrete type IV collagen (ColIV) in the silkworm Bombyx mori (B. mori) and suggests that these cells play roles in the formation of basement membrane, the encapsulation of foreign bodies, and the metamorphic remodeling of the gut. The full- and partial-length cDNA of B. mori prolyl 4-hydroxylase alpha subunit (BmP4Halpha) and B. mori ColIV (BmColIV) were cloned, respectively. In situ hybridization and immunocytochemistry on larval tissues and cells identified hemocytic granular cells as the cells that express mRNAs and proteins of both BmP4Halpha and BmColIV. Immunohistochemistry and immunocytochemistry demonstrated that BmColIV was present in the basement membrane and in the secretory granules of granular cells, respectively. Granular cells in culture secreted BmColIV without accompanying the degranulation and discharged it from the granules when the cells were degranulated. Nylon threads were inserted into the hemocoel of larvae. Granular cells concentrated around the nylon threads and encapsulated them as a self-defense reaction. BmColIV was found to be a component of the capsules. Furthermore, the present study showed that actively BmColIV-expressing granular cells accumulated around the midgut epithelium and formed BmColIV-rich thick basal lamina-like structures there in larval to pupal metamorphosis.

Triple helical collagen-like peptides: engineering and applications in matrix biology

Collagen, a large insoluble protein with a characteristic triple helical structure, is found as the most prominent component of extracellular matrix. The functions of collagen are not limited to providing mechanical strength to various tissues and organs as a structural protein, as it has been pointed out that collagen exhibits various biological functions through specific interactions with other macromolecules. However, the use of native triple helical collagen is often troublesome because of its insolubility and gelating properties. Instead, triple helical collagen-like peptides have been designed and are used as collagen surrogates in studies on collagen structure, stability, and biological functions including binding to other proteins and cultured cells. This article reviews recent progress in peptide design, synthesis, and the applications of collagen-like peptides in current matrix biology, while emphasizing the advantages of the peptide-based strategy.

Transgenic silkworms produce recombinant human type III procollagen in cocoons

We describe the generation of transgenic silkworms that produce cocoons containing recombinant human collagen. A fusion cDNA was constructed encoding a protein that incorporated a human type III procollagen mini-chain with C-propeptide deleted, a fibroin light chain (L-chain), and an enhanced green fluorescent protein (EGFP). This cDNA was ligated downstream of the fibroin L-chain promoter and inserted into a piggyBac vector. Silkworm eggs were injected with the vectors, producing worms displaying EGFP fluorescence in their silk glands. The cocoons emitted EGFP fluorescence, indicating that the promoter and fibroin L-chain cDNAs directed the synthesized products to be secreted into cocoons. The presence of fusion proteins in cocoons was demonstrated by immunoblotting, collagenase-sensitivity tests, and amino acid sequencing. The fusion proteins from cocoons were purified to a single electrophoretic band. This study demonstrates the viability of transgenic silkworms as a tool for producing useful proteins in bulk.

Interleukin-2-collagen chimeric protein which liberates interleukin-2 upon collagenolysis

Interleukin-2 (IL-2) is a potent activator of cellular immunity and has been utilized as an immunotherapeutic agent. We stably immobilized human IL-2 to collagen by covalently binding it to the N-terminus of human type III collagen (3A1) as IL2-3A1 chimeric protein using recombinant technology. The present study was aimed at liberating IL-2 from the immobilized chimeric protein by treating the chimera with bacterial collagenase. These IL2-3A1 chimeras were synthesized in insect cells which had been infected with baculovirus vectors carrying IL2-3A1 cDNA. The IL2-3A1 protein produced was shown to be in a pepsin-resistant triple helical structure and exhibited IL-2 activity to a similar extent as IL-2 itself. IL2-3A1 could be immobilized on the surface of plastic dishes by incubating it in the dishes. The IL-2 region of the immobilized IL2-3A1 was liberated to culture media by collagenase treatment and this freed IL-2 stimulated the growth of lined T cells. Thus, IL2-3A1 chimeric protein could be utilized as an IL-2 deliverer whose T cell mitogenic activity can be liberated by a collagenolytic environment.

Production of EGF-collagen chimeric protein which shows the mitogenic activity

Collagen has been utilized as a natural biomaterial because of its high biocompatibility, adhesiveness to cells and tissues, and biodegradability. The present study developed a recombinant technology to confer a mitogenic activity on type III collagen by fusing it to epidermal growth factor (EGF) at the collagen's N-terminus. The chimeric protein of EGF-collagen was synthesized in insect cells by the baculovirus-insect cell expression system. The fusion protein was shown to hold the triple helical conformation of collagen and the mitogenic activity of EGF. It was also demonstrated that the chimeric protein can be immobilized on tissue culture dishes as a fibrous form and in collagen fibrils without abolishing the original mitogenic activity of EGF. This fusion protein can be utilized as a biocompatible, biodegradable, and adhesive fibrous mitogen for a variety of purposes in the area of tissue engineering.

Biophysical characterization of recombinant human Bcl-2 and its interactions with an inhibitory ligand, antimycin A

Apoptosis is an essential physiological process, regulated by the family of Bcl-2-related proteins. However, the molecular mechanism by which Bcl-2 regulates apoptosis still remains elusive. Here we report the functional studies of recombinant human Bcl-2 with the deletion of 22 residues at the C-terminal membrane-anchoring region (rhBcl-2Delta22). Characterization of rhBcl-2Delta22 showed that the recombinant protein is homogeneous and monodisperse in nondenaturing solutions, stable at room temperature in the presence of a metal chelator, and an alpha-helical protein with unfolding of secondary structure at a T(m) of 62.8 degrees C. Optimal membrane pore formation by rhBcl-2Delta22 required negatively charged phospholipids. The existence of a hydrophobic groove in rhBcl-2Delta22 was demonstrated by the fluorescence enhancement of the hydrophobic ANS probe with which a pro-apoptotic Bak BH3 peptide competed. The respiratory inhibitor antimycin A also bound to the hydrophobic groove of rhBcl-2Delta22 with a K(d) of 0.82 microM. The optimal binding conformation of antimycin A was predicted from molecular docking of antimycin A with the hBcl-2 model created by homology modeling. Antimycin A selectively induces apoptosis in cells overexpressing Bcl-2, suggesting that hydrophobic groove-binding compounds may act as selective apoptotic triggers in tumor cells.

Triple helix assembly and processing of human collagen produced in transgenic tobacco plants

The use of tobacco plants as a novel expression system for the production of human homotrimeric collagen I is presented in this report. Constructs were engineered from cDNA encoding the human proalpha1(I) chain to generate transgenic tobacco plants expressing collagen I. The recombinant proalpha1(I) chains were expressed as disulfide-bonded trimers and were shown to fold into a stable homotrimeric triple helix. Moreover, the recombinant procollagen was subsequently processed to collagen as it occurs in animals. Large amounts of recombinant collagen were purified from field grown plant material. The data suggest that plants are a valuable alternative for the recombinant production of collagen for various medical and scientific purposes.

Procollagen binds to both prolyl 4-hydroxylase/protein disulfide isomerase and HSP47 within the endoplasmic reticulum in the absence of ascorbate

In cells, only properly folded procollagen trimers are secreted from the endoplasmic reticulum (ER), while improperly folded abnormal procollagens are retained within the ER. Ascorbic acid is a co-factor in procollagen hydroxylation, which in turn is required for trimer formation. We examined chaperone proteins which bound to procollagen in the absence of ascorbic acid, a model which mimics the human disease scurvy at the cellular level. We found that both prolyl 4-hydroxylase (P4-H)/protein disulfide isomerase (PDI) and HSP47 bound to procollagen in the absence of ascorbic acid. However, the binding of PDI to procollagen decreased when HSP47 was co-transfected, suggesting that HSP47 and PDI compete for binding to procollagen. These data indicate that P4-H/PDI and HSP47 have cooperative but distinct chaperone functions during procollagen biosynthesis.

Production of recombinant hydroxylated human type III collagen fragment in Saccharomyces cerevisiae

A recombinant hydroxylated fragment of human type III collagen has been produced in Saccharomyces cerevisiae by coordinated coexpression of a collagen gene fragment together with both the alpha- and beta-subunit genes for prolyl-4-hydroxylase (EC 1.14.11.2). The collagen fragment consisted of 255 residues of the helical domain and the complete C-telopeptide and C-propeptide domains. It was inserted under the control of the ethanol-inducible ADH2 promoter in a multicopy, TRP1-selectable, yeast expression vector, YEpFlag1. The prolyihydroxylase subunit genes were cloned on either side of a bidirectional galactose-inducible promoter in a low-copy minichromosome yeast expression vector, pYEUra3, which is URA3 selectable. Coordinated expression of the three different gene products after cotransformation into S. cerevisiae was detected by immunoblotting. Amino acid analysis of an immunoreactive collagen fraction demonstrated the presence of hydroxyproline, while the presence of a triple-helical domain in the collagen fragment was demonstrated by its resistance to pepsin proteolysis.

Human recombinant alpha1(V) collagen chain. Homotrimeric assembly and subsequent processing

Human embryonic kidney cells (293-EBNA) have been transfected with the full-length human alpha1 chain of collagen V using an episomal vector. High yields (15 microgram/ml) of recombinant collagen were secreted in the culture medium. In presence of ascorbate, the alpha1(V) collagen is correctly folded into a stable triple helix as shown by electron microscopy and pepsin resistance. Circular dichroism data confirm the triple-helix conformation and indicate a melting temperature of 37.5 degrees C for the recombinant homotrimer. The major secreted form is a 250-kDa polypeptide (alpha1FL). N-terminal sequencing and collagenase digestion indicate that alpha1FL retains the complete N-propeptide but lacks the C-propeptide. However, alpha1FL might undergo a further N-terminal trimming into a form (alpha1TH) corresponding to the main triple-helix domain plus the major part of the NC2 domain. This processing is different from the one of the heterotrimeric (alpha1(V))2alpha2(V) and could have some physiological relevance. Analysis of cell homogenates indicates the presence of a 280-kDa polypeptide that is disulfide-linked through its C-terminal globular domain. This C-propeptide is rapidly cleaved after secretion in the medium, giving the first evidence of a C-terminal processing of recombinant fibrillar collagens. Rotary shadowing observations not only confirm the presence of a globular domain at the N-terminal end of the molecule but reveal the presence of a kink within the triple helix in a region poor in iminoacids. This region could represent a target for proteases. Together with the thermal stability data, these results might explain the low amount of (alpha1(V))3 recovered from tissues.

Synthesis and conformational properties of a recombinant C-propeptide of human type III procollagen

A cDNA was prepared that coded for the signal peptide of type III procollagen linked to the complete C-propeptide of the protein. The cDNA was then used to express the protein in a baculovirus recombinant system. Recombinant protein was recovered as a trimer from the medium of transfected cells in a yield of 1 to 2.5 mg per liter. Mapping of peptide fragments with and without reduction indicated that the protein contained the expected interchain disulfide bonds. Analysis by circular dichroism suggested that the conformation of the protein corresponded to the native conformation. Therefore, the protein should be appropriate for further tests of its biological function and analysis of structure by X-ray diffraction.