Production of recombinant human type I procollagen trimers using a four-gene expression system in the yeast Saccharomyces cerevisiae

Production of recombinant human type I collagen homotrimers in CHO cells and their physicochemical and functional properties

Collagen is the most abundant protein in human and mammalian structures and is a component of the mammalian extracellular matrix (ECM). Recombinant collagen is a suitable alternative to native collagen extracted from animal tissue for various biomaterials. However, due to the limitations of the expression system, most recombinant collagens are collagen fragments and lack triple helix structures. In this study, Chinese hamster ovary (CHO) cells were used to express the full-length human type I collagen α1 chain (rhCol1α1). Moreover, Endo180 affinity chromatography and pepsin were used to purify pepsin-soluble rhCol1α1 (PSC1). The amino acid composition of PSC1 was closer to that of native human type I collagen, and PSC1 contained 9.1 % hydroxyproline. Analysis of the CD spectra and molecular weight distribution results revealed that PSC1 forms a stable triple helix structure that is resistant to pepsin hydrolysis and has some tolerance to MMP1, MMP2 and MMP8 hydrolysis. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) revealed that PSC1 can self-assemble into fibers at a concentration of 1 mg/ml; moreover, PSC1 can promote the proliferation and migration of NIH 3T3 cells. In conclusion, our data suggest that PSC1 is a highly similar type of recombinant collagen that may have applications in biomaterials and other medical fields.

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.

Precision cellular agriculture: The future role of recombinantly expressed protein as food

Cellular agriculture is a rapidly emerging field, within which cultured meat has attracted the majority of media attention in recent years. An equally promising area of cellular agriculture, and one that has produced far more actual food ingredients that have been incorporated into commercially available products, is the use of cellular hosts to produce soluble proteins, herein referred to as precision cellular agriculture (PCAg). In PCAg, specific animal- or plant-sourced proteins are expressed recombinantly in unicellular hosts-the majority of which are yeast-and harvested for food use. The numerous advantages of PCAg over traditional agriculture, including a smaller carbon footprint and more consistent products, have led to extensive research on its utility. This review is the first to survey proteins currently being expressed using PCAg for food purposes. A growing number of viable expression hosts and recent advances for increased protein yields and process optimization have led to its application for producing milk, egg, and muscle proteins; plant hemoglobin; sweet-tasting plant proteins; and ice-binding proteins. Current knowledge gaps present research opportunities for optimizing expression hosts, tailoring posttranslational modifications, and expanding the scope of proteins produced. Considerations for the expansion of PCAg and its implications on food regulation, society, ethics, and the environment are also discussed. Considering the current trajectory of PCAg, food proteins from any biological source can likely be expressed recombinantly and used as purified food ingredients to create novel and tailored food products.

Incorporation of Natural and Recombinant Collagen Proteins within Fmoc-Based Self-Assembling Peptide Hydrogels

Hydrogel biomaterials mimic the natural extracellular matrix through their nanofibrous ultrastructure and composition and provide an appropriate environment for cell-matrix and cell-cell interactions within their polymeric network. Hydrogels can be modified with different proteins, cytokines, or cell-adhesion motifs to control cell behavior and cell differentiation. Collagens are desirable and versatile proteins for hydrogel modification due to their abundance in the vertebrate extracellular matrix and their interactions with cell-surface receptors. Here, we report a quick, inexpensive and effective protocol for incorporation of natural, synthetic and recombinant collagens into Fmoc-based self-assembling peptide hydrogels. The hydrogels are modified through a diffusion protocol in which collagen molecules of different molecular sizes are successfully incorporated and retained over time. Characterization studies show that these collagens interact with the hydrogel fibers without affecting the overall mechanical properties of the composite hydrogels. Furthermore, the collagen molecules incorporated into the hydrogels are still biologically active and provide sites for adhesion and spreading of human fibrosarcoma cells through interaction with the α2β1 integrin. Our protocol can be used to incorporate different types of collagen molecules into peptide-based hydrogels without any prior chemical modification. These modified hydrogels could be used in studies where collagen-based substrates are required to differentiate and control the cell behavior. Our protocol can be easily adapted to the incorporation of other bioactive proteins and peptides into peptide-based hydrogels to modulate their characteristics and their interaction with different cell types.

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.

Enhanced Collagen-like Protein for Facile Biomaterial Fabrication

We present a collagen-mimetic protein of bacterial origin based upon a modified subdomain of the collagen-like Sc12 protein from Streptococcus pyogenes, as an alternative collagen-like biomaterial platform that is highly soluble, forms stable, homogeneous, fluid-like solutions at elevated concentrations, and that can be efficiently fabricated into hydrogel materials over a broad range of pH conditions. This extended bacterial collagen-like (eBCL) protein is expressed in a bacterial host and purified as a trimeric assembly exhibiting a triple helical secondary structure in its collagen-like subdomain that is stable near physiological solution conditions (neutral pH and 37 °C), as well as over a broad range of pH conditions. We also show how this sequence can be modified to include biofunctional attributes, in particular, the Arg-Gly-Asp (RGD) sequence to elicit integrin-specific cell binding, without loss of structural function. Furthermore, through the use of EDC-NHS chemistry, we demonstrate that members of this eBCL protein system can be covalently cross-linked to fabricate transparent hydrogels with high protein concentrations (at least to 20% w/w). These hydrogels are shown to possess material properties and resistance to enzymatic degradation that are comparable or superior to a type I collagen control. Moreover, such hydrogels containing the constructs with the RGD integrin-binding sequence are shown to promote the adhesion, spreading, and proliferation of C2C12 and 3T3 cells in vitro. Due to its enhanced solubility, structural stability, fluidity at elevated concentrations, ease of modification, and facility of cross-linking, this eBCL collagen-mimetic system has potential for numerous biomedical material applications, where the ease of processing and fabrication and the facility to tailor the sequence for specific biological functionality are desired.

COLLAGEN: STRUCTURE, METABOLISM, PRODUCTION AND INDUSTRIAL APPLICATION

This review presents the current scientific literature data about structure, properties, and functions of collagen, which is known as one of the most abundant human and animal proteins. The building of collagen molecule from the primary structure to submolecular formations, the main stages of its synthesis and biodegradation are briefly described. The information about collagen diversity, its features and metabolic ways in various tissues, including skin, tendons, bones, etc. is presented. The problems of pathologies caused by collagen synthesis and breakdown disorders as well as age-related changes in collagen properties and their causes are discussed. A comparative analysis of the advantages and disadvantages of collagen and its derivatives obtaining from various sources (animals, marine, and recombinant) is given. The most productive methods for collagen extraction from various tissues are shown. The concept of collagen hydrolysis conditions influence on the physicochemical properties and biological activity of the obtained products is described. The applications of collagen and its products in various fields of industrial activity, such as pharmaceutical, cosmetic industry and medicine, are discussed. Further prospective directions of fundamental and applied investigations in this area of research are outlined.

The predominant roles of the sequence periodicity in the self-assembly of collagen-mimetic mini-fibrils

Collagen fibrils represent a unique case of protein folding and self‐association. We have recently successfully developed triple‐helical peptides that can further self‐assemble into collagen‐mimetic mini‐fibrils. The 35 nm axially repeating structure of the mini‐fibrils, which is designated the d‐period, is highly reminiscent of the well‐known 67 nm D‐period of native collagens when examined using TEM and atomic force spectroscopy. We postulate that it is the pseudo‐identical repeating sequence units in the primary structure of the designed peptides that give rise to the d‐period of the quaternary structure of the mini‐fibrils. In this work, we characterize the self‐assembly of two additional designed peptides: peptide Col877 and peptide Col108rr. The triple‐helix domain of Col877 consists of three pseudo‐identical amino acid sequence units arranged in tandem, whereas that of Col108rr consists of three sequence units identical in amino acid composition but different in sequence. Both peptides form stable collagen triple helices, but only triple helices Col877 self‐associate laterally under fibril forming conditions to form mini‐fibrils having the predicted d‐period. The Co108rr triple helices, however, only form nonspecific aggregates having no identifiable structural features. These results further accentuate the critical involvement of the repeating sequence units in the self‐assembly of collagen mini‐fibrils; the actual amino acid sequence of each unit has only secondary effects. Collagen is essential for tissue development and function. This novel approach to creating collagen‐mimetic fibrils can potentially impact fundamental research and have a wide range of biomedical and industrial applications.

Advances in Plant-Derived Scaffold Proteins

Scaffold proteins form critical biomatrices that support cell adhesion and proliferation for regenerative medicine and drug screening. The increasing demand for such applications urges solutions for cost effective and sustainable supplies of hypoallergenic and biocompatible scaffold proteins. Here, we summarize recent efforts in obtaining plant-derived biosynthetic spider silk analogue and the extracellular matrix protein, collagen. Both proteins are composed of a large number of tandem block repeats, which makes production in bacterial hosts challenging. Furthermore, post-translational modification of collagen is essential for its function which requires co-transformation of multiple copies of human prolyl 4-hydroxylase. We discuss our perspectives on how the GAANTRY system could potentially assist the production of native-sized spider dragline silk proteins and prolyl hydroxylated collagen. The potential of recombinant scaffold proteins in drug delivery and drug discovery is also addressed.

Production of protein-based polymers in Pichia pastoris

Materials science and genetic engineering have joined forces over the last three decades in the development of so-called protein-based polymers. These are proteins, typically with repetitive amino acid sequences, that have such physical properties that they can be used as functional materials. Well-known natural examples are collagen, silk, and elastin, but also artificial sequences have been devised. These proteins can be produced in a suitable host via recombinant DNA technology, and it is this inherent control over monomer sequence and molecular size that renders this class of polymers of particular interest to the fields of nanomaterials and biomedical research. Traditionally, Escherichia coli has been the main workhorse for the production of these polymers, but the methylotrophic yeast Pichia pastoris is finding increased use in view of the often high yields and potential bioprocessing benefits. We here provide an overview of protein-based polymers produced in P. pastoris. We summarize their physicochemical properties, briefly note possible applications, and detail their biosynthesis. Some challenges that may be faced when using P. pastoris for polymer production are identified: (i) low yields and poor process control in shake flask cultures; i.e., the need for bioreactors, (ii) proteolytic degradation, and (iii) self-assembly in vivo. Strategies to overcome these challenges are discussed, which we anticipate will be of interest also to readers involved in protein expression in P. pastoris in general.

Squid-Inspired Tandem Repeat Proteins: Functional Fibers and Films

Production of repetitive polypeptides that comprise one or more tandem copies of a single unit with distinct amorphous and ordered regions have been an interest for the last couple of decades. Their molecular structure provides a rich architecture that can micro-phase-separate to form periodic nanostructures (e.g., lamellar and cylindrical repeating phases) with enhanced physicochemical properties via directed or natural evolution that often exceed those of conventional synthetic polymers. Here, we review programmable design, structure, and properties of functional fibers and films from squid-inspired tandem repeat proteins, with applications in soft photonics and advanced textiles among others.

The Collagen Suprafamily: From Biosynthesis to Advanced Biomaterial Development

Collagen is the oldest and most abundant extracellular matrix protein that has found many applications in food, cosmetic, pharmaceutical, and biomedical industries. First, an overview of the family of collagens and their respective structures, conformation, and biosynthesis is provided. The advances and shortfalls of various collagen preparations (e.g., mammalian/marine extracted collagen, cell-produced collagens, recombinant collagens, and collagen-like peptides) and crosslinking technologies (e.g., chemical, physical, and biological) are then critically discussed. Subsequently, an array of structural, thermal, mechanical, biochemical, and biological assays is examined, which are developed to analyze and characterize collagenous structures. Lastly, a comprehensive review is provided on how advances in engineering, chemistry, and biology have enabled the development of bioactive, 3D structures (e.g., tissue grafts, biomaterials, cell-assembled tissue equivalents) that closely imitate native supramolecular assemblies and have the capacity to deliver in a localized and sustained manner viable cell populations and/or bioactive/therapeutic molecules. Clearly, collagens have a long history in both evolution and biotechnology and continue to offer both challenges and exciting opportunities in regenerative medicine as nature's biomaterial of choice.

Molecular assembly of recombinant chicken type II collagen in the yeast Pichia pastoris

Effective treatment of rheumatoid arthritis can be mediated by native chicken type II collagen (nCCII), recombinant peptide containing nCCII tolerogenic epitopes (CTEs), or a therapeutic DNA vaccine encoding the full-length CCOL2A1 cDNA. As recombinant CCII (rCCII) might avoid potential pathogenic virus contamination during nCCII preparation or chromosomal integration and oncogene activation associated with DNA vaccines, here we evaluated the importance of propeptide and telopeptide domains on rCCII triple helix molecular assembly. We constructed pC- and pN-procollagen (without N- or C-propeptides, respectively) as well as CTEs located in the triple helical domain lacking both propeptides and telopeptides, and expressed these in yeast Pichia pastoris host strain GS115 (his4, Mut⁺) simultaneously with recombinant chicken prolyl-4-hydroxylase α and β subunits. Both pC- and pN-procollagen monomers accumulated inside P. pastoris cells, whereas CTE was assembled into homotrimers with stable conformation and secreted into the supernatants, suggesting that the large molecular weight pC-or pN-procollagens were retained within the endoplasmic reticulum whereas the smaller CTEs proceeded through the secretory pathway. Furthermore, resulting recombinant chicken type II collagen pCα1(II) can induced collagen-induced arthritis (CIA) rat model, which seems to be as effective as the current standard nCCII. Notably, protease digestion assays showed that rCCII could assemble in the absence of C- and N-propeptides or telopeptides. These findings provide new insights into the minimal structural requirements for rCCII expression and folding.

Templated Assembly of Collagen Fibers Directs Cell Growth in 2D and 3D

Collagen is widely used in tissue engineering and regenerative medicine, with many examples of collagen-based biomaterials emerging in recent years. While there are numerous methods available for forming collagen scaffolds from isolated collagen, existing biomaterial processing techniques are unable to efficiently align collagen at the microstructural level, which is important for providing appropriate cell recognition and mechanical properties. Although some attention has shifted to development of fiber-based collagen biomaterials, existing techniques for producing and aligning collagen fibers are not appropriate for large-scale fiber manufacturing. Here, we report a novel biomaterial fabrication approach capable of efficiently generating collagen fibers of appropriate sizes using a viscous solution of dextran as a dissolvable template. We demonstrate that myoblasts readily attach and align along 2D collagen fiber networks created by this process. Furthermore, encapsulation of collagen fibers with myoblasts into non-cell-adherent hydrogels promotes aligned growth of cells and supports their differentiation. The ease-of-production and versatility of this technique will support future development of advanced in vitro tissue models and materials for regenerative medicine.

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.

Fibrous proteins: At the crossroads of genetic engineering and biotechnological applications

Fibrous proteins, such as silk, elastin and collagen are finding broad impact in biomaterial systems for a range of biomedical and industrial applications. Some of the key advantages of biosynthetic fibrous proteins compared to synthetic polymers include the tailorability of sequence, protein size, degradation pattern, and mechanical properties. Recombinant DNA production and precise control over genetic sequence of these proteins allows expansion and fine tuning of material properties to meet the needs for specific applications. We review current approaches in the design, cloning, and expression of fibrous proteins, with a focus on strategies utilized to meet the challenges of repetitive fibrous protein production. We discuss recent advances in understanding the fundamental basis of structure-function relationships and the designs that foster fibrous protein self-assembly towards predictable architectures and properties for a range of applications. We highlight the potential of functionalization through genetic engineering to design fibrous protein systems for biotechnological and biomedical applications.

Co-expression of recombinant human prolyl with human collagen α1 (III) chains in two yeast systems

In this study, we co-expressed the human prolyl 4-hydroxylases (P4H) with human collagen α1 (III) (COL3A1) in an inducible system: Pichia pastoris (pPICZB), and one constitutive system: P. pastoris (pGAPZαB). The P4H catalyses the post-translational hydroxylation of proline residues in collagen strands. Conventional protein expression system such as bacteria and yeasts, which lack endogenous P4H, are not efficient for the production of recombinant collagen. In this study, the P4H gene was constructed in pGAPZαB plasmid and pPICZB plasmid respectively. These two plasmids were transformed in P. pastoris #1 that carrying COL3A1. Colony PCR analysis and sequencing after electroporation P. pastoris GS115 showed that the target gene had inserted successfully. The results of reverse transcript-qPCR, SDS-PAGE, Western blotting and LC-MS/MS analysis of the rhCOL3A1 demonstrated that the P4H was expressed successfully. Besides, it is noted that low copy number, constitutive system was suitable for hydroxylated rhCOL3A1.

SIGNIFICANCE AND IMPACT OF THE STUDY

Successful co-expression of recombinant human collagen α1 (III) (rhCOL3A1) and human prolyl 4-hydroxylases (P4H) in Picha pastoris GS115, simultaneously results in the acquisition of rhCOL3A1 with hydroxylation of proline (Hyp). Further, this experiment also discusses that the high or low copy numbers and different promoters affect the Hyp degree of rhCOL3A1. Selecting more appropriate strains can express high degree Hyp of rhCOL3A1. This work will be helpful to the collagen structure study.

Bioengineered collagens: emerging directions for biomedical materials

Mammalian collagen has been widely used as a biomedical material. Nevertheless, there are still concerns about the variability between preparations, particularly with the possibility that the products may transmit animal-based diseases. Many groups have examined the possible application of bioengineered mammalian collagens. However, translating laboratory studies into large-scale manufacturing has often proved difficult, although certain yeast and plant systems seem effective. Production of full-length mammalian collagens, with the required secondary modification to give proline hydroxylation, has proved difficult in E. coli. However, recently, a new group of collagens, which have the characteristic triple helical structure of collagen, has been identified in bacteria. These proteins are stable without the need for hydroxyproline and are able to be produced and purified from E. coli in high yield. Initial studies indicate that they would be suitable for biomedical applications.

Towards scalable production of a collagen-like protein from Streptococcus pyogenes for biomedical applications

BACKGROUND

Collagen has proved valuable as biomedical materials for a range of clinical applications, particularly in wound healing. It is normally produced from animal sources, such as from bovines, but concerns have emerged over transmission of diseases. Recombinant collagens would be preferable, but are difficult to produce. Recently, studies have shown that 'collagens' from bacteria, including Streptococcus pyogenes, can be produced in the laboratory as recombinant products, and that these are biocompatible. In the present study we have established that examples of bacterial collagens can be produced in a bioreactor with high yields providing proof of manufacture of this important group of proteins.

RESULTS

Production trials in shake flask cultures gave low yields of recombinant product, < 1 g/L. Increased yields, of around 1 g/L, were obtained when the shake flask process was transferred to a stirred tank bioreactor, and the yield was further enhanced to around 10 g/L by implementation of a high cell density fed-batch process and the use of suitably formulated fully defined media. Similar yields were obtained with 2 different constructs, one containing an introduced heparin binding domain. The best yields, of up to 19 g/L were obtained using this high cell density strategy, with an extended 24 h production time.

CONCLUSIONS

These data have shown that recombinant bacterial collagen from S. pyogenes, can be produced in sufficient yield by a scalable microbial production process to give commercially acceptable yields for broad use in biomedical applications.

Assaying proline hydroxylation in recombinant collagen variants by liquid chromatography-mass spectrometry

Background

The fabrication of recombinant collagen and its prescribed variants has enormous potential in tissue regeneration, cell-matrix interaction investigations, and fundamental biochemical and biophysical studies of the extracellular matrix. Recombinant expression requires proline hydroxylation, a post-translational modification which is critical for imparting stability and structure. However, these modifications are not native to typical bacterial or yeast expression systems. Furthermore, detection of low levels of 4-hydroxyproline is challenging with respect to selectivity and sensitivity.

Results

We have developed a new liquid chromatography-mass spectrometry (LC-MS) method to evaluate proline hydroxylation in recombinant collagen. This assay was tested in different Saccharomyces cerevisiae expression systems to evaluate the effect of gene ratio between prolyl-4-hydroxylase and collagen on the extent of hydroxylation. These systems used a human collagen III gene that was synthesized de novo from oligonucleotides. The LC-MS assay does not require derivatization, uses only picomoles of sample, and can measure proline hydroxylation levels in recombinant and native collagen ranging from approximately 0% to 40%. The hydroxylation values obtained by LC-MS are as accurate and as precise as those obtained with the conventional method of amino acid analysis.

Conclusions

A facile, derivatization-free LC-MS method was developed that accurately determines the percentage of proline hydroxylation in different yeast expression systems. Using this assay, we determined that systems with a higher collagen-to-hydroxylase gene copy ratio yielded a lower percentage of hydroxylation, suggesting that a specifically balanced gene ratio is required to obtain higher hydroxylation levels.

APPLICATIONS OF COLLAGEN IN MEDICAL DEVICES

Collagen is the most abundant natural protein found in living systems. While there is a whole family of different collagen types, each differing in sequence, the properties that make this protein so attractive as the building blocks for medical devices, are reflected largely by the unique fibrillar structure of the molecule, as well as defined functional regions that interact with the surrounding cells and other matrix components. As a commercial medical product, collagen can be part of the natural tissue used in the device, or it can be fabricated as a reconstituted product from animal or recombinant sources. Both types of uses have distinct properties that convey advantages and disadvantages to the end product. This review examines the chemistry and biology of collagen and describes some well-documented examples of collagen-based medical devices produced in one or other of these formats.

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.

Evaluation of a thin and mechanically stable collagen cell carrier

The biological function of adherent cell populations strongly depends on the physical and biochemical properties of extracellular matrix molecules. Therefore, numerous biocompatible cell carriers have been developed to specifically influence cell attachment, proliferation, cellular differentiation, and tissue formation for diverse cell culture applications and cell-based therapies. In the present study, we evaluated the mechanical and the cell biological properties of a novel, thin, and planar collagen scaffold. The cell carrier is based on fibrillar bovine collagen type I and exhibits a low material thickness coupled with a high mechanical stability as measured by tensile tests. The influence of this new biomaterial on cell viability, proliferation, and cell differentiation was analyzed using 5-bromo-2-deoxyuridine (BrdU) proliferation assay, immunocytochemistry, water-soluble tetrazolium salt-1 assay (WST-1), live cell imaging, and electron microscopy. Cell culture experiments with the human osteosarcoma cell line Saos-2, human mesenchymal stem cells, and rodent cardiomyocytes demonstrated the in vitro biocompatibility of this chemically noncrosslinked scaffold. Both the mechanical characteristics and the in vitro biocompatibility of this collagen type I carrier facilitate the engineering of thin transferable tissue constructs and offer new possibilities in the fields of cell culture techniques, tissue engineering, and regenerative medicine.

New strategy for expression of recombinant hydroxylated human-derived gelatin in Pichia pastoris KM71

Gelatin is a well-known biopolymer, and it has a long history of use mainly as a gelling agent in the food industry. This paper reports a new method for producing recombinant hydroxylated human-derived gelatin in Pichia pastoris KM71. Three independent expression cassettes encoding for specific length of gelatin, prolyl 4-hydroxylase (P4H, EC 1.14.11.2), α-subunit (αP4H), and protein-disulfide isomerase (PDI) were individually cloned in one expression vector, pPIC9K. The modified gelatin gene and two subunit genes of P4H were under the control of two different inducible promoters, namely, alcohol oxidase 1 promoter (PAOX1) and formaldehyde dehydrogenase 1 promoter (PFLD1), respectively. The results of sodium dodecylsulfate-polyacrylamide gel electrophoresis show that a recombinant gelatin was successfully expressed in P. pastoris KM71 by methanol induction. Liquid chromatography coupled with tandem mass spectrometry analysis indicates that the expressed gelatin was hydroxylated with approximately 66.7% of proline residues in the Y positions of Gly-X-Y triplets. The results of nuclear magnetic resonance spectroscopy of recombinant gelatin test show that the (1)H and (13)C spectra have many corresponding characteristic displacement peaks, and amino acids composition analysis shows that it contains hydroxyproline and its UV absorption is consistent with the characteristics of gelatin.

Secreted production of collagen-inspired gel-forming polymers with high thermal stability in Pichia pastoris

Previously, we have shown that gel-forming triblock proteins, consisting of random coil middle blocks and trimer-forming (Pro-Gly-Pro)(9) end blocks, are efficiently produced and secreted by the yeast Pichia pastoris. These end blocks had a melting temperature (T(m)) of ∼41°C (at 1.1 mM of protein). The present work reveals that an increase of T(m) to ∼74°C, obtained by extension of the end blocks to (Pro-Gly-Pro)(16), resulted in a five times lower yield and partial endoproteolytic degradation of the protein. A possible cause could be that the higher thermostability of the longer (Pro-Gly-Pro)(16) trimers leads to a higher incidence of trimers in the cell, and that this disturbs secretion of the protein. Alternatively, the increased length of the proline-rich (Pro-Gly-Pro)(n) domain may negatively influence ribosomal translation, or may result in, for example, hydrophobic aggregation or membrane-active behavior owing to the greater number of closely placed proline residues. To discriminate between these possibilities, we studied the production of molecules with randomized end blocks that are unable to form triple helices. The codon- and amino acid composition of the genes and proteins, respectively, remained unchanged. As these nontrimerizing molecules were secreted intact and at high yield, we conclude that the impaired secretion and partial degradation of the triblock with (Pro-Gly-Pro)(16) end blocks was triggered by the occurrence of intracellular triple helices. This degradation was overcome by using a yapsin 1 protease disruptant, and the intact secreted polymer was capable of forming self-supporting gels of high thermal stability.

Decoupling ferritin synthesis from free cytosolic iron results in ferritin secretion

Ferritin is a multisubunit protein that is responsible for storing and detoxifying cytosolic iron. Ferritin can be found in serum but is relatively iron poor. Serum ferritin occurs in iron overload disorders, in inflammation, and in the genetic disorder hyperferritinemia with cataracts. We show that ferritin secretion results when cellular ferritin synthesis occurs in the relative absence of free cytosolic iron. In yeast and mammalian cells, newly synthesized ferritin monomers can be translocated into the endoplasmic reticulum and transits through the secretory apparatus. Ferritin chains can be translocated into the endoplasmic reticulum in an in vitro translation and membrane insertion system. The insertion of ferritin monomers into the ER occurs under low-free-iron conditions, as iron will induce the assembly of ferritin. Secretion of ferritin chains provides a mechanism that limits ferritin nanocage assembly and ferritin-mediated iron sequestration in the absence of the translational inhibition of ferritin synthesis.

Evaluation of the immunogenicity and cell compatibility of avian collagen for biomedical applications

There have been concerns regarding the suitability of bovine collagen as a biomaterial since the emergence of bovine spongiform encephalopathy. Consequently, collagens from other species may be used if they can meet appropriate standards, including negligible or lack of immunogenicity. In this study, the potential immunogenicity of both monomeric and pepsin-solubilized chicken collagens have been compared with a commercial, pepsin-solubilized bovine collagen that is approved for biomedical implantation. All collagens were poor immunogens compared with ovalbumin. No IgE responses were detected in sera of three strains of mice, and no hypersensitivity reactions were found in guinea pigs in maximization and Buehler tests. IgG(1) antibodies were found although the titre was substantially lower than against ovalbumin. All responses in mice and rabbits were found only when immunizations were performed with adjuvant, and after multiple injections over a long period of time. The response from the monomeric chicken collagen was less than for pepsin-solubilized collagens. Collagen sponges prepared from the two chicken collagen preparations both supported the attachment and growth of mouse fibroblasts. These data indicate that chicken collagen, particularly when monomeric, may be useful in certain biomedical applications.

Recombinant human collagen and biomimetic variants using a de novo gene optimized for modular assembly

A collagen-mimetic polymer that can be easily engineered with specific cell-responsive and mechanical properties would be of significant interest for fundamental cell-matrix studies and applications in regenerative medicine. However, oligonucleotide-based synthesis of full-length collagen has been encumbered by the characteristic glycine-X-Y sequence repetition, which promotes mismatched oligonucleotide hybridizations during de novo gene assembly. In this work, we report a novel, modular synthesis strategy that yields full-length human collagen III and specifically defined variants. We used a computational algorithm that applies codon degeneracy to design oligonucleotides that favor correct hybridizations while disrupting incorrect ones for gene synthesis. The resulting recombinant polymers were expressed in Saccharomyces cerevisiae engineered with prolyl-4-hydroxylase. Our modular approach enabled mixing-and-matching domains to fabricate different combinations of collagen variants that contained different secretion signals at the N-terminus and cysteine residues imbedded within the triple-helical domain at precisely defined locations. This work shows the flexibility of our strategy for designing and assembling specifically tailored biomimetic collagen polymers with re-engineered properties.

Sandwich ELISA for quantitative detection of human collagen prolyl 4-hydroxylase

Background

We describe a method for specific, quantitative and quick detection of human collagen prolyl 4-hydroxylase (C-P4H), the key enzyme for collagen prolyl-4 hydroxylation, in crude samples based on a sandwich ELISA principle. The method is relevant to active C-P4H level monitoring during recombinant C-P4H and collagen production in different expression systems. The assay proves to be specific for the active C-P4H α₂β₂ tetramer due to the use of antibodies against its both subunits. Thus in keeping with the method C-P4H is captured by coupled to an anti-α subunit antibody magnetic beads and an anti-β subunit antibody binds to the PDI/β subunit of the protein. Then the following holoenzyme detection is accomplished by a goat anti-rabbit IgG labeled with alkaline phosphatase which AP catalyzes the reaction of a substrate transformation with fluorescent signal generation.

Results

We applied an experimental design approach for the optimization of the antibody concentrations used in the sandwich ELISA. The assay sensitivity was 0.1 ng of C-P4H. The method was utilized for the analysis of C-P4H accumulation in crude cell extracts of E. coli overexpressing C-P4H. The sandwich ELISA signals obtained demonstrated a very good correlation with the detected protein activity levels measured with the standard radioactive assay. The developed assay was applied to optimize C-P4H production in E. coli Origami in a system where the C-P4H subunits expression acted under control by different promoters. The experiments performed in a shake flask fed-batch system (EnBase^®) verified earlier observations that cell density and oxygen supply are critical factors for the use of the inducer anhydrotetracycline and thus for the soluble C-P4H yield.

Conclusions

Here we show an example of sandwich ELISA usage for quantifying multimeric proteins. The method was developed for monitoring the amount of recombinant C-P4H tetramer in crude E. coli extracts. Due to the specificity of the antibodies used in the assay against the different C-P4H subunits, the method detects the entire holoenzyme, and the signal is not disturbed by background expression of the separate subunits.

Amino acid accumulation limits the overexpression of proteins in Lactococcus lactis

BACKGROUND

Understanding the biogenesis pathways for the functional expression of recombinant proteins, in particular membrane proteins and complex multidomain assemblies, is a fundamental issue in cell biology and of high importance for future progress in structural genomics. In this study, we employed a proteomic approach to understand the difference in expression levels for various multidomain membrane proteins in L. lactis cells grown in complex and synthetic media.

METHODOLOGY/PRINCIPAL FINDINGS

The proteomic profiles of cells growing in media in which the proteins were expressed to high or low levels suggested a limitation in the availability of branched-chain amino acids, more specifically a too limited capacity to accumulate these nutrients. By supplying the cells with an alternative path for accumulation of Ile, Leu and/or Val, i.e., a medium supplement of the appropriate dipeptides, or by engineering the transport capacity for branched-chain amino acids, the expression levels could be increased several fold.

CONCLUSIONS

We show that the availability of branched chain amino acids is a critical factor for the (over)expression of proteins in L. lactis. The forward engineering of cells for functional protein production required fine-tuning of co-expression of the branched chain amino acid transporter.

Collagens as biomaterials

This paper reviews the structure, function and applications of collagens as biomaterials. The various formats for collagens, either as tissue-based devices or as reconstituted soluble collagens are discussed. The major emphasis is on the new technologies that are emerging that will lead to new and improved collagen-based medical devices. In particular, the development of recombinant collagens, especially using microorganism systems, is allowing the development of safe and reproducible collagen products. These systems also allow for the development of novel, non-natural structures, for example collagen like structures containing repeats of key functional domains or as chimeric structures where a collagen domain is covalently linked to another biologically active component.

Production of bioactive, post-translationally modified, heterotrimeric, human recombinant type-I collagen in transgenic tobacco

Collagen's biocompatibility, biodegradability and low immunogenicity render it advantageous for extensive application in pharmaceutical or biotechnological disciplines. However, typical collagen extraction from animal or cadaver sources harbors risks including allergenicity and potential sample contamination with pathogens. In this work, two human genes encoding recombinant heterotrimeric collagen type I (rhCOL1) were successfully coexpressed in tobacco plants with the human prolyl-4-hydroxylase (P4H) and lysyl hydroxylase 3 (LH3) enzymes, responsible for key posttranslational modifications of collagen. Plants coexpressing all five vacuole-targeted proteins generated intact procollagen yields of approximately 2% of the extracted total soluble proteins. Plant-extracted rhCOL1 formed thermally stable triple helical structures and demonstrated biofunctionality similar to human tissue-derived collagen supporting binding and proliferation of adult peripheral blood-derived endothelial progenitor-like cells. Through a simple, safe and scalable method of rhCOL1 production and purification from tobacco plants, this work broadens the potential applications of human recombinant collagen in regenerative medicine.

Transcriptional profiling of gene expression changes in a PACE-transfected CHO DUKX cell line secreting high levels of rhBMP-2

Chinese hamster ovary (CHO) cells are widely used in the biopharmaceutical industry for the production of recombinant human proteins including complex polypeptides such as recombinant human bone morphogenic protein 2 (rhBMP-2). Large-scale manufacture of rhBMP-2 has associated production difficulties resulting from incomplete processing of the recombinant human protein due to insufficient endogenous levels of the paired basic amino acid cleaving enzyme (PACE) in CHO. In order to resolve this issue, CHO DUKX cells expressing rhBMP-2 were transfected with the soluble version of human PACE (PACEsol) resulting in improved amino-terminal homogeneity and a fourfold increase in rhBMP-2 productivity. In this article, we present a microarray expression profile analysis comparing the parental lineage to the higher producing subclone co-expressing PACEsol using a proprietary CHO-specific microarray. Using this technology we observed 1,076 significantly different genes in the high-productivity cells co-expressing PACEsol. Following further analysis of the differentially expressed genes, the Unfolded Protein Response (UPR) component of the endoplasmic reticulum stress response pathway was identified as a key candidate for effecting increased productivity in this cell system. Several additional ER- and Golgi-localised proteins were identified which may also contribute to this effect. The results presented here support the use of large-scale microarray expression profiling as a viable and valuable route towards understanding the behaviour of bioprocess cultures in vitro.

Prolyl 4-hydroxylases, key enzymes in the synthesis of collagens and regulation of the response to hypoxia, and their roles as treatment targets

Prolyl 4-hydroxylases (P4Hs) have central roles in the synthesis of collagens and the regulation of oxygen homeostasis. The 4-hydroxyproline residues generated by the endoplasmic reticulum (ER) luminal collagen P4Hs (C-P4Hs) are essential for the stability of the collagen triple helix. Vertebrate C-P4Hs are alpha2beta2 tetramers with three isoenzymes differing in their catalytic alpha subunits. Another P4H family, the HIF-P4Hs, hydroxylates specific prolines in the alpha subunit of the hypoxia-inducible transcription factor (HIF), a master regulator of hypoxia-inducible genes, and controls its stability in an oxygen-dependent manner. The HIF-P4Hs are cytoplasmic and nuclear enzymes, likewise with three isoenzymes in vertebrates. A third vertebrate P4H type is an ER transmembrane protein that can act on HIF-alpha but not on collagens. All P4Hs require Fe2+, 2-oxoglutarate, O2, and ascorbate. C-P4Hs are regarded as attractive targets for pharmacological inhibition to control excessive collagen accumulation in fibrotic diseases and severe scarring, while HIF-P4H inhibitors are believed to have beneficial effects in the treatment of diseases such as myocardial infarction, stroke, peripheral vascular disease, diabetes, and severe anemias. Studies with P4H inhibitors in various animal models of fibrosis, anemia, and ischemia and ongoing clinical trials with HIF-P4H inhibitors support this hypothesis by demonstrating efficacy in many applications.

The structure, stability, and complex behavior of recombinant human gelatins

Gelatin prepared from animal sources is widely used as a stabilizer in vaccine formulations. The disadvantages associated with their use such as heterogeneity and allerginicity, have led to the development of recombinant human gelatins (rhGs) as a substitute. This study focuses on characterizing the structure and monitoring the physical stability of four molecular weights ( approximately 8.5, 25, 50, and 100 kDa) of rhGs as a function of temperature and pH. The information supplied should be useful in predicting the behavior of rhGs under formulation conditions. A number of spectroscopic techniques were employed in this study. Experimental results indicated that the solution properties of all four rhGs were unpredictable with micro-aggregation observed at various pH values. The 8.5 kDa rhG was found to be in a micro-aggregated state at pH 5 while the 25 kDa rhG was found to be more aggregated at pHs 5, 7, and 8. The properties of these aggregates have been analyzed as a function of temperature. The rhGs were also found to complex with the polyanion heparin through electrostatic and nonelectrostatic interactions. The stability of these complexes has been studied as a function of temperature and pH.

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.

Testing the utility of rationally engineered recombinant collagen-like proteins for applications in tissue engineering

Collagens are attractive proteins as materials for tissue engineering. Over the last decade, significant progress has been made in developing technologies for large-scale production of native-like human recombinant collagens. Yet, the rational design of customized collagen-like proteins for smart biomaterials to enhance the quality of engineered tissues has not been explored. We mapped the D4 domain of human collagen II as most critical for supporting migration of chondrocytes and used this information to genetically engineer a collagen-like protein consisting of tandem repeats of the D4 domain (mD4 collagen). This novel collagen has been utilized to fabricate a scaffold for support of chondrocytes. We determined superior qualities of cartilaginous constructs created by chondrocytes cultured in scaffolds containing the mD4 collagen in comparison to those formed by chondrocytes cultured in bare scaffolds or those coated with wild-type collagen II. Our results are a first attempt to rationally engineer collagen-like proteins with characteristics tailored for specific needs of cartilage engineering and provide a basis for rational engineering of similar proteins for a variety of biomedical applications.