In Vivo Production of scFv-Displaying Biopolymer Beads Using a Self-Assembly-Promoting Fusion Partner

Directed evolution of a genetically encoded immobilized lipase for the efficient production of biodiesel from waste cooking oil

BACKGROUND

We have recently developed a one-step, genetically encoded immobilization approach based on fusion of a target enzyme to the self-crystallizing protein Cry3Aa, followed by direct production and isolation of the fusion crystals from Bacillus thuringiensis. Using this approach, Bacillus subtilis lipase A was genetically fused to Cry3Aa to produce a Cry3Aa-lipA catalyst capable of the facile conversion of coconut oil into biodiesel over 10 reaction cycles. Here, we investigate the fusion of another lipase to Cry3Aa with the goal of producing a catalyst suitable for the conversion of waste cooking oil into biodiesel.

RESULTS

Genetic fusion of the Proteus mirabilis lipase (PML) to Cry3Aa allowed for the production of immobilized lipase crystals (Cry3Aa-PML) directly in bacterial cells. The fusion resulted in the loss of PML activity, however, and so taking advantage of its genetically encoded immobilization, directed evolution was performed on Cry3Aa-PML directly in its immobilized state in vivo. This novel strategy allowed for the selection of an immobilized PML mutant with 4.3-fold higher catalytic efficiency and improved stability. The resulting improved Cry3Aa-PML catalyst could be used to catalyze the conversion of waste cooking oil into biodiesel for at least 15 cycles with minimal loss in conversion efficiency.

CONCLUSIONS

The genetically encoded nature of our Cry3Aa-fusion immobilization platform makes it possible to perform both directed evolution and screening of immobilized enzymes directly in vivo. This work is the first example of the use of directed evolution to optimize an enzyme in its immobilized state allowing for identification of a mutant that would unlikely have been identified from screening of its soluble form. We demonstrate that the resulting Cry3Aa-PML catalyst is suitable for the recyclable conversion of waste cooking oil into biodiesel.

Direct production of a genetically-encoded immobilized biodiesel catalyst

The use of immobilized enzymes as biocatalysts has great potential to improve the efficiency and environmental sustainability of many industrial processes. Here, we report a novel approach that allows for the direct production of a highly active immobilized lipase within the bacterium Bacillus thuringiensis. Cry3Aa-lipA crystals were generated by genetically fusing Bacillus subtilis lipase A to Cry3Aa, a protein that naturally forms crystals in the bacteria. The crystal framework significantly stabilized the lipase against denaturation in organic solvents and high temperatures, resulting in a highly efficient fusion crystal that could catalyze the conversion of triacylglycerols to fatty acid methyl ester biodiesel to near-completion over 10 cycles. The simplicity and robustness of the Cry-fusion crystal (CFC) immobilization system could make it an appealing platform for generating industrial biocatalysts for multiple bioprocesses.

Bioengineered polyester beads co-displaying protein and carbohydrate-based antigens induce protective immunity against bacterial infection

The efficacy of protein and carbohydrate antigens as vaccines can be improved via particulate delivery strategies. Here, protein and carbohydrate antigens used in formulations of vaccines against Neisseria menigitidis were displayed on in vivo assembled polyester beads using a combined bioengineering and conjugation approach. An endotoxin-free mutant of Escherichia coli was engineered to produce translational fusions of antigens (Neisseria adhesin A (NadA) and factor H binding protein (fHbp) derived from serogroup B) to the polyhydroxybutyrate synthase (PhaC), in order to intracellularly assemble polyester beads displaying the respective antigens. Purified beads displaying NadA showed enhanced immunogenicity compared to soluble NadA. Both soluble and particulate NadA elicited functional antibodies with bactericidal activity associated with protective immunity. To expand the antigen repertoire and to design a more broadly protective vaccine, NadA-PhaC beads were additionally conjugated to the capsular polysaccharide from serogroup C. Co-delivery of surface displayed NadA and the capsular polysaccharide induced a strong and specific Th1/Th17 mediated immune response associated with functional bactericidal antibodies. Our findings provide the foundation for the design of multivalent antigen-coated polyester beads as suitable carriers for protein and polysaccharide antigens in order to induce protective immunity.

Engineering Bacillus megaterium for production of functional intracellular materials

BACKGROUND

Over the last 10-15 years, a technology has been developed to engineer bacterial poly(3-hydroxybutyrate) (PHB) inclusions as functionalized beads, for applications such as vaccines, diagnostics and enzyme immobilization. This has been achieved by translational fusion of foreign proteins to the PHB synthase (PhaC). The respective fusion protein mediates self-assembly of PHB inclusions displaying the desired protein function. So far, beads have mainly been produced in recombinant Escherichia coli, which is problematic for some applications as the lipopolysaccharides (LPS) co-purified with such inclusions are toxic to humans and animals.

RESULTS

In this study, we have bioengineered the formation of functional PHB inclusions in the Gram-positive bacterium Bacillus megaterium, an LPS-free and established industrial production host. As B. megaterium is a natural PHB producer, the PHB-negative strain PHA05 was used to avoid any background PHB production. Plasmid-mediated T7 promoter-driven expression of the genes encoding β-ketothiolase (phaA), acetoacetyl-CoA-reductase (phaB) and PHB synthase (phaC) enabled PHB production in B. megaterium PHA05. To produce functionalized PHB inclusions, the N- and C-terminus of PhaC was fused to four and two IgG binding Z-domains from Staphylococcus aureus, respectively. The ZZ-domain PhaC fusion protein was strongly overproduced at the surface of the PHB inclusions and the corresponding isolated ZZ-domain displaying PHB beads were found to purify IgG with a binding capacity of 40-50 mg IgG/g beads. As B. megaterium has the ability to sporulate and respective endospores could co-purify with cellular inclusions, a sporulation negative production strain was generated by disrupting the spoIIE gene in PHA05. This strain did not produce spores when tested under sporulation inducing conditions and it was still able to synthesize ZZ-domain displaying PHB beads.

CONCLUSIONS

This study provides proof of concept for the successful genetic engineering of B. megaterium as a host for the production of functionalized PHB beads. Disruption of the spoIIE gene rendered B. megaterium incapable of sporulation but particularly suitable for production of functionalized PHB beads. This sporulation-negative mutant represents an improved industrial production strain for biotechnological processes otherwise impaired by the possibility of endospore formation.

Self-assembled particulate PsaA as vaccine against Streptococcus pneumoniae infection

Streptococcus pneumoniae is a human pathogen responsible for the majority of childhood pneumonia and media otitis cases worldwide. The diversity of its capsular polysaccharides (CPS) results in more than 91 serotypes of which at least 23 are virulent. Various CPS conjugated to immunogenic carrier proteins are currently licensed and provide protection against the infection caused by the respective serotypes but not against new and emerging virulent serotypes. In this study, we considered the conserved protein antigen PsaA, the pneumococcal surface adhesin A, in order to overcome the limitations of CPS antigens. The PsaA was translationally fused to a polyhydroxybutyrate (PHB) synthase which mediated production of PsaA displayed on PHB inclusions in recombinant Escherichia coli. This suggested that the PsaA fusion to the PHB synthase did not interfere with PHB synthase activity and its ability to mediate formation of nano-sized inclusions composed of a PHB core surrounded by the PHB synthase fused to PsaA. Isolated PHB beads showed a negative surface charge. Transmission electron microscopy analysis suggested that the PsaA fusion to the PHB synthase reduced the size of PHB beads from about 500 nm to 100 nm. The integrity and antigenicity of the fusion protein attached to isolated PHB beads was confirmed by SDS-PAGE, tryptic peptide fingerprinting analysis using MALDI-TOF-MS/MS and immunoblotting using a monoclonal anti-PsaA antibody. Mice immunized with PsaA displaying PHB beads produced high and specific IgG levels dominated by IgG1 isotype. While IgG1 titer were similar between soluble and insoluble PsaA, the IgG2 titers were strongly increased upon vaccination with insoluble PsaA i.e. PsaA displayed on PHB beads. Particulate PsaA-PHB beads elicited IgG antibodies recognizing PsaA in whole cell lysates of seven different serotypes of S. pneumoniae. This study suggested that PHB beads are suitable carriers for PsaA in order to induce a significant and specific Th-2-type immune response.

Bioengineering towards self-assembly of particulate vaccines

There is an unmet demand for safe and efficient vaccines for prevention of various infectious diseases. Subunit vaccines comprise selected pathogen specific antigens are a safe alternative to whole organism vaccines. However they often lack immunogenicity. Natural and synthetic self-assembling polymers and proteins will be reviewed in view their use to encapsulate and/or display antigens to serve as immunogenic antigen carriers for induction of protective immunity. Recent advances made in in vivo assembly of antigen-displaying polyester inclusions will be a focus. Particulate vaccines are inherently immunogenic due to enhanced uptake by antigen presenting cells which process antigens mediating adaptive immune responses. Bioengineering approaches enable the design of tailor-made particulate vaccines to fine tune immune responses towards protective immunity.

Engineering Mycobacteria for the Production of Self-Assembling Biopolyesters Displaying Mycobacterial Antigens for Use as a Tuberculosis Vaccine

Tuberculosis (TB) is a disease caused by Mycobacterium tuberculosis or Mycobacterium bovis and still remains one of the world's biggest global health burdens. Recently, engineered polyhydroxyalkanoate (PHA) biobeads that were produced in both Escherichia coli and Lactococcus lactis and displayed mycobacterial antigens were found to induce significant cell-mediated immune responses in mice. We observed that such PHA beads contained host cell proteins as impurities, which we hypothesized to have the potential to induce immunity. In this study, we aimed to develop PHA beads produced in mycobacteria (mycobacterial PHA biobeads [MBB]) and test their potential as a TB vaccine in a mouse model. As a model organism, nonpathogenic Mycobacterium smegmatis was engineered to produce MBB or MBB with immobilized mycobacterial antigens Ag85A and ESAT-6 on their surface (A:E-MBB). Three key enzymes involved in the poly(3-hydroxybutyric acid) pathway, namely, β-ketothiolase (PhaA), acetoacetyl-coenzyme A reductase (PhaB), and PHA synthase (PhaC), were engineered into E. coli-Mycobacterium shuttle plasmids and expressed in trans. Immobilization of specific antigens to the surface of the MBB was achieved by creating a fusion with the PHA synthase which remains covalently attached to the polyester core, resulting in PHA biobeads displaying covalently immobilized antigens. MBB, A:E-MBB, and an M. smegmatis vector control (MVC) were used in a mouse immunology trial, with comparison to phosphate-buffered saline (PBS)-vaccinated and Mycobacterium bovis BCG-vaccinated groups. We successfully produced MBB and A:E-MBB and used them as vaccines to induce a cellular immune response to mycobacterial antigens.

IMPORTANCE Tuberculosis (TB) is a disease caused by Mycobacterium tuberculosis or Mycobacterium bovis and still remains one of the world's biggest global health burdens. In this study, we produced polyhydroxyalkanoate (PHA) biobeads in mycobacteria and used them as vaccines to induce a cellular immune response to mycobacterial antigens.

Bioengineering a bacterial pathogen to assemble its own particulate vaccine capable of inducing cellular immunity

Many bacterial pathogens naturally form cellular inclusions. Here the immunogenicity of polyhydroxyalkanoate (PHA) inclusions and their use as particulate vaccines delivering a range of host derived antigens was assessed. Our study showed that PHA inclusions of pathogenic Pseudomonas aeruginosa are immunogenic mediating a specific cell-mediated immune response. Protein engineering of the PHA inclusion forming enzyme by translational fusion of epitopes from vaccine candidates outer membrane proteins OprI, OprF, and AlgE mediated self-assembly of PHA inclusions coated by these selected antigens. Mice vaccinated with isolated PHA inclusions produced a Th1 type immune response characterized by antigen-specific production of IFN-γ and IgG2c isotype antibodies. This cell-mediated immune response was found to be associated with the production of functional antibodies reacting with cells of various P. aeruginosa strains as well as facilitating opsonophagocytic killing. This study showed that cellular inclusions of pathogenic bacteria are immunogenic and can be engineered to display selected antigens suitable to serve as particulate subunit vaccines against infectious diseases.

Applications of Microbial Biopolymers in Display Technology

Microorganisms produce a variety of different polymers such as polyamides, polysaccharides, and polyesters. The polyesters, the polyhydroxyalkanoates (PHAs), are the most extensively studied polymers in regard to their use in display technology. The material properties of bacterial PHAs in combination with their biocompatibility and biodegradability make them attractive substrates for use in display technology applications. By translationally fusing bioactive molecules to a gene encoding a PHA-binding domain, the appropriate functionalization for a given application can be achieved such that the need for chemical immobilization is circumvented. By separately extracting and processing the biopolymer, using it to coat a surface, and then treating this surface with the fusion proteins, surface functionalization for immunodiagnostic microarray or tissue engineering applications can be accomplished. Conversely, by expressing the fusion protein directly in the PHA-producing organisms, one-step production of functionalized beads can be achieved. Such beads have been demonstrated in diverse applications, including fluorescence-activated cell sorting, enzyme-linked immunosorbent assays, microarrays, diagnostic skin test for tuberculosis, vaccines, protein purification, and affinity bioseparation.

Self-Assembled Protein-Coated Polyhydroxyalkanoate Beads: Properties and Biomedical Applications

Polyhydroxyalkanoates (PHAs) are biological polyesters that can be naturally produced by a range of bacteria as water-insoluble inclusions composed of a PHA core coated with PHA synthesis, structural, and regulatory proteins. These naturally self-assembling shell-core particles have been recently conceived as biomaterials that can be bioengineered as biologically active beads for medical applications. Protein engineering of PHA-associated proteins enabled the production of PHA-protein assemblies exhibiting biologically active protein-based functions relevant for applications as vaccines or diagnostics. Here we provide an overview of the recent advances in bioengineering of PHA particles toward the display of biomedically relevant protein functions such as selected disease-specific antigens as diagnostic tools or for the design of particulate subunit vaccines against infectious diseases such as tuberculosis, meningitis, pneumonia, and hepatitis C.

Coupled reactions on bioparticles: Stereoselective reduction with cofactor regeneration on PhaC inclusion bodies

Chiral alcohols are important building blocks for specialty chemicals and pharmaceuticals. The production of chiral alcohols from ketones can be carried out stereo selectively with alcohol dehydrogenases (ADHs). To establish a process for cost-effective enzyme immobilization on solid phase for application in ketone reduction, we used an established enzyme pair consisting of ADH from Rhodococcus erythropolis and formate dehydrogenase (FDH) from Candida boidinii for NADH cofactor regeneration and co-immobilized them on modified poly-p-hydroxybutyrate synthase (PhaC)-inclusion bodies that were recombinantly produced in Escherichia coli cells. After separate production of genetically engineered and recombinantly produced enzymes and particles, cell lysates were combined and enzymes endowed with a Kcoil were captured on the surface of the Ecoil presenting particles due to coiled-coil interaction. Enzyme-loaded particles could be easily purified by centrifugation. Total conversion of 4'-chloroacetophenone to (S)-4-chloro-α-methylbenzyl alcohol could be accomplished using enzyme-loaded particles, catalytic amounts of NAD(+) and formate as substrates for FDH. Chiral GC-MS analysis revealed that immobilized ADH retained enantioselectivity with 99 % enantiomeric excess. In conclusion, this strategy may become a cost-effective alternative to coupled reactions using purified enzymes.

A novel N-terminal region of the membrane β-hexosyltransferase: its role in secretion of soluble protein by Pichia pastoris

The β-hexosyltransferase (BHT) from Sporobolomyces singularis is a membrane-bound enzyme that catalyses transgalactosylation reactions to synthesize galacto-oligosaccharides (GOSs). To increase the secretion of the active soluble version of this protein, we examined the uncharacterized novel N-terminal region (amino acids 1-110), which included two predicted endogenous structural domains. The first domain (amino acids 1-22) may act as a classical leader while a non-classical signal was located within the remaining region (amino acids 23-110). A functional analysis of these domains was performed by evaluating the amounts of the rBHT forms secreted by recombinant P. pastoris strains carrying combinations of the predicted structural domains and the α mating factor (MFα) from Saccharomyces cerevisiae as positive control. Upon replacement of the leader domain (amino acids 1-22) by MFα (MFα-rBht(23-594)), protein secretion increased and activity of both soluble and membrane-bound enzymes was improved 53- and 14-fold, respectively. Leader interference was demonstrated when MFα preceded the putative classical rBHT(1-22) leader (amino acids 1-22), explaining the limited secretion of soluble protein by P. pastoris (GS115 : : MFα-rBht(1-594)). To validate the role of the N-terminal domains in promoting protein secretion, we tested the domains using a non-secreted protein, the anti-β-galactosidase single-chain variable antibody fragment scFv13R4. The recombinants carrying chimeras of the N-terminal 1-110 regions of rBHT preceding scFv13R4 correlated with the secretion strength of soluble protein observed with the rBHT recombinants. Finally, soluble bioactive HIS-tagged and non-tagged rBHT (purified to homogeneity) obtained from the most efficient recombinants (GS115 : : MFα-rBht(23-594)-HIS and GS115 : : MFα-rBht(23-594)) showed comparable activity rates of GOS generation.

Smart polyhydroxyalkanoate nanobeads by protein based functionalization

The development of innovative medicines and personalized biomedical approaches calls for new generation easily tunable biomaterials that can be manufactured applying straightforward and low-priced technologies. Production of functionalized bacterial polyhydroxyalkanoate (PHA) nanobeads by harnessing their natural carbon-storage granule production system is a thrilling recent development. This branch of nanobiotechnology employs proteins intrinsically binding the PHA granules as tags to immobilize recombinant proteins of interest and design functional nanocarriers for wide range of applications. Additionally, the implementation of new methodological platforms regarding production of endotoxin free PHA nanobeads using Gram-positive bacteria opened new avenues for biomedical applications. This prompts serious considerations of possible exploitation of bacterial cell factories as alternatives to traditional chemical synthesis and sources of novel bioproducts that could dramatically expand possible applications of biopolymers.

From the Clinical Editor

In the 21st century, we are coming into the age of personalized medicine. There is a growing use of biomaterials in the clinical setting. In this review article, the authors describe the use of natural polyhydroxyalkanoate (PHA) nanoparticulates, which are formed within bacterial cells and can be easily functionalized. The potential uses would include high-affinity bioseparation, enzyme immobilization, protein delivery, diagnostics etc. The challenges of this approach remain the possible toxicity from endotoxin and the high cost of production.

In vivo self-assembly of fluorescent protein microparticles displaying specific binding domains

In this study, fluorescent proteins (FPs) were engineered to self-assemble into protein particles inside recombinant Escherichia coli while mediating the display of various protein functionalities such as maltose binding protein or IgG binding domains of Protein A or G, respectively. Escherichia coli produced functional FP particles of up to 30% of cellular dry weight. The use of respective FP particles displaying certain binding domains in diagnostics and as bioseparation resins was demonstrated by direct comparison to commercial offerings. It was demonstrated that variable extensions (AVTS, FHKP, LAVG, or TS) of the N-terminus of FPs (GFP, YFP, CFP, HcRed) in combination with large C-terminal extensions such as translational fusion of the polyester synthase from Ralstonia eutropha or an aldolase from Escherichia coli led to extensive intracellular self-assembly of strongly fluorescent fusion protein particles of oval shape (0.5×1 μm). The strong fluorescent label of these bioparticles in combination with covalent display of protein functions provides a molecular toolbox for the design of self-assembled microparticles suitable for antibody-capture or ligand binding based diagnostic assays as well as the high affinity purification of target compounds such as antibodies.

Bioengineering of bacteria to assemble custom-made polyester affinity resins

Proof of concept for the in vivo bacterial production of a polyester resin displaying various customizable affinity protein binding domains is provided. This was achieved by engineering various protein binding domains into a bacterial polyester-synthesizing enzyme. Affinity binding domains based on various structural folds and derived from molecular libraries were used to demonstrate the potential of this technique. Designed ankyrin repeat proteins (DARPins), engineered OB-fold domains (OBodies), and VHH domains from camelid antibodies (nanobodies) were employed. The respective resins were produced in a single bacterial fermentation step, and a simple purification protocol was developed. Purified resins were suitable for most lab-scale affinity chromatography purposes. All of the affinity domains tested produced polyester beads with specific affinity for the target protein. The binding capacity of these affinity resins ranged from 90 to 600 nmol of protein per wet gram of polyester affinity resin, enabling purification of a recombinant protein target from a complex bacterial cell lysate up to a purity level of 96% in one step. The polyester resin was efficiently produced by conventional lab-scale shake flask fermentation, resulting in bacteria accumulating up to 55% of their cellular dry weight as polyester. A further proof of concept demonstrating the practicality of this technique was obtained through the intracellular coproduction of a specific affinity resin and its target. This enables in vivo binding and purification of the coproduced "target protein." Overall, this study provides evidence for the use of molecular engineering of polyester synthases toward the microbial production of specific bioseparation resins implementing previously selected binding domains.

Novel particulate vaccines utilizing polyester nanoparticles (bio-beads) for protection against Mycobacterium bovis infection - a review

Bovine tuberculosis (TB) continues to be a major health problem in cattle and development of a safe effective vaccine to control TB in cattle would be very useful. This paper reviews progress and provides new data in development of a TB bio-bead vaccine based on polyester nanoparticle inclusions which were produced by bioengineered bacteria. Polyhydroxybutyrate (PHB) biopolyester nanoparticles (bio-beads) have been produced which displayed mycobacterial antigens, Ag85A and ESAT-6, on the surface of the bio-beads for use as vaccines for the control of tuberculosis. Bio-beads were purified from the host production bacteria, Escherichia coli and the generally regarded as safe (GRAS) bacterium, Lactococcus lactis. Previous published studies showed that vaccination with Ag85A/ESAT-6 bio-beads induced antigen-specific IFN-γ, IL-17A, IL-6, TNF-α and IL-2 in splenocytes, but no significant increase in IL-4, IL-5 or IL-10. New results showed that antigen-specific IFN-γ release was induced by both CD4 and CD8 T cells in mice vaccinated with the Ag85A/ESAT-6 bio-beads. Mice vaccinated with Ag85A/ESAT-6 bio-beads alone or in combination with BCG had significantly lower bacterial counts from the lungs and spleen following aerosol challenge with Mycobacterium bovis compared to control groups. This unique approach to the design and production of bacterial-derived bio-beads displaying antigens enables a cost-effective way to express a diverse antigen repertoire for use as vaccines to combat TB or other diseases.

Engineering bacteria to manufacture functionalized polyester beads

The ability to generate tailor-made, functionalized polyester (polyhydroxyalkanoate, PHA) beads in bacteria by harnessing their natural carbon-storage granule production system is an exciting recent development. Proteins that naturally attach to the polyester granule core were rationally engineered to enable in vivo production of PHA beads which are applicable in bioseparation, protein purification, enzyme immobilization and diagnostics and which show advantageous properties toward the development of safe and efficient particulate vaccines. These beads are recombinantly produced as fully functional, insoluble polyester inclusions that can be easily separated from the cell. This simple one-step production of functionalized beads provides a tantalizing alternative to current commercial functional beads, for which proteins must be expressed, purified and then chemically attached to solid supports. The recent success in generating antigen-displaying PHA granules in the food-grade bacterium Lactococcus lactis capable of mediating protective immunity against Mycobacterium tuberculosis infection highlights the promise and flexibility of this new technology.

Immobilization of organophosphohydrolase OpdA from Agrobacterium radiobacter by overproduction at the surface of polyester inclusions inside engineered Escherichia coli

Organophosphorus pesticides (OP) are highly toxic and are widely used as insecticides. Bacterial organophosphohydrolases which hydrolyze a variety of OPs have been considered for the clean-up of polluted environments. This study describes the engineering of Escherichia coli towards the overproduction of the organophosphohydrolase (OpdA) from Agrobacterium radiobacter at the surface of polyester inclusions. The OpdA was N-terminally fused via a designed linker region to the C-terminus of polyester inclusion-forming enzyme PhaC of Ralstonia eutropha. The PhaC-L-OpdA fusion protein was overproduced by using the strong T7 promoter and when coexpressed with genes phaA (encoding β-ketothiolase) and phaB (encoding acetoacetyl-CoA reductase) from R. eutropha this led to formation of polyester inclusions abundantly displaying OpdA. These OpdA beads showed organophosphohydrolase activity of 1,840 U/g wet polyester beads or 4,412 U/g protein. Steady state kinetics revealed that when compared with free OpdA the k(cat) (s(-1)) of 139 of immobilized OpdA was reduced by about 16.5-fold while the K(M) (M) of 2.5 × 10(-4) was increased by 1.6-fold. The immobilized OpdA showed increased temperature stability. Moreover, the stability of OpdA immobilized to polyester beads was assessed by incubating OpdA beads at 25°C for up to 11 days and no significant loss in enzyme activity was detected. The application performance of the OpdA beads with respect to hydrolysis of OPs in contaminated environments was demonstrated in wool scour spiked with fluorescent coumaphos. This study demonstrated a new strategy toward the efficient recombinant production of immobilized organophosphohydrolase, the OpdA, suitable for bioremediation applications.

Production of a particulate hepatitis C vaccine candidate by an engineered Lactococcus lactis strain

Vaccine delivery systems based on display of antigens on bioengineered bacterial polyester inclusions can stimulate cellular immune responses. The food-grade Gram-positive bacterium Lactococcus lactis was engineered to produce spherical polyhydroxybutyrate (PHB) inclusions which abundantly displayed the hepatitis C virus core (HCc) antigen. In mice, the immune response induced by this antigen delivery system was compared to that induced by vaccination with HCc antigen displayed on PHB beads produced in Escherichia coli, to PHB beads without antigen produced in L. lactis or E. coli, or directly to the recombinant HCc protein. Vaccination site lesions were minimal in all mice vaccinated with HCc PHB beads or recombinant protein, all mixed in the oil-in-water adjuvant Emulsigen, while vaccination with the recombinant protein in complete Freund's adjuvant produced a marked inflammatory reaction at the vaccination site. Vaccination with the PHB beads produced in L. lactis and displaying HCc antigen produced antigen-specific cellular immune responses with significant release of gamma interferon (IFN-γ) and interleukin-17A (IL-17A) from splenocyte cultures and no significant antigen-specific serum antibody, while the PHB beads displaying HCc but produced in E. coli released IFN-γ and IL-17A as well as the proinflammatory cytokines tumor necrosis factor alpha (TNF-α) and IL-6 and low levels of IgG2c antibody. In contrast, recombinant HCc antigen in Emulsigen produced a diverse cytokine response and a strong IgG1 antibody response. Overall it was shown that L. lactis can be used to produce immunogenic PHB beads displaying viral antigens, making the beads suitable for vaccination against viral infections.

Relevant uses of surface proteins--display on self-organized biological structures

Proteins are often found attached to surfaces of self‐assembling biological units such as whole microbial cells or subcellular structures, e.g. intracellular inclusions. In the last two decades surface proteins were identified that could serve as anchors for the display of foreign protein functions. Extensive protein engineering based on structure–function data enabled efficient display of technically and/or medically relevant protein functions. Small size, diversity of the anchor protein as well as support structure, genetic manipulability and controlled cultivation of phages, bacterial cells and yeasts contributed to the establishment of designed and specifically functionalized tools for applications as sensors, catalysis, biomedicine, vaccine development and library‐based screening technologies. Traditionally, phage display is employed for library screening but applications in biomedicine and vaccine development are also perceived. For some diagnostic purposes phages are even too small in size so other carrier materials where needed and gave way for cell and yeast display. Only recently, intracellular inclusions such as magnetosomes, polyhydroxyalkanoate granules and lipid bodies were conceived as stable subcellular structures enabling the display of foreign protein functions and showing potential as specific and tailor‐made devices for medical and biotechnological applications.

Recombinant protein production by in vivo polymer inclusion display

A novel approach to produce purified recombinant proteins was established. The target protein is produced as polyhydroxyalkanoate (PHA) synthase fusion protein, which mediates intracellular formation of PHA inclusions displaying the target protein. After isolation of the PHA inclusions, the pure target protein was released by simple enterokinase digestion.

In vitro self-assembly of gold nanoparticle-coated poly(3-hydroxybutyrate) granules exhibiting plasmon-induced thermo-optical enhancements

Polyhydroxyalkanoate (PHA) synthase attached to gold nanoparticles (AuNP) produce poly(3-hydroxybutyrate) (PHB) upon the addition of 3-hydroxybutyrate-CoA, and then coalesce to form micrometer-sized AuNP-coated PHB granules. These AuNP-coated PHB granules are potential theranostic agents that have enhanced imaging capabilities and are capable of heating upon near-infrared laser irradiation. The AuNP-coated PHB exhibited 11-fold enhancement in surface-enhanced Raman scattering over particles prior polymerization. Stained AuNP-coated PHB exhibited a 6-fold enhancement in fluorescence intensity as well as a 1.3-fold decrease in photobleaching rate compared to PHB granules alone. The granules were also shown to emit heat when illuminated at 808 nm with a 3.9-fold increase in heating rate compared to particles alone.

Carrier-free immobilized enzymes for biocatalysis

Methods for the preparation of carrier-free insoluble enzymes are reviewed. The technology of cross-linked enzyme aggregates has now been applied to a range of synthetically useful activities. Fusion proteins are also gaining momentum because they allow a relatively selective aggregation or even a specific self-assembly of the desired enzyme activity into insoluble particles in the absence of potentially denaturing chemicals required for precipitation and cross-linking. Recycling of insoluble protein particles for multiple rounds of batchwise reaction has been demonstrated in selected biotransformations. However, for application in a fully continuous biocatalytic process, low resistance to mechanical stress and high compressibility are issues for consideration on carrier-free enzyme particles.

Bacterial polyester inclusions engineered to display vaccine candidate antigens for use as a novel class of safe and efficient vaccine delivery agents

Bioengineered bacterial polyester inclusions have the potential to be used as a vaccine delivery system. The biopolyester beads were engineered to display a fusion protein of the polyester synthase PhaC and the two key antigens involved in immune response to the infectious agent that causes tuberculosis, Mycobacterium tuberculosis, notably antigen 85A (Ag85A) and the 6-kDa early secreted antigenic target (ESAT-6) from Mycobacterium tuberculosis. Polyester beads displaying the respective fusion protein at a high density were successfully produced (henceforth called Ag85A-ESAT-6 beads) by recombinant Escherichia coli. The ability of the Ag85A-ESAT-6 beads to enhance mouse immunity to the displayed antigens was investigated. The beads were not toxic to the animals, as determined by weight gain and absence of lesions at the inoculation site in immunized animals. In vivo injection of the Ag85A-ESAT-6 beads in mice induced significant humoral and cell-mediated immune responses to both Ag85A and ESAT-6. Vaccination with Ag85A-ESAT-6 beads was efficient at stimulating immunity on their own, and this ability was enhanced by administration of the beads in an oil-in-water emulsion. In addition, vaccination with the Ag85A-ESAT-6 beads induced significantly stronger humoral and cell-mediated immune responses than vaccination with an equivalent dose of the fusion protein Ag85A-ESAT-6 alone. The immune response induced by the beads was of a mixed Th1/Th2 nature, as assessed from the induction of the cytokine gamma interferon (Th1 immune response) and increased levels of immunoglobulin G1 (Th2 immune response). Hence, engineered biopolyester beads displaying foreign antigens represent a new class of versatile, safe, and biocompatible vaccines.

Tolerance of the Ralstonia eutropha class I polyhydroxyalkanoate synthase for translational fusions to its C terminus reveals a new mode of functional display

Here, the class I polyhydroxyalkanoate synthase (PhaC) from Ralstonia eutropha was investigated regarding the functionality of its conserved C-terminal region and its ability to tolerate translational fusions to its C terminus. MalE, the maltose binding protein, and green fluorescent protein (GFP) were considered reporter proteins to be translationally fused to the C terminus. Interestingly, PhaC remained active only when a linker was inserted between PhaC and MalE, whereas MalE was not functional. However, the extension of the PhaC N terminus by 458 amino acid residues was required to achieve a functionality of MalE. These data suggested a positive interaction of the extended N terminus with the C terminus. To assess whether a linker and/or N-terminal extension is generally required for a functional C-terminal fusion, GFP was fused to the C terminus of PhaC. Both fusion partners were active without the requirement of a linker and/or N-terminal extension. A further reporter protein, the immunoglobulin G binding ZZ domain of protein A, was translationally fused to the N terminus of the fusion protein PhaC-GFP and resulted in a tripartite fusion protein mediating the production of polyester granules displaying two functional protein domains.

Production of functionalized biopolyester granules by recombinant Lactococcus lactis

Many bacteria are naturally capable of accumulating biopolyesters composed of 3-hydroxy fatty acids as intracellular inclusions, which serve as storage granules. Recently, these inclusions have been considered as nano-/microbeads with surface-attached proteins, which can be engineered to display various protein-based functions that are suitable for biotechnological and biomedical applications. In this study, the food-grade, generally-regarded-as-safe gram-positive organism Lactococcus lactis was engineered to recombinantly produce the biopolyester poly(3-hydroxybutyrate) and the respective intracellular inclusions. The codon-optimized polyhydroxybutyrate biosynthesis operon phaCAB from Cupriavidus necator was expressed using the nisin-controlled gene expression system. Recombinant L. lactis accumulated up to 6% (wt/wt) poly(3-hydroxybutyrate) of cellular dry weight. Poly(3-hydroxybutyrate) granules were isolated and analyzed with respect to bound proteins using biochemical methods and with respect to shape/size using transmission electron microscopy. The immunoglobulin G (IgG) binding ZZ domain of Staphylococcus aureus protein A was chosen as an exemplary functionality to be displayed at the granule surface by fusing it to the N terminus of the granule-associated poly(3-hydroxybutyrate) synthase. The presence of the fusion protein at the surface of isolated granules was confirmed by peptide fingerprinting using matrix-assisted laser desorption ionization-time of flight (mass spectrometry). The functionality of the ZZ domain-displaying granules was demonstrated by enzyme-linked immunosorbent assay and IgG affinity purification. In both assays, the ZZ beads from recombinant L. lactis performed at least equally to ZZ beads from Escherichia coli. Overall, in this study it was shown that recombinant L. lactis can be used to manufacture endotoxin-free poly(3-hydroxybutyrate) beads with surface functionalities that are suitable for biomedical applications.

ZZ polyester beads: an efficient and simple method for purifying IgG from mouse hybridoma supernatants

ZZ polyester beads are polyhydroxyalkanoate granules which display, at high density, the ZZ domain of protein A as a fusion protein covalently linked to the polyester core. These granules are produced directly, in one step, by recombinant E. coli. We have used these granules produced in a one step process to purify mouse IgG1, IgG2a and IgG2b from mouse hybridoma supernatants. Purified immunoglobulins were analysed by enzyme-linked immonosorbent assay, agarose gel electrophoresis and SDS-PAGE. The results showed that the recovery of IgG is 70% or greater with a significant degree of purity. ZZ polyester beads hence offer a rapid and novel method to purify IgG from mouse hybridoma culture supernatants. As a negative control we used culture supernatant from an IgM secreting hybridoma and showed that it did not bind to ZZ polyester beads.

One-step production of immobilized alpha-amylase in recombinant Escherichia coli

Industrial enzymes are often immobilized via chemical cross-linking onto solid supports to enhance stability and facilitate repeated use in bioreactors. For starch-degrading enzymes, immobilization usually places constraints on enzymatic conversion due to the limited diffusion of the macromolecular substrate through available supports. This study describes the one-step immobilization of a highly thermostable alpha-amylase (BLA) from Bacillus licheniformis and its functional display on the surface of polyester beads inside engineered Escherichia coli. An optimized BLA variant (Termamyl) was N-terminally fused to the polyester granule-forming enzyme PhaC of Cupriavidus necator. The fusion protein lacking the signal sequence mediated formation of stable polyester beads exhibiting alpha-amylase activity. The alpha-amylase beads were assessed with respect to alpha-amylase activity, which was demonstrated qualitatively and quantitatively. The immobilized alpha-amylase showed Michaelis-Menten enzyme kinetics exerting a V(max) of about 506 mU/mg of bead protein with a K(m) of about 5 microM, consistent with that of free alpha-amylase. The stability of the enzyme at 85 degrees C and the capacity for repeated usage in a starch liquefaction process were also demonstrated. In addition, structural integrity and functionality of the beads at extremes of pH and temperature, demonstrating their suitability for industrial use, were confirmed by electron microscopy and protein/enzyme analysis. This study proposes a novel, cost-effective method for the production of immobilized alpha-amylase in a single step by using the polyester granules forming protein PhaC as a fusion partner in engineered E. coli.

Multifunctional inorganic-binding beads self-assembled inside engineered bacteria

Multifunctional shell-core nano/microbeads with a hydrophobic biopolymer core and a designed protein coat for selective binding of an inorganic substance and antibodies were self-assembled inside engineered bacteria. Hybrid genes were constructed to produce tailormade bead-coating proteins in the bacterium Escherichia coli. These fusion proteins contained a binding peptide for an inorganic material, the antibody binding ZZ domain, and a self-assembly promoting as well as biopolymer synthesizing enzyme. Production of these multidomain fusion proteins inside E. coli resulted in self-assembly of beads comprising a biopolyester core and displaying covalently bound binding sites for specific and selective binding of an inorganic substance and any antibody belonging to the immunoglobulin G class. Engineered beads were isolated and purified from the respective E. coli cells by standard cell disruption procedures. Bead morphology and the binding functionalities displayed at the bead surface were assessed by the enzyme-linked immunosorbent assay, transmission electron microscopy, elemental analysis, backscattering electron density, analytical density ultracentrifugation, and atomic force microscopy. These analyses showed that bacteria can be engineered to produce fusion proteins mediating self-assembly of spherical biopolymer beads with binding affinity to gold and/or silica and antibodies. Spherical structures of this type could conceivably serve as nano/microdevices for bioimaging in medical approaches where an antibody mediated targeted delivery of an inorganic contrast agent would be desired.