• Crystal structure of -aconitate decarboxylase reveals the impact of naturally occurring human mutations on itaconate synthesis.

      Chen, Fangfang; Lukat, Peer; Iqbal, Azeem Ahmed; Saile, Kyrill; Kaever, Volkhard; van den Heuvel, Joop; Blankenfeldt, Wulf; Büssow, Konrad; Pessler, Frank; HZI,Helmholtz-Zentrum für Infektionsforschung GmbH, Inhoffenstr. 7,38124 Braunschweig, Germany; TWINCORE, Zentrum für experimentelle und klinische Infektionsforschung GmbH,Feodor-Lynen Str. 7, 30625 Hannover, Germany. (National Academy of Sciences, 2019-09-23)
      cis-Aconitate decarboxylase (CAD, also known as ACOD1 or Irg1) converts cis-aconitate to itaconate and plays central roles in linking innate immunity with metabolism and in the biotechnological production of itaconic acid by Aspergillus terreus We have elucidated the crystal structures of human and murine CADs and compared their enzymological properties to CAD from A. terreus Recombinant CAD is fully active in vitro without a cofactor. Murine CAD has the highest catalytic activity, whereas Aspergillus CAD is best adapted to a more acidic pH. CAD is not homologous to any known decarboxylase and appears to have evolved from prokaryotic enzymes that bind negatively charged substrates. CADs are homodimers, the active center is located in the interface between 2 distinct subdomains, and structural modeling revealed conservation in zebrafish and Aspergillus We identified 8 active-site residues critical for CAD function and rare naturally occurring human mutations in the active site that abolished CAD activity, as well as a variant (Asn152Ser) that increased CAD activity and is common (allele frequency 20%) in African ethnicity. These results open the way for 1) assessing the potential impact of human CAD variants on disease risk at the population level, 2) developing therapeutic interventions to modify CAD activity, and 3) improving CAD efficiency for biotechnological production of itaconic acid.
    • Identifying parameters to improve the reproducibility of transient gene expression in High Five cells.

      Bleckmann, Maren; Schürig, Margitta; Endres, Michelle; Samuels, Anke; Gebauer, Daniela; Konisch, Nadine; van den Heuvel, Joop; HZI,Helmholtz-Zentrum für Infektionsforschung GmbH, Inhoffenstr. 7,38124 Braunschweig, Germany. (PLOS, 2019-01-01)
      Virus-free, transient gene expression (TGE) in High Five cells was recently presented as an efficient protein production method. However, published TGE protocols have not been standardized to a general protocol. Therefore, reproducibility and implementation of the method in other labs remains difficult. The aim of this study is to analyse the parameters determining the reproducibility of the TGE in insect cells. Here, we identified that using linear 40 kDa PEI instead of 25 kDa PEI was one of the most important aspects to improve TGE. Furthermore, DNA amount, DNA:PEI ratio, growth phase of the cells before transfection, passage number, the origin of the High-Five cell isolates and the type of cultivation medium were considered. Interestingly, a correlation of the passage number to the DNA content of single cells (ploidy) and to the transfection efficacy could be shown. The optimal conditions for critical parameters were used to establish a robust TGE method. Finally, we compared the achieved product yields in High Five cells using our improved TGE method with both the baculoviral expression system and TGE in the mammalian HEK293-6E cell line. In conclusion, the presented robust TGE protocol in High Five cells is easy to establish and produces ample amounts of high-quality recombinant protein, bridging the gap in expression level of this method to the well-established mammalian TGE in HEK293 cells as well as to the baculoviral expression vector system (BEVS).
    • ER intrabody-mediated inhibition of interferon α secretion by mouse macrophages and dendritic cells.

      Büssow, Konrad; Themann, Philipp; Luu, Sabine; Pentrowski, Paul; Harting, Claudia; Majewski, Mira; Vollmer, Veith; Köster, Mario; Grashoff, Martina; Zawatzky, Rainer; et al. (Plos, 2019-01-01)
      Interferon α (IFNα) counteracts viral infections by activating various IFNα-stimulated genes (ISGs). These genes encode proteins that block viral transport into the host cell and inhibit viral replication, gene transcription and translation. Due to the existence of 14 different, highly homologous isoforms of mouse IFNα, an IFNα knockout mouse has not yet been established by genetic knockout strategies. An scFv intrabody for holding back IFNα isoforms in the endoplasmic reticulum (ER) and thus counteracting IFNα secretion is reported. The intrabody was constructed from the variable domains of the anti-mouse IFNα rat monoclonal antibody 4EA1 recognizing the 5 isoforms IFNα1, IFNα2, IFNα4, IFNα5, IFNα6. A soluble form of the intrabody had a KD of 39 nM to IFNα4. It could be demonstrated that the anti-IFNα intrabody inhibits clearly recombinant IFNα4 secretion by HEK293T cells. In addition, the secretion of IFNα4 was effectively inhibited in stably transfected intrabody expressing RAW 264.7 macrophages and dendritic D1 cells. Colocalization of the intrabody with IFNα4 and the ER marker calnexin in HEK293T cells indicated complex formation of intrabody and IFNα4 inside the ER. Intracellular binding of intrabody and antigen was confirmed by co-immunoprecipitation. Complexes of endogenous IFNα and intrabody could be visualized in the ER of Poly (I:C) stimulated RAW 264.7 macrophages and D1 dendritic cells. Infection of macrophages and dendritic cells with the vesicular stomatitis virus VSV-AV2 is attenuated by IFNα and IFNβ. The intrabody increased virus proliferation in RAW 264.7 macrophages and D1 dendritic cells under IFNβ-neutralizing conditions. To analyze if all IFNα isoforms are recognized by the intrabody was not in the focus of this study. Provided that binding of the intrabody to all isoforms was confirmed, the establishment of transgenic intrabody mice would be promising for studying the function of IFNα during viral infection and autoimmune diseases.
    • Investigations on the mode of action of gephyronic acid, an inhibitor of eukaryotic protein translation from myxobacteria.

      Muthukumar, Yazh; Münkemer, Johanna; Mathieu, Daniel; Richter, Christian; Schwalbe, Harald; Steinmetz, Heinrich; Kessler, Wolfgang; Reichelt, Joachim; Beutling, Ulrike; Frank, Ronald; et al. (PLOS, 2018-01-01)
      The identification of inhibitors of eukaryotic protein biosynthesis, which are targeting single translation factors, is highly demanded. Here we report on a small molecule inhibitor, gephyronic acid, isolated from the myxobacterium Archangium gephyra that inhibits growth of transformed mammalian cell lines in the nM range. In direct comparison, primary human fibroblasts were shown to be less sensitive to toxic effects of gephyronic acid than cancer-derived cells. Gephyronic acid is targeting the protein translation system. Experiments with IRES dual luciferase reporter assays identified it as an inhibitor of the translation initiation. DARTs approaches, co-localization studies and pull-down assays indicate that the binding partner could be the eukaryotic initiation factor 2 subunit alpha (eIF2α). Gephyronic acid seems to have a different mode of action than the structurally related polyketides tedanolide, myriaporone, and pederin and is a valuable tool for investigating the eukaryotic translation system. Because cancer derived cells were found to be especially sensitive, gephyronic acid could potentially find use as a drug candidate.
    • Bithionol Potently Inhibits Human Soluble Adenylyl Cyclase through Binding to the Allosteric Activator Site.

      Kleinboelting, Silke; Ramos-Espiritu, Lavoisier; Buck, Hannes; Colis, Laureen; van den Heuvel, Joop; Glickman, J Fraser; Levin, Lonny R; Buck, Jochen; Steegborn, Clemens; Helmholtz Zentrum für Infektionsforschung GmbH, Inhoffenstr. 7, 38124 Braunschweig, Germany. (2016-04-29)
      The signaling molecule cAMP regulates functions ranging from bacterial transcription to mammalian memory. In mammals, cAMP is synthesized by nine transmembrane adenylyl cyclases (ACs) and one soluble AC (sAC). Despite similarities in their catalytic domains, these ACs differ in regulation. Transmembrane ACs respond to G proteins, whereas sAC is uniquely activated by bicarbonate. Via bicarbonate regulation, sAC acts as a physiological sensor for pH/bicarbonate/CO2, and it has been implicated as a therapeutic target, e.g. for diabetes, glaucoma, and a male contraceptive. Here we identify the bisphenols bithionol and hexachlorophene as potent, sAC-specific inhibitors. Inhibition appears mostly non-competitive with the substrate ATP, indicating that they act via an allosteric site. To analyze the interaction details, we solved a crystal structure of an sAC·bithionol complex. The structure reveals that the compounds are selective for sAC because they bind to the sAC-specific, allosteric binding site for the physiological activator bicarbonate. Structural comparison of the bithionol complex with apo-sAC and other sAC·ligand complexes along with mutagenesis experiments reveals an allosteric mechanism of inhibition; the compound induces rearrangements of substrate binding residues and of Arg(176), a trigger between the active site and allosteric site. Our results thus provide 1) novel insights into the communication between allosteric regulatory and active sites, 2) a novel mechanism for sAC inhibition, and 3) pharmacological compounds targeting this allosteric site and utilizing this mode of inhibition. These studies provide support for the future development of sAC-modulating drugs.
    • Fast plasmid based protein expression analysis in insect cells using an automated SplitGFP screen.

      Bleckmann, Maren; Schmelz, Stefan; Schinkowski, Christian; Scrima, Andrea; van den Heuvel, Joop; Helmholtz Centre for infection research, Inhoffenstr. 7, 38124 Braunschweig, Germany. (2016-02-23)
      Recombinant protein expression often presents a bottleneck for the production of proteins for use in many areas of animal-cell biotechnology. Difficult-to-express proteins require the generation of numerous expression constructs, where popular prokaryotic screening systems often fail to identify expression of multi domain or full-length protein constructs. Post-translational modified mammalian proteins require an alternative host system such as insect cells using the Baculovirus Expression Vector System (BEVS). Unfortunately this is time-, labor- and cost-intensive. It is clearly desirable to find an automated and miniaturized fast multi-sample screening method for protein expression in such systems. With this in mind, in this paper a high-throughput initial expression screening method is described using an automated Microcultivation system in conjunction with fast plasmid based transient transfection in insect cells for the efficient generation of protein constructs. The applicability of the system is demonstrated for the difficult to express Nucleotide-binding Oligomerization Domain-containing protein 2 (NOD2). To enable detection of proper protein expression the rather weak plasmid based expression has been improved by a sensitive inline detection system. Here we present the functionality and application of the sensitive SplitGFP (split green fluorescent protein) detection system in insect cells. The successful expression of constructs is monitored by direct measurement of the fluorescence in the BioLector Microcultivation system. Additionally, we show that the results obtained with our plasmid based SplitGFP protein expression screen correlate directly to the level of soluble protein produced in BEVS. In conclusion our automated SplitGFP screen outlines a sensitive, fast and reliable method reducing the time and costs required for identifying the optimal expression construct prior to large scale protein production in baculovirus infected insect cells. This article is protected by copyright. All rights reserved.
    • Discovery of LRE1 as a specific and allosteric inhibitor of soluble adenylyl cyclase.

      Ramos-Espiritu, Lavoisier; Kleinboelting, Silke; Navarrete, Felipe A; Alvau, Antonio; Visconti, Pablo E; Valsecchi, Federica; Starkov, Anatoly; Manfredi, Giovanni; Buck, Hannes; Adura, Carolina; et al. (2016)
      The prototypical second messenger cAMP regulates a wide variety of physiological processes. It can simultaneously mediate diverse functions by acting locally in independently regulated microdomains. In mammalian cells, two types of adenylyl cyclase generate cAMP: G-protein-regulated transmembrane adenylyl cyclases and bicarbonate-, calcium- and ATP-regulated soluble adenylyl cyclase (sAC). Because each type of cyclase regulates distinct microdomains, methods to distinguish between them are needed to understand cAMP signaling. We developed a mass-spectrometry-based adenylyl cyclase assay, which we used to identify a new sAC-specific inhibitor, LRE1. LRE1 bound to the bicarbonate activator binding site and inhibited sAC via a unique allosteric mechanism. LRE1 prevented sAC-dependent processes in cellular and physiological systems, and it will facilitate exploration of the therapeutic potential of sAC inhibition.
    • Identification of Essential Genetic Baculoviral Elements for Recombinant Protein Expression by Transactivation in Sf21 Insect Cells.

      Bleckmann, Maren; Schürig, Margitta; Chen, Fang-Fang; Yen, Zen-Zen; Lindemann, Nils; Meyer, Steffen; Spehr, Johannes; van den Heuvel, Joop; Helmholtz Centre for infection research (HZI), Inhoffenstraße 7, 38124 Braunschweig, Germany. (2016)
      The Baculovirus Expression Vector System (BEVS) is widely used to produce high amounts of recombinant proteins. Nevertheless, generating recombinant baculovirus in high quality is rather time-consuming and labor-intensive. Alternatively, virus-free expression in insect cells did not achieve similar expression levels for most proteins so far. The transactivation method is a promising approach for protein expression in Sf21 cells. It combines advantages of BEVS and plasmid-based expression by activating strong virus-dependent promoters on a transfected plasmid by baculoviral coinfection. Here, we identified expression elements required for transactivation. Therefore, we designed several vectors comprising different viral promoters or promoter combinations and tested them for eGFP expression using the automated BioLector microcultivation system. Remarkably, only the combination of the very late promoter p10 together with the homologous region 5 (hr5) could boost expression during transactivation. Other elements, like p10 alone or the late viral promoter polH, did not respond to transactivation. A new combination of hr5 and p10 with the strongest immediate early OpMNPV viral promoter OpIE2 improved the yield of eGFP by ~25% in comparison to the previous applied hr5-IE1-p10 expression cassette. Furthermore, we observed a strong influence of the transcription termination sequence and vector backbone on the level of expression. Finally, the expression levels for transactivation, BEVS and solely plasmid-based expression were compared for the marker protein eGFP, underlining the potential of transactivation for fast recombinant protein expression in Sf21 cells. In conclusion, essential elements for transactivation could be identified. The optimal elements were applied to generate an improved vector applicable in virus-free plasmid-based expression, transactivation and BEVS.
    • Assessing stability and assembly of the hepatitis B surface antigen into virus-like particles during down-stream processing.

      Zahid, Maria; Lünsdorf, Heinrich; Rinas, Ursula; Helmholtz Centre for infection research, Inhoffenstr. 7, 38124 Braunschweig, Germany. (2015-07-17)
      The hepatitis B surface antigen (HBsAg) is a recombinant protein-based vaccine being able to form virus-like particles (VLPs). HBsAg is mainly produced using yeast-based expression systems, however, recent results strongly suggest that VLPs are not formed within the yeast cells during the cultivation but are formed in a gradual manner during the following down-stream procedures. VLPs are also not detectable during the first down-stream steps including mechanical and EDTA/detergent-assisted cell destruction. Moreover, VLPs are not detectable in the cell lysate treated with polyethylene glycol and colloidal silica. The first VLP resembling structures appear after elution of HBsAg from colloidal silica to which it binds through hydrophobic interaction. These first VLP resembling structures are non-symmetrical as well as heterodisperse and exhibit a high tendency toward cluster formation presumably because of surface exposed hydrophobic patches. More symmetrical and monodisperse VLPs appear after the following ion-exchange and size-exclusion chromatography most likely as the result of buffer changes during these purification steps (toward more neutral pH and less salt). Final treatment of the VLPs with the denaturant KSCN at moderate concentrations with following KSCN removal by dialysis does not cause unfolding and VLP disassembly but results in a re- and fine-structuring of the VLP surface topology.
    • Stable mammalian producer cell lines for structural biology.

      Büssow, Konrad; Helmholtz Centre for Infection Research, Structure and Function of Proteins, Inhoffenstr. 7, 38124 Braunschweig, Germany. (2015-03-21)
      The mammalian cell lines HEK293 and CHO have become important expression hosts in structural biology. Generating stable mammalian cell lines remains essential for studying the function and structure of recombinant proteins, despite the emergence of highly efficient transient transfection protocols. Production with stable cell lines can be scaled up easily and high volumetric product yield can be achieved. Protein structure reports of the past two years that used stable cell lines were surveyed for this review. Well-established techniques and novel approaches for generating stable cell lines and stable cell pools are presented, including cell sorting, site-specific recombination, transposons, the Lentivirus system and phage integrases. Host cell line optimization by endoglycosidase overexpression and sequence-specific genome engineering is highlighted.
    • Cryo-EM structure of Hepatitis C virus IRES bound to the human ribosome at 3.9-Å resolution.

      Quade, Nick; Boehringer, Daniel; Leibundgut, Marc; van den Heuvel, Joop; Ban, Nenad; Helmholtz Centre for Infection Research, Inhoffenstraße 7, 38124 Braunschweig, Germany. (2015)
      Hepatitis C virus (HCV), a widespread human pathogen, is dependent on a highly structured 5'-untranslated region of its mRNA, referred to as internal ribosome entry site (IRES), for the translation of all of its proteins. The HCV IRES initiates translation by directly binding to the small ribosomal subunit (40S), circumventing the need for many eukaryotic translation initiation factors required for mRNA scanning. Here we present the cryo-EM structure of the human 40S ribosomal subunit in complex with the HCV IRES at 3.9 Å resolution, determined by focused refinement of an 80S ribosome-HCV IRES complex. The structure reveals the molecular details of the interactions between the IRES and the 40S, showing that expansion segment 7 (ES7) of the 18S rRNA acts as a central anchor point for the HCV IRES. The structural data rationalizes previous biochemical and genetic evidence regarding the initiation mechanism of the HCV and other related IRESs.
    • Specific in vivo knockdown of protein function by intrabodies.

      Marschall, Andrea L J; Dübel, Stefan; Böldicke, Thomas; Helmholtz Centre for infection researchz, Inhoffenstr. 7, 38124 Braunschweig. (2015)
      Intracellular antibodies (intrabodies) are recombinant antibody fragments that bind to target proteins expressed inside of the same living cell producing the antibodies. The molecules are commonly used to study the function of the target proteins (i.e., their antigens). The intrabody technology is an attractive alternative to the generation of gene-targeted knockout animals, and complements knockdown techniques such as RNAi, miRNA and small molecule inhibitors, by-passing various limitations and disadvantages of these methods. The advantages of intrabodies include very high specificity for the target, the possibility to knock down several protein isoforms by one intrabody and targeting of specific splice variants or even post-translational modifications. Different types of intrabodies must be designed to target proteins at different locations, typically either in the cytoplasm, in the nucleus or in the endoplasmic reticulum (ER). Most straightforward is the use of intrabodies retained in the ER (ER intrabodies) to knock down the function of proteins passing the ER, which disturbs the function of members of the membrane or plasma proteomes. More effort is needed to functionally knock down cytoplasmic or nuclear proteins because in this case antibodies need to provide an inhibitory effect and must be able to fold in the reducing milieu of the cytoplasm. In this review, we present a broad overview of intrabody technology, as well as applications both of ER and cytoplasmic intrabodies, which have yielded valuable insights in the biology of many targets relevant for drug development, including α-synuclein, TAU, BCR-ABL, ErbB-2, EGFR, HIV gp120, CCR5, IL-2, IL-6, β-amyloid protein and p75NTR. Strategies for the generation of intrabodies and various designs of their applications are also reviewed.
    • Genomic Analysis and Isolation of RNA Polymerase II Dependent Promoters from Spodoptera frugiperda.

      Bleckmann, Maren; Fritz, Markus H-Y; Bhuju, Sabin; Jarek, Michael; Schürig, Margitta; Geffers, Robert; Benes, Vladimir; Besir, Hüseyin; van den Heuvel, Joop; Helmholtz Centre for infection research, Inhoffenstr. 7, 38124 Braunschweig, Germany. (2015)
      The Baculoviral Expression Vector System (BEVS) is the most commonly used method for high expression of recombinant protein in insect cells. Nevertheless, expression of some target proteins--especially those entering the secretory pathway--provides a severe challenge for the baculovirus infected insect cells, due to the reorganisation of intracellular compounds upon viral infection. Therefore, alternative strategies for recombinant protein production in insect cells like transient plasmid-based expression or stable expression cell lines are becoming more popular. However, the major bottleneck of these systems is the lack of strong endogenous polymerase II dependent promoters, as the strong baculoviral p10 and polH promoters used in BEVS are only functional in presence of the viral transcription machinery during the late phase of infection. In this work we present a draft genome and a transcriptome analysis of Sf21 cells for the identification of the first known endogenous Spodoptera frugiperda promoters. Therefore, putative promoter sequences were identified and selected because of high mRNA level or in analogy to other strong promoters in other eukaryotic organism. The chosen endogenous Sf21 promoters were compared to early viral promoters for their efficiency to trigger eGFP expression using transient plasmid based transfection in a BioLector Microfermentation system. Furthermore, promoter activity was not only shown in Sf21 cells but also in Hi5 cells. The novel endogenous Sf21 promoters were ranked according to their activity and expand the small pool of available promoters for stable insect cell line development and transient plasmid expression in insect cells. The best promoter was used to improve plasmid based transient transfection in insect cells substantially.
    • Smart sustainable bottle (SSB) system for E. coli based recombinant protein production

      Li, Zhaopeng; Carstensen, Bettina; Rinas, Ursula (2014-11-05)
      Abstract Background Recombinant proteins are usually required in laboratories interested in the protein but not in the production process itself. Thus, technical equipment which is easy to handle and straight forward protein production procedures are of great benefit to those laboratories. Companies selling single use cultivation bags and bioreactors are trying to satisfy at least part of these needs. However, single-use systems can contribute to major costs which might be acceptable when “good manufacturing practices” are required but not acceptable for most laboratories facing tight funding. Results The assembly and application of a simple self-made “smart sustainable bottle” (SSB) system for E. coli based protein production is presented. The core of the SSB system is a 2-L glass bottle which is operated at constant temperature, air flow, and stirrer speed without measurement and control of pH and dissolved oxygen. Oxygen transfer capacities are in the range as in conventional bioreactors operated at intermediate aeration rates and by far exceed those found in conventional shaking flasks and disposable bioreactors. The SSB system was applied for the production of various recombinant proteins using T7-based expression systems and a defined autoinduction medium. The production performance regarding amount and solubility of proteins with robust and delicate properties was as good as in state-of-the-art stirred tank commercial bioreactors. Conclusions The SSB system represents a low cost protein production device applicable for easy, effective, and reproducible recombinant protein production.
    • Expression, purification, crystallization and preliminary X-ray diffraction analysis of a mammalian type 10 adenylyl cyclase.

      Kleinboelting, Silke; van den Heuvel, Joop; Kambach, Christian; Weyand, Michael; Leipelt, Martina; Steegborn, Clemens (2014-04)
      The second messenger cAMP is synthesized in mammals by ten differently regulated adenylyl cyclases (AC1-10). These ACs are grouped into nucleotidyl cyclase class III based on homologies in their catalytic domains. The catalytic domain of AC10 is unique, however, in being activated through direct interaction with calcium and bicarbonate. Here, the production, crystallization and X-ray diffraction analysis of the catalytic domain of human AC10 are described as a basis for structural studies of regulator binding sites and mechanisms. The recombinant protein had high specific AC activity, and crystals of AC10 in space group P63 diffracted to ∼2.0 Å resolution on a synchrotron beamline. A complete diffraction data set revealed unit-cell parameters a = b = 99.65, c = 98.04 Å, indicating one AC10 catalytic domain per asymmetric unit, and confirmed that the obtained crystals are suitable for structure solution and mechanistic studies.
    • Decrease of UPR- and ERAD-related proteins in Pichia pastoris during methanol-induced secretory insulin precursor production in controlled fed-batch cultures.

      Vanz, Ana Letícia; Nimtz, Manfred; Rinas, Ursula (2014)
      Pichia pastoris is a popular yeast preferably employed for secretory protein production. Secretion is not always efficient and endoplasmic retention of proteins with aberrant folding properties, or when produced at exaggerated rates, can occur. In these cases production usually leads to an unfolded protein response (UPR) and the induction of the endoplasmic reticulum associated degradation (ERAD). P. pastoris is nowadays also an established host for secretory insulin precursor (IP) production, though little is known about the impact of IP production on the host cell physiology, in particular under industrially relevant production conditions. Here, we evaluate the cellular response to aox1 promoter-controlled, secretory IP production in controlled fed-batch processes using a proteome profiling approach.
    • The metabolic potential of Escherichia coli BL21 in defined and rich medium.

      Li, Zhaopeng; Nimtz, Manfred; Rinas, Ursula (2014)
      The proteome reflects the available cellular machinery to deal with nutrients and environmental challenges. The most common E. coli strain BL21 growing in different, commonly employed media was evaluated using a detailed quantitative proteome analysis.
    • Purification of hepatitis B surface antigen virus-like particles from recombinant Pichia pastoris and in vivo analysis of their immunogenic properties.

      Gurramkonda, Chandrasekhar; Zahid, Maria; Nemani, Satish Kumar; Adnan, Ahmad; Gudi, Satheesh Kumar; Khanna, Navin; Ebensen, Thomas; Lünsdorf, Heinrich; Guzmán, Carlos A; Rinas, Ursula; et al. (2013-12-01)
      Following earlier studies on high-level intracellular production of hepatitis B surface antigen (HBsAg) using recombinant Pichia pastoris, we present here in detail an enhanced method for the purification of recombinant HBsAg virus-like particles (VLPs). We have screened various detergents for their ability to promote the solubilization of recombinant intracellular HBsAg. In addition, we have analyzed the effect of cell disruption and extraction regarding their impact on the release of HBsAg. Our results show that introduction of the mild nonionic detergent Tween 20 in the initial process of cell lysis at ∼600bars by high pressure homogenization leads to the best results. The subsequent purification steps involved polyethylene glycol precipitation of host cell contaminants, hydrophobic adsorption of HBsAg to colloidal silica followed by ion-exchange chromatography and either isopycnic density ultracentrifugation or size exclusion chromatography for the recovery of the VLPs. After final KSCN treatment and dialysis, a total yield of ∼3% with a purity of >99% was reached. The pure protein was characterized by electron microscopy, showing the presence of uniform VLPs which are the pre-requisite for immunogenicity. The intramuscular co-administration of HBsAg VLPs, with either alum or a PEGylated-derivative of the toll-like receptor 2/6 agonist MALP-2, to mice resulted in the elicitation of significantly higher HBsAg-specific IgG titers as well as a stronger cellular immune response compared to mice vaccinated with a gold standard vaccine (Engerix™). These results show that P. pastoris derived HBsAg VLPs exhibit a high potential as a superior biosimilar vaccine against hepatitis B.
    • Folding and dimerization kinetics of bone morphogenetic protein-2, a member of the transforming growth factor-β family.

      Vallejo, Luis F; Rinas, Ursula; Helmholtz Centre for Infection Research, Braunschweig, Germany. (2013-01)
      The kinetics of folding and dimerization of bone morphogenetic protein-2 (BMP-2), a disulfide-connected, homodimeric cystine-knot protein and a member of the transforming growth factor-β superfamily, was analyzed under a variety of different conditions. Refolding and dimerization of BMP-2 were extremely slow under all conditions studied, and could be described by consecutive first-order reactions involving at least one long-lived intermediate. The rate constants vary from ~ 0.2 × 10(-5) to ~ 3.5 × 10(-5) s(-1), and were strongly dependent on temperature, redox conditions, and the presence of stabilizing or destabilizing ions. In particular, the combined impact of ionic strength and redox conditions on the rates indicates that electrostatic interactions control thiol-disulfide exchange reactions on the path from the unfolded and reduced monomers to the disulfide-connected growth factor in a rate-determining way.
    • High level transient production of recombinant antibodies and antibody fusion proteins in HEK293 cells.

      Jäger, Volker; Büssow, Konrad; Wagner, Andreas; Weber, Susanne; Hust, Michael; Frenzel, André; Schirrmann, Thomas; Helmholtz Centre for infection research, Inhoffenstr. 7, 38124 Braunschweig, Germany. (2013)
      The demand of monospecific high affinity binding reagents, particularly monoclonal antibodies, has been steadily increasing over the last years. Enhanced throughput of antibody generation has been addressed by optimizing in vitro selection using phage display which moved the major bottleneck to the production and purification of recombinant antibodies in an end-user friendly format. Single chain (sc)Fv antibody fragments require additional tags for detection and are not as suitable as immunoglobulins (Ig)G in many immunoassays. In contrast, the bivalent scFv-Fc antibody format shares many properties with IgG and has a very high application compatibility.