A high-throughput immobilized bead screen for stable proteins and multi-protein complexes

We describe an in vitro colony screen to identify Escherichia coli expressing soluble proteins and stable, assembled multiprotein complexes. Proteins with an N-terminal 6His tag and C-terminal green fluorescent protein (GFP) S11 tag are fluorescently labeled in cells by complementation with a coexpressed GFP 1–10 fragment. After partial colony lysis, the fluorescent soluble proteins or complexes diffuse through a supporting filtration membrane and are captured on Talon® resin metal affinity beads immobilized in agarose. Images of the fluorescent colonies convey total expression and the level of fluorescence bound to the beads indicates how much protein is soluble. Both pieces of information can be used together when selecting clones. After the assay, colonies can be picked and propagated, eliminating the need to make replica plates. We used the method to screen a DNA fragment library of the human protein p85 and preferentially obtained clones expressing the full-length ‘breakpoint cluster region-homology' and NSH2 domains. The assay also distinguished clones expressing stable multi-protein complexes from those that are unstable due to missing subunits. Clones expressing stable, intact heterotrimeric E.coli YheNML complexes were readily identified in libraries dominated by complexes of YheML missing the N subunit

Experimental mapping of soluble protein domains using a hierarchical approach

Exploring the function and 3D space of large multidomain protein targets often requires sophisticated experimentation to obtain the targets in a form suitable for structure determination. Screening methods capable of selecting well-expressed, soluble fragments from DNA libraries exist, but require the use of automation to maximize chances of picking a few good candidates. Here, we describe the use of an insertion dihydrofolate reductase (DHFR) vector to select in-frame fragments and a split-GFP assay technology to filter-out constructs that express insoluble protein fragments. With the incorporation of an IPCR step to create high density, focused sublibraries of fragments, this cost-effective method can be performed manually with no a priori knowledge of domain boundaries while permitting single amino acid resolution boundary mapping. We used it on the well-characterized p85α subunit of the phosphoinositide-3-kinase to demonstrate the robustness and efficiency of our methodology. We then successfully tested it onto the polyketide synthase PpsC from Mycobacterium tuberculosis, a potential drug target involved in the biosynthesis of complex lipids in the cell envelope. X-ray quality crystals from the acyl-transferase (AT), dehydratase (DH) and enoyl-reductase (ER) domains have been obtained

Identification of soluble protein fragments by gene fragmentation and genetic selection

We describe a new method, which identifies protein fragments for soluble expression in Escherichia coli from a randomly fragmented gene library. Inhibition of E. coli dihydrofolate reductase (DHFR) by trimethoprim (TMP) prevents growth, but this can be relieved by murine DHFR (mDHFR). Bacterial strains expressing mDHFR fusions with the soluble proteins green fluroscent protein (GFP) or EphB2 (SAM domain) displayed markedly increased growth rates with TMP compared to strains expressing insoluble EphB2 (TK domain) or ketosteroid isomerase (KSI). Therefore, mDHFR is affected by the solubility of fusion partners and can act as a reporter of soluble protein expression. Random fragment libraries of the transcription factor Fli1 were generated by deoxyuridine incorporation and endonuclease V cleavage. The fragments were cloned upstream of mDHFR and TMP resistant clones expressing soluble protein were identified. These were found to cluster around the DNA binding ETS domain. A selected Fli1 fragment was expressed independently of mDHFR and was judged to be correctly folded by various biophysical methods including NMR. Soluble fragments of the cell-surface receptor Pecam1 were also identified. This genetic selection method was shown to generate expression clones useful for both structural studies and antibody generation and does not require a priori knowledge of domain architecture

HF-EPR, Raman, UV/VIS Light Spectroscopic, and DFT Studies of the Ribonucleotide Reductase R2 Tyrosyl Radical from Epstein-Barr Virus

Epstein-Barr virus (EBV) belongs to the gamma subfamily of herpes viruses, among the most common pathogenic viruses in humans worldwide. The viral ribonucleotide reductase small subunit (RNR R2) is involved in the biosynthesis of nucleotides, the DNA precursors necessary for viral replication, and is an important drug target for EBV. RNR R2 generates a stable tyrosyl radical required for enzymatic turnover. Here, the electronic and magnetic properties of the tyrosyl radical in EBV R2 have been determined by X-band and high-field/high-frequency electron paramagnetic resonance (EPR) spectroscopy recorded at cryogenic temperatures. The radical exhibits an unusually low g1-tensor component at 2.0080, indicative of a positive charge in the vicinity of the radical. Consistent with these EPR results a relatively high C-O stretching frequency associated with the phenoxyl radical (at 1508 cm−1) is observed with resonance Raman spectroscopy. In contrast to mouse R2, EBV R2 does not show a deuterium shift in the resonance Raman spectra. Thus, the presence of a water molecule as a hydrogen bond donor moiety could not be identified unequivocally. Theoretical simulations showed that a water molecule placed at a distance of 2.6 Å from the tyrosyl-oxygen does not result in a detectable deuterium shift in the calculated Raman spectra. UV/VIS light spectroscopic studies with metal chelators and tyrosyl radical scavengers are consistent with a more accessible dimetal binding/radical site and a lower affinity for Fe2+ in EBV R2 than in Escherichia coli R2. Comparison with previous studies of RNR R2s from mouse, bacteria, and herpes viruses, demonstrates that finely tuned electronic properties of the radical exist within the same RNR R2 Ia class

Novel Technologies for Recombinant Protein Overexpression in Escherichia coli

The use of recombinant protein is a cornerstone in many structural and functional studies. The enteric bacterium Escherichia Coli is the most commonly used organism for producing recombinant proteins. E. coli has several advantages over other expression hosts, but also one major disadvantage - the protein of interest does not always adopt its native conformation. Instead the protein might form large insoluble aggregates, inclusion bodies, within the cell. In particular, the heterologous overexpression of eukaryotic and membrane proteins are troublesome. In this thesis, methods are described that can be used to increase the likelihood of overexpressing eukaryotic proteins as well as membrane proteins. In particular, a novel method is described that can distinguish between bacterial colonies expressing soluble proteins from those expressing inclusion bodies. The method utilizes the fact that inclusion bodies are of a considerable size and can be removed by filtration. Using this screening method in combination with methods that alter the physical properties of proteins, we have shown that the likelihood of overexpression in E. coli can be dramatically increased

Talet om invandrarkvinnan i svensk dagspress

Medias makt att påverka individers sätt att tolka verkligheten är stor. Alltså blir betydelsen för hur man väljer att skriva någonting viktigt då det påverkar den sociala praktiken, i fråga om makt, inflytande för individer och grupper. Vi har i denna uppsats lagt fokus på svensk nyhetsmedias framställning av invandrarkvinnan. Vårt syfte med uppsatsen var att undersöka och analysera diskursen kring invandrarkvinnan i svensk dags- samt kvällspress utifrån frågeställningarna; Hur skildras den invandrade kvinnan i svensk dags- samt kvällspress? och Förekommer stereotyper kring invandrarkvinnan och i så fall hur ser de ut? Det finns ingen tidigare forskning med samma syfte, dock förekommer det forskning kring hur media skildrar invandrare och flyktingar. Den tidigare forskningen pekar på medias roll i skapandet av De Andra i syfte att skapa en svensk identitet. Vi har genomfört en kritisk diskursanalys med utgångspunkt i Faircloughs Critical Discourse Analysis. Uppsatsens teoretiska utgångspunkter har varit socialkonstruktivism och genusteori. Empirin är baserad på 63 artiklar hämtade från Svenska Dagbladet, Dagens Nyheter, Expressen och Aftonbladet, publicerade under åren 2005 och 2006. De fyra teman som var tydliga i artikelmaterialet är: konstruktionen av de andra, heder, religion & kultur samt integration. Våra resultat visar på ett likartat skildrande av den invandrade kvinnan som ett offer för olika strukturer. Dels för samhälliga strukturer samt för kulturella och religiösa strukturer. Vårt artikelmaterial påvisar även en motdiskurs, om än en svag sådan, i vilken invandrarkvinnans etniska och kulturella bakgrund framställs som någonting positivt

Medium-throughput production of recombinant human proteins: protein production in E. coli.

In Chapter 4 we described the SGC process for generating multiple constructs of truncated versions of each protein using LIC. In this chapter we provide a step-by-step procedure of our E. coli system for test expressing intracellular (soluble) proteins in a 96-well format that enables us to identify which proteins or truncated versions are expressed in a soluble and stable form suitable for structural studies. In addition, we detail the process for scaling up cultures for large-scale protein purification. This level of production is required to obtain sufficient quantities (i.e., milligram amounts) of protein for further characterization and/or crystallization experiments. Our standard process is purification by immobilized metal affinity chromatography (IMAC) using nickel resin followed by size exclusion chromatography (SEC), with additional procedures arising from the complexity of the protein itself

Medium-throughput production of recombinant human proteins: Protein production in E. Coli

In Chapter 4 we described the SGC process for generating multiple constructs of truncated versions of each protein using LIC. In this chapter we provide a step-by-step procedure of our E. coli system for test expressing intracellular (soluble) proteins in a 96-well format that enables us to identify which proteins or truncated versions are expressed in a soluble and stable form suitable for structural studies. In addition, we detail the process for scaling up cultures for large-scale protein purification. This level of production is required to obtain sufficient quantities (i.e., milligram amounts) of protein for further characterization and/or crystallization experiments. Our standard process is purification by immobilized metal affinity chromatography (IMAC) using nickel resin followed by size exclusion chromatography (SEC), with additional procedures arising from the complexity of the protein itself. © 2014 Springer Science+Business Media, LLC

The transient complex of poplar plastocyanin with cytochrome f: effects of ionic strength and pH

10 páginas, 7 figurasThe orientation of poplar plastocyanin in the complex with turnip cytochrome f has been determined by rigid-body calculations using restraints from paramagnetic NMR measurements. The results show that poplar plastocyanin interacts with cytochrome f with the hydrophobic patch of plastocyanin close to the heme region on cytochrome f and via electrostatic interactions between the charged patches on both proteins. Plastocyanin is tilted relative to the orientation reported for spinach plastocyanin, resulting in a longer distance between iron and copper (13.9 A). With increasing ionic strength, from 0.01 to 0.11 M, all observed chemical-shift changes decrease uniformly, supporting the idea that electrostatic forces contribute to complex formation. There is no indication for a rearrangement of the transient complex in this ionic strength range, contrary to what had been proposed earlier on the basis of kinetic data. By decreasing the pH from pH 7.7 to pH 5.5, the complex is destabilized. This may be attributed to the protonation of the conserved acidic patches or the copper ligand His87 in poplar plastocyanin, which are shown to have similar pK(a) values. The results are interpreted in a two-step model for complex formation.CL and IDM acknowledge financial support of the Program Human Potential and Mobility of Researchers of the European Commission (contract no. HPRN-CT-1999-00095, ‘Transient Network’) and the Spanish Ministry of Education, Culture and Sport (AP2000-2937). MU is supported financially by the Netherlands Organisation for Scientific Research (grant 700.52.425).Peer reviewe