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

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

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

Screening and Production of Recombinant Human Proteins: Protein Production in E. coli

In Chapter 3 , we described the Structural Genomics Consortium (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 structural studies (e.g., crystallization or cryo-EM 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

Structure of the C-Terminal Domain of the Multifunctional ICP27 Protein from Herpes Simplex Virus 1

Herpesviruses are nuclear-replicating viruses that have successfully evolved to evade the immune system of humans, establishing lifelong infections. ICP27 from herpes simplex virus is a multifunctional regulatory protein that is functionally conserved in all known human herpesviruses. It has the potential to interact with an array of cellular proteins, as well as intronless viral RNAs. ICP27 plays an essential role in viral transcription, nuclear export of intronless RNAs, translation of viral transcripts, and virion host shutoff function. It has also been implicated in several signaling pathways and the prevention of apoptosis. Although much is known about its central role in viral replication and infection, very little is known about the structure and mechanistic properties of ICP27 and its homologs. We present the first crystal structure of ICP27 C-terminal domain at a resolution of 2.0 Å. The structure reveals the C-terminal half of ICP27 to have a novel fold consisting of α-helices and long loops, along with a unique CHCC-type of zinc-binding motif. The two termini of this domain extend from the central core and hint to possibilities of making interactions. ICP27 essential domain is capable of forming self-dimers as seen in the structure, which is confirmed by analytical ultracentrifugation study. Preliminary in vitro phosphorylation assays reveal that this domain may be regulated by cellular kinases. IMPORTANCE ICP27 is a key regulatory protein of the herpes simplex virus and has functional homologs in all known human herpesviruses. Understanding the structure of this protein is a step ahead in deciphering the mechanism by which the virus thrives. In this study, we present the first structure of the C-terminal domain of ICP27 and describe its novel features. We critically analyze the structure and compare our results to the information available form earlier studies. This structure can act as a guide in future experimental designs and can add to a better understanding of mechanism of ICP27, as well as that of its homologs