Protein Analysis and Purification

Characterizing Compound Binding in Cell-Free Systems

Posted on by Gary Kobs

Dioxins (e.g., 2,3,7,8-Tetrachlorodibenzo-p-dioxin, TCDD) and related compounds (DRCs) are persistent environmental pollutants that gradually accumulate through the food chain, mainly in the fatty tissues of animals. Dioxins are highly toxic and can cause reproductive and developmental problems, damage the immune system, interfere with hormones and also cause cancer. This broad range of toxic and biological effects of DRCs is mostly mediated by the aryl hydrocarbon receptor (AHR).

In animal cells, DRCs bind to AHR in the cytoplasm and then translocate into the nucleus, where they affect the transcription of multiple target genes, including xenobiotic-metabolizing enzymes, such as CYP1A isozymes. AHR is also involved in immune system maintenance, protein degradation and cell proliferation.

The jungle crow (Corvus macrorhynchos) has been considered a suitable indicator for monitoring environmental chemicals such as DRCs. While mammals only have one AHR form, avian species have multiple AHR isoforms such as AHR1 and AHR2. To unveil the functional diversity of multiple avian AHR isoforms in terms of their contribution to responses to DRCs a recent study by Kim et al. investigated the molecular and functional characteristics of jungle crow AHR isoforms, cAHR1 and jcAHR2 (1).

cAHR1 and jcAHR2 proteins were synthesized using AHR proteins were synthesized using the TnT Quick-Coupled Reticulocyte Lysate System  to examine whether these jcAHRs have the potential to bind to TCDD. TCDD-binding affinity of the in vitro-expressed jcAHR protein was analyzed using the velocity sedimentation assay with a sucrose gradient.

The results demonstrate that both jcAHR1and jcAHR2 are capable of binding to TCDD.

Reference
Kim, E-Y (2019) The aryl hydrocarbon receptor 2 potentially mediates cytochrome P450 1A induction in the jungle crow (Corvus macrorhynchos). Ecotoxicology and Environmental Safety 171. 99–111

Mutation Analysis Using HaloTag Fusion Proteins

Posted on by Gary Kobs

In a recent reference, Kinoshita and colleagues characterized the phosphorylation dynamics of MEK1 in human cells by using the phosphate affinity electrophoresis technique, Phos-tag sodium dodecyl sulfate–polyacrylamide gel electrophoresis (Phos-tag SDS-PAGE; 1). They found that multiple variants of MEK1 with diferent phosphorylation states are constitutively present in typical human cells.

To investigate the relationships between kinase activity and drug efficacy researchers from the same laboratory group conducted phosphorylation profling of various MEK1 mutants by using Phos-tag SDS- PAGE (2).

They introduced mutations in of the MEK-1 coding gene that are associated with spontaneous melanoma, lung cancer, gastric cancer, colon cancer and ovarian cancer were introduced into Flexi HaloTag clone pFN21AE0668, which is suitable for expression of N-terminal HaloTag-fused MEK1 in mammalian cells. Continue reading “Mutation Analysis Using HaloTag Fusion Proteins”

A BiT or BRET, Which is Better?

Posted on by Joliene Lindholm

Now that Promega is expanding its offerings of options for examining live-cell protein interactions or quantitation at endogenous protein expression levels, we in Technical Services are getting the question about which option is better. The answer is, as with many assays… it depends! First let’s talk about what are the NanoBiT and NanoBRET technologies, and then we will provide some similarities and differences to help you choose the assay that best suits your individual needs.

Continue reading “A BiT or BRET, Which is Better?”

Optimizing Pressure Cycling Sample Preparation for Bottom-Up Proteomics

Posted on by Gary Kobs

Large-scale analyses of the proteome have revealed proteomic changes in response to disease, and these changes hold great promise for diagnostics and treatment of complex diseases if proteomic analysis can be brought into the clinical laboratory. Successful and reliable large-scale proteomics requires sample preparation workflows that are reproducible, reliable and show little variability. To bring proteomics into the clinical laboratory, standardized procedures and workflows for sample prep and analysis are required to generate valid, actionable results on a time scale useful for the clinic.

The two most common sample types analyzed for clinical proteomics are body fluids and tissue biopsies. To process these kinds of samples, there are two initial steps: tissue solubilization, followed by proteolytic digestion. Solubilization of solid tissues is the most labor-intensive and produces the most variable results.

The introduction of pressure cycling technology (PCT) using Barocycler instrumentation has greatly improved both tissue solubilization and digestion consistency. The PCT-based sample preparation protocols generally utilize urea as a lysis buffer for protein denaturing and solubilization. Urea has several drawbacks including inhibiting trypsin activity and introducing unwanted modifications like carbamylation.

Lucas and colleagues analyzed whether replacing urea with SDC would produce similar tissue digestion profiles and improve the PCT method.

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SDC allowed the use of higher temperatures compared to urea, and hence the first step (lysis, reduction, and alkylation) was performed at 56 °C. The second digestion step in the Barocycler was optimized, and the third step was eliminated. To further reduce digestion time, they capitalized on Rapid Trypsin/Lys-C.  Rapid Trypsin/Lys-C maintains robust activity at 70 °C, and allowed Barocycler digestion to be performed in a single step, completing digestion in 30 cycles (approximately 30 min) rather than 105 minutes, streamlining the protocol.

The data presented an improved conventional tissue PCT approach in a Barocycler by replacing urea and proteolytic enzymes with SDC, N-propanol, and modified commercially available enzymes that have higher optimum temperatures.

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Paper Referenced

Lucas, N. et al. (2019) Accelerated Barocycler Lysis and Extraction Sample Preparation for Clinical Proteomics by Mass Spectrometry. J of Proteome Res 18, 399–405.

Related Posts

Cell Free Application: Characterization of Long Non-coding RNA Inhibition of Transcription

Posted on by Gary Kobs

Long noncoding RNAs have been shown to regulate chromatin states, transcriptional activity and post transcriptional activity (1). Only a few studies have observed long non-coding RNAs modulating the translational process (2). The noncoding RNA BC200 has been shown to inhibit translation by interacting with the translation initiation factors, eIF4A and eIF4B.

To characterize how BC200 translational inhibition could be controlled,  a variety of RNAs were transcribed/translated in vitro using the TNT system (Cat. #L4610) from Promega. To each transcription/translation reaction, BC900 RNA, hnRNPE1 and hnRNE2 proteins were added. Inhibition of BC200 activity was noted when proteins were successful expressed (3).

Literature Cited

  1.  Sosinska, P et.al. (2015) Intraperitoneal invasiveness of ovarian cancer from the cellular and molecular perspective. Ginekol. Pol. 86, 782–86.
  2. Geisler, S. and Coller, J. (2013) RNA in unexpected places: long non-coding RNA functions in diverse cellular contexts. Nat.Rev. Mol. Cell. Bio. 14,699–12.
  3. Jang, S. et. al. (2017) Regulation of BC200 RNA-mediated translation inhibition by hnRNP E1 and E2. FEBS Letters. 591, 393–5.

Automated Approach for Multiomic Analysis

Posted on by Gary Kobs

With the use of a suite of “-omics” technologies you can examine the way in which complex cellular processes work together across all molecular domains (i.e., proteomics, metabolomics, transcriptomics) in a single biological system. Several studies have been published across a wide range of fields illustrating the power of such a unified approach (1,2). Most studies however did not focus on the development of a high-throughput, unified sample preparation approach to complement high-throughput “omic” analytics.

A recent publication by Gutierrez and colleagues presents a simple high-throughput process (SPOT) that has been optimized to provide high-quality specimens for metabolomics, proteomics, and transcriptomics from a common cell culture sample (3). They demonstrate that this approach can process  16−24 samples from a cell pellet to a desalted sample ready for mass spectrometry analysis within 9 hours. They also demonstrated that the combined process did not sacrifice the quality of data when compared to individual sample preparation methods.

Literature Cited

1. Roume, H. (2013) Sequential Isolation of Metabolites, RNA, DNA, and Proteins from the Same Unique Sample. Methods Enzymol. 531, 219−236.
2. Lo, A. W. et al. (2017) ‘Omic’ Approaches to Study Uropathogenic Escherichia Coli Virulence. Trends Microbiol. 25, 729−740.
3. Gutierrez, D. et al. (2018)  An Integrated, High-Throughput Strategy for Multiomic Systems Level Analysis J. Proteome Res.

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What’s In YOUR Protein? Optimizing Protease Digestions to Get the Inside Scoop

Posted on by Joliene Lindholm

It’s time to analyze your protein and you are trying to decide where to begin. You are asking questions like: Which protease do I choose? How much enzyme should I use in my digest? How long should I perform my digest?

Unfortunately, there is no one-size fits all answer to this type of question other than… “well it depends.” All protease digests will be a balance between denaturing the protein sample to allow access to cleavage sites, optimizing conditions for the protease to function, and compatibility with your workflow and downstream applications. We provide general guidelines that work for most samples, but frequently you will need to optimize the conditions need for your specific sample and application.

Here, I use the example of a trypsin digest for downstream mass spectrometry to highlight key questions to ask and factors that can be optimized for any digest.

Continue reading “What’s In YOUR Protein? Optimizing Protease Digestions to Get the Inside Scoop”

Of Mice and Microbes: The Science Behind Food Analysis

Posted on by Julia Nepper

In general, people like to know that their food is what the label says it is. It’s a real bummer to find out that beef lasagna you just ate was actually horsemeat. Plus, there are many religious, ethical and medical reasons to be cognizant of what you eat. Someone who’s gluten intolerant and Halal probably doesn’t want a bite of that BLT.

Labels don’t always accurately reflect what is in food. So how do we confirm that we are in fact buying crab, and not whitefish with a side of Vibrio contamination?

For the most part, it comes down to separation science. Scientists and technicians use various chromatographic methods, such as gas chromatography, liquid chromatography, and mass spectrometry, to separate the complex mixture of molecules in food into individual components. By first mapping out the molecular profile of reference samples, they can then take an unknown sample and compare its profile to what it should look like. If the two don’t match up, an analyst would assume that the unknown is not what it claims to be. Continue reading “Of Mice and Microbes: The Science Behind Food Analysis”

Tetanus Neurotoxin: Potential Mechanism for Drug Delivery

Posted on by Gary Kobs

Tetanus neurotoxin (TeNT), produced by Clostridium tetani, is one of the most potent neurotoxins in humans. TeNT causes tetanus, which is characterized by painful muscular contractions and spasms as well as seizure. TeNT is composed of a light chain and a heavy chain (TTH). The toxic properties of TeNT reside in the toxin light chain (L), but like complete TeNT, the TeNT heavy chain (TTH) and the C-terminal domain (TTC) alone can bind and enter into neurons.

Based on these properties, a recent publication (1) considered that TTC could be a promising vehicle to deliver drug cargos to neurons. To explore this possibility, they engineered fusion proteins containing various Tetanus neurotoxin fragments. They chose B-cell leukemia/lymphoma 2 protein (Bcl-2) as a partner protein, because Bcl-2 is one of the most potent anti-apoptotic proteins and has an appropriate size (26kDa) to act as a fusion partner.

They tested these fusion proteins in both cell-based and cell-free protein expression systems to determine whether the purified fusion products retained both anti-apoptotic and neuronal migration properties. One construct (Bcl2-hTTC) exhibited neuronal binding and prevented cell death of neuronal PC12 cells induced by serum and NGF deprivation, as evidenced by the inhibition of cytochrome C release from the mitochondria. For in vivo assays, Bcl2-hTTC was injected into the tongues of mice and was seen to selectively migrate to hypoglossal nuclei mouse brain stems.

  1. Watanbe, Y. et. al. (2018) Tetanus toxin fragments and Bcl-2 fusion proteins : cytoprotection and retrograde axonal migration. BMC Biotechnology 18, 39.

New Recombinant Asp-N Mass Spec Protease: Improved Format and Reduced Price

Posted on by Gary Kobs

Asp-N is a endoproteinase hydrolyzes peptide bonds on the N-terminal side of aspartic residues. The native form is isolated from Pseudomonas fragi. The majority of vendors currently provide a commercial product that consists of 2µg of lyophilized material in a flat bottom vial, and sold for $175–200 US. Formatting such a small amount of material in flat bottom vial can lead to inconsistent resuspension of the protease. Inconsistent working concentrations will lead to non-reproducible data. The current high price also prohibits large-scale use.

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The new recombinant Asp-N protease is cloned from Stenotrophomonas maltophilia and expressed in E. coli. Recombinant Asp-N has similar amino acid cleavage specificity as compared to native Asp-N. Digestion of a yeast extract with native and recombinant Asp-N produces very similar results. Providing 10µg lyophilized material in V-shaped vial with a visible cake enables more consistent re-suspension resulting in reproducible data. Due to improved yields the list price is now approximately 40% less when compared to native enzyme.
Learn more about this new recombinant Asp-N protease.