Protein Analysis and Purification

Giant Rodent, Lowered Cancer Rates: What Genetic Analysis Reveals about the Capybara and Cancer

Posted on by Kari Kenefick

Do you find the thought of a giant rodent off-putting? Do your thoughts go to huge rats running amuck in dark allies, threatening unsuspecting passers by?

I personally hold rodents in low esteem. Rats, mice…who needs them? With the exception of cavies. I spent countless hours as a child playing with guinea pigs. We had as many as 16 of these little rodents at one time (the males are very capable of chewing or climbing out of cardboard boxes to reach a female in the next box). The baby guinea pigs were very cute and the adults had quite pronounced personalities, and a lot of attitude.

It was this history with guinea pigs that made me interested in learning more about the largest rodent in the world, the South American capybara (Hydrochoerus hydrochaeris). These family-oriented herbivores are found in savannas and forested areas, living in groups of as many as 100 members. They are excellent swimmers and can remain underwater for as long as 5 minutes. In fact, capybara mate only in the water. (Perhaps it’s not surprising then that the South American alligator, the caiman, is one of the capybara’s greatest predators.)

Photos of an adult male capybara.
A male capybara, with a scent gland (called a morillo) on his head. Photo by: Charles J Sharp – Own work, from Sharp Photography, sharpphotography, CC BY-SA 4.0.

With their squared-off nose and lack of tail, capybaras actually resemble guinea pigs. However, these oversized cavies weigh as much as 40 pounds. and can reach 24” at the shoulder, the size of an average standard poodle. Guinea pigs, on the other hand, weigh in at 2–3 pounds, and are 3–4” tall.

Their proportions make capybaras 60 times more massive than their closest relatives, rock cavies (Kerodon sp.) and 2,000 times more massive than the common mouse (Mus musculus). This tremendous size difference is why Herrera-Álvarez et al. took a closer look at the capybara, studying its propensity to develop cancer and other tradeoffs that would seem to coincide with its exceptional size.

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Targeted Protein Degradation: A Bright Future for Drug Discovery

Posted on by Ken Doyle
targeted protein degradation and protacs

Our cells have evolved multiple mechanisms for “taking out the trash”—breaking down and disposing of cellular components that are defective, damaged or no longer required. Within a cell, these processes are balanced by the synthesis of new components, so that DNA, RNA and proteins are constantly undergoing turnover.

Proteins are degraded by two major components of the cellular machinery. The discovery of the lysosome in the mid-1950s provided considerable insight into the first of these degradation mechanisms for extracellular and cytosolic proteins. Over the next several decades, details of a second protein degradation mechanism emerged: the ubiquitin-proteasome system (UPS). Ubiquitin is a small, highly conserved polypeptide that is used to selectively tag proteins for degradation within the cell. Multiple ubiquitin tags are generally attached to a single targeted protein. This ill-fated, ubiquitinated protein is then recognized by the proteasome, a large protein complex with proteolytic activity. Ubiquitination is a multistep process, involving several specialized enzymes. The final step in the process is mediated by a family of ubiquitin ligases, known as E3.

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CRISPR/Cas9 Knock-In Tagging: Simplifying the Study of Endogenous Biology

Posted on by Ken Doyle

Understanding the expression, function and dynamics of proteins in their native environment is a fundamental goal that’s common to diverse aspects of molecular and cell biology. To study a protein, it must first be labeled—either directly or indirectly—with a “tag” that allows specific and sensitive detection.

Using a labeled antibody to the protein of interest is a common method to study native proteins. However, antibody-based assays, such as ELISAs and Western blots, are not suitable for use in live cells. These techniques are also limited by throughput and sensitivity. Further, suitable antibodies may not be available for the target protein of interest.

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NanoLuc: Tiny Tag with a Big Impact

Posted on by Darcia Schweitzer

Synthetic biology—genetically engineering an organism to do or make something useful—is the central goal of the iGEM competition each year. After teams conquer the challenge of cloning their gene, the next hurdle is demonstrating that the engineered gene is expressing the desired protein (and possibly quantifying the level of expression), which they may do using a reporter gene.

Reporters can also play a more significant role in iGEM projects when teams design their organism with reporter genes to detect and signal the presence of specific molecules, like environmental toxins or biomarkers. Three of the iGEM teams Promega sponsored this year opted to incorporate some version of NanoLuc® Luciferase into their projects.

NanoLuc® luciferase is a small monomeric enzyme (19.1kDa, 171 amino acids) based on the luciferase from the deep sea shrimp Oplophorus gracilirostris. This engineered enzyme uses a novel substrate, furimazine, to produce high-intensity, glow-type luminescence in an ATP-independent reaction. Unlike other molecules for tagging and detecting proteins, NanoLuc® luciferase is less likely to interfere with enzyme activity and affect protein production due to its small size.

NanoLuc® Luciferase has also been engineered into a structural complementation reporter system, NanoBiT® Luciferase, that contains a Large subunit (LgBiT) and two small subunit options: low affinity SmBiT and high affinity HiBiT. Together, these NanoLuc® technologies provide a bioluminescent toolbox that was used by the iGEM teams to address a diverse set of biological challenges.

Here is an overview of each team’s project and how they incorporated NanoLuc® technology.

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Choosing a Tag for Your Protein

Posted on by Sara Klink

You have identified and cloned your protein of interest, but you want to explore its function. A protein fusion tag might help with your investigation. However, choosing a tag for your protein depends on what experiments you are planning. Do you want to purify the protein? Would you like to identify interacting proteins by performing pull-down assays? Are you interested in examining the endogenous biology of the protein? Here we cover the advantages and disadvantages of some protein tags to help you select the one that best suits your needs.

Immunofluorescent detection of HiBiT-tagged proteins in CRISPR-edited cell pools and clones using the Anti-HiBiT Monoclonal Antibody.
CRISPR-Cas9 editing knocked-in HiBiT at the endogenous locus of proteins with varying subcellular localization. Fixed CRISPR-modified clones or pools of cells were imaged by immunofluorescent staining using the Anti-HiBiT Monoclonal Antibody (red) and Hoechst dye (blue). Panel A. VCL-HiBiT pool. Panel B. SMARCA4-HiBiT clone. Panel C. HDAC2-HiBiT clone. Panel D. HSP90B1-HiBiT pool.

Affinity Tags

The most commonly used protein tags fall under the category of affinity tags. This means that the tag binds to another molecule or metal ion, making it easy to purify or pull down your protein of interest. In all cases, the tag will be fused to your protein of interest at either the amino (N) or carboxy (C) terminus by cloning into an expression vector. This protein fusion can then be expressed in cells or cell-free systems, depending on the promoter the vector contains.

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Looking Back: Cell-Free Expression Systems Helped to Characterize Proteins Involved in Hypoxia Response

Posted on by Gary Kobs
Structur of a HIF-1a-pVHL-ElonginB-ElonginC complex
Structure of a HIF-1a-pVHL-ElonginB-ElonginC complex

William G. Kaelin Jr., Sir Peter J. Ratcliffe and Gregg L. Semenza were awarded the 2019 Nobel Prize in Physiology or Medicine for their discoveries of how cells sense and adapt to oxygen availability.

Kaelin and Ratcliffe’s labs focused their efforts on the transcription factor HIF (hypoxia-inducible factor). This transcription factor is critical in the cellular adaptation of to changes in oxygen availability.

When oxygen levels are elevated cells contain very little HIF. Ubiquitin is added to the HIF protein via the VHL complex and it is degraded in the proteasome.  When oxygen levels are low (hypoxia) the amount of HIF increases.

In 2001 both groups published articles characterizing the interaction between VHL and HIF, and these articles were referenced by the Nobel Prize Organization in their press release about this year’s award. (1,2). Both studies demonstrated that under the normal oxygen conditions hydroxylation of proline residue P564 enabled VHL to recognize and bind to HIF.

The use of cell free expression (i.e., TNT Coupled Transcription/Translation System) by both labs was key in the characterization of the VHL:HIF interaction The labs utilized HIF and VHL 35-S labeled proteins generated via the TNT system under both normal or in a hypoxic work station to:

  • Determine the affect of ferrous chloride and cobaltous chloride on the interaction
  • Map the specific region of HIF required for the interaction to occur (556-574)
  • Determine the effect of HIF point mutations on the interaction
  • Use synthetic peptides to block the interaction
  • Conclude that a factor in mammalian cells was necessary for the interaction to occur.

Literature Cited

  1. Ivan, M et al. (2001) HIF Targeted for VHL-Mediated Destruction by Proline Hydroxylation: Implications for O2 Sensing. Science 292: 464–67.
  2. Jaakkola, P. et al. (2001) Targeting of HIF-α to the von Hippel-Lindau Ubiquitylation of Complex by O2– Regulated Prolyl Hydroxylation. Science 202, 468–72 .

Related Posts

All You Need is a Tether: Improving Repair Efficiency for CRISPR-Cas9 Gene Editing

Posted on by Sara Klink

Ribonucleoprotein complex with Cas9, guide RNA and donor ssDNA. Copyright Promega Corporation.

With the advent of genome editing using CRISPR-Cas9, researchers have been excited by the possibilities of precisely placed edits in cellular DNA. Any double-stranded break in DNA, like that induced by CRISPR-Cas9, is repaired by one of two pathways: Non-homologous end joining (NHEJ) or homology-directed repair (HDR). Using the NHEJ pathway results in short insertions or deletions (indels) at the break site, so the HDR pathway is preferred. However, the low efficiency of HDR recombination to insert exogenous sequences into the genome hampers its use. There have been many attempts at boosting HDR frequency, but the methods compromise cell growth and behave differently when used with various cell types and gene targets. The strategy employed by the authors of an article in Communications Biology tethered the DNA donor template to Cas9 complexed with the ribonucleoprotein and guide RNA, increasing the local concentration of the donor template at the break site and enhancing homology-directed repair. Continue reading “All You Need is a Tether: Improving Repair Efficiency for CRISPR-Cas9 Gene Editing”

Brazilian University Swatting at Leishmaniasis Parasite

Posted on by Julia Nepper

The Medicinal Chemistry Center (CQMED), headquartered at Campinas State University in Brazil, recently started a project in partnership with Promega to develop drugs that can be used against Leishmania. This genus of protozoans is the etiological agent of leishmaniasis, transmitted to humans by sandflies.

Microscopic image of Leishmania parasite
Microscopic image of Leishmania tropica. Credit: Brian E. Keas at Michigan State University.

Leishmaniasis is classified as a neglected tropical disease that mainly affects poor communities. Symptoms include large skin sores and an enlarged spleen. The challenge in developing drugs to treat Leishmania is finding appropriate therapeutic targets. These targets are normally proteins whose inhibition leads to death of the parasite. In addition to pharmaceutical company Eurofarma, whose goal is to develop drugs for Leishmania, Promega was chosen to help solve this problem because of our NanoBRET™ Target Engagement (TE) assay*, a well-established technique for measuring protein interactions. In this assay, NanoLuc® luciferase is attached to the protein of interest, and a fluorescent NanoBRET™ tracer molecule is added to the cells. This produces a BRET signal. When a competing ligand is added, it will displace the tracer molecule, enabling quantification of the strength of the interaction compared to the tracer molecule..

A challenge that researchers will face will be ensuring that the NanoBRET™ tracer reaches the inside of the parasite cells; because Leishmania is an intracellular parasite, molecules need to cross the host cell membrane, the membrane of the vacuole containing the parasites, and the membrane of the parasite itself. Another challenge the slow reproduction of Leishmania within macrophages. On top of that is the fact that the parasite’s metabolism varies depending on its biological cycle, meaning that there could be long periods of time during which a drug’s therapeutic target is not expressed in the cell, during which time the drug would have no effect. The ideal target would be expressed at high levels throughout the cell cycle.

The project is being led by Rafael Couñago, a researcher at CQMED, and Promega scientists Matt Robers and Jean-Luc Vaillaud.

*An earlier version of this blog incorrectly said that these experiments are based on the NanoBRET™ assay using HaloTag® protein.

PROTACs, PHOTACs and LYTACs: How to Target a Protein for Degradation

Posted on by Sara Klink
PROTACs for Targeted Protein Degradation
An illustration of PROTAC structure and the proteins it binds.

Targeting a single protein and making it disappear from the cell is quite the magic trick, and there are various molecular tools available for this task. You can use RNA interference, which prevents a protein from being made, inhibitors that bind the protein, rendering it unavailable for use or even gene editing tools like CRISPR that can remove it from the genome. But did you know that you can target an existing protein for destruction, using the cell’s own garbage disposal system to degrade the protein? All you need is a molecule that can connect your protein to one with a role in cellular protein degradation and your protein can be destroyed.

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Lighting Up GPCR Research with Bioluminescent Tagging

Posted on by Julia Nepper

G Protein-Coupled Receptors (GPCRs) are a very large, diverse family of transmembrane receptors in eukaryotes. These receptors detect molecules outside the cell and activate internal signaling pathways by coupling with G proteins. Once a GPCR is activated, β-arrestins translocate to the cell membrane and bind to the occupied receptor, uncoupling it from G proteins and promoting its internalization.

Reporter tags are useful for studying the dynamics of GPCRs and associated proteins, but large tags can disrupt the receptors’ native functioning, and often overexpression of the tagged protein is required to obtain sufficient signal. Here is one example of how researchers have used the small, bright NanoLuc® luciferase to overcome these common challenges and answer questions about GPCRs.

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