Factors Influencing Compound Potency in Biochemical and Cellular Assays

Late in 2017, a group here at Promega launched an exciting new assay, the NanoBRET™ Target Engagement (TE) Intracellular Kinase Assay.

It’s easy for me to call this assay exciting; I was an editor on the project team. But judging by the reviews on the SelectScience® web site, others are excited about NanoBRET™ Target Engagement Intracellular Kinase Assay too.

A review of the NanoBRET TE Kinase assay from SelectScience® .

A review of the NanoBRET TE Kinase assay from SelectScience® .

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Millions of Pickles, Pickles in the Sea

For a few years beginning late in 2013, warmer ocean conditions in the eastern Pacific prompted the appearance of unexpected species and toxic algal blooms that devastated others. When temperatures cooled in 2017, the marine ecosystems seemed to be returning to normal. Except for the pyrosomes. Although these previously rare organisms did start to wash up on beaches during the periods of warming, they began to appear by the millions from Oregon to Alaska that spring.


Photo by Steven Grace.

Some combination of ideal conditions led pyrosomes to multiply, dominate the ocean surface and wash up on beaches along the US and Canadian Pacific Coasts. Pyrosomes typically exist offshore, far below the surface in warm, tropical waters all over the world. Their sudden proliferation in other areas is likely due to the warm, Pacific ocean “blob,” although atypical sea currents and changes in pyrosome diet have been offered as other possible explanations.

While the appearance of pyrosomes impeded the efforts of fisherman by clogging nets and filling hooks, greater ecological effects have yet to be observed. As we celebrate World Oceans Month, pyrosomes offer a mesmerizing example of the astounding biological diversity our oceans have to offer and, perhaps, a cautionary tale of the impact climate change can have on those marine lifeforms.

The pyrosome species common in the NE Pacific, Pyrosoma atlanticum, goes by a few other colorful names. Each name reveals something captivating about these creatures. Commonly called “sea pickles” due their size, shape and bumpy texture (like a transparent cucumber), these are not single organisms, but colonies formed by hundreds or thousands of individual multicellular animals call zooids.

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

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.

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.

High-Throughput Purification with Experts Included

Implementing automated nucleic acid purification or making changes to your high-throughput (HT) workflow can be complicated and time-consuming. There are also many barriers to success such as challenging samples types and maintaining desirable downstream results that can add to the stress, not to mention actually getting the robotic instrumentation to do what you want it to. All of this makes it easy to understand why many labs avoid automating or own expensive instrumentation that goes unused. Continue reading

Catalyzing Solutions with Synthetic Biology

Computer-generated model of a virus.

The keynote speaker for this year’s International Symposium on Human Identification (ISHI), Andrew Hessle, describes himself as a catalyst for big projects and ideas (1). In biology, catalysts are enzymes that alter the microenvironment and lower the energy of activation so that a chemical reaction that would proceed anyway happens at a much faster rate—making a reaction actually useful to the biological system in which it occurs.

In practical terms, Andrew Hessel is the person who helps us over our inertia. Instead of waiting for someone else, he sees a problem, gathers an interested group of people with diverse skills and perspectives, creates a microenvironment for these people to interact, and runs with them straight toward the problem. Boom. Reaction started.

One of the problems he has set his mind toward is that of cancer drug development. Continue reading

Kinase Drug R & D: Helping Your Inhibitor Make the Cut

Finding the best inhibitor for your kinase doesn’t have to be a long trip.

A recent paper in Journal of Medicinal Chemistry, “Discovery of GDC-0853: A Potent, Selective and Noncovalent Bruton’s Tyrosine Kinase Inhibitor in Early Clinical Development” (1) details some elegant work in chemical modification and extensive testing during exploration of inhibitors for BTK. As a warmup to the article, here is a brief BTK backstory.

BTK (Bruton Tyrosine Kinase): Importance in Health and Disease 

Bruton’s tyrosine kinase (BTK) was initially identified as a mediator of B-cell receptor signaling in the development and functioning of adaptive immunity. More recent and growing evidence supports an additional role for BTK in mononuclear cells of the innate immune system, especially dendritic cells and macrophages. For example, BTK functions in receptor-mediated recognition of infectious agents, cellular maturation and recruitment processes, and Fc receptor signaling. BTK has recently been identified as a direct regulator of a key innate inflammatory machinery, the NLRP3 inflammasome (2). Continue reading

Kinase Inhibitors as Therapeutics: A Review

The review “Kinase Inhibitors: the road ahead” was recently published in Nature Reviews Drug Discovery. In it, authors Fleur Ferguson and Nathanael Gray provide an up-to-date look at the “biological processes and disease areas that kinase-targeting small molecules are being developed against”. They note the related challenges and the strategies and technologies being used to efficiently generate highly-optimized kinase inhibitors.

This review describes the state of the art for kinase inhibitor therapeutics. To understand why kinase inhibitors are so important in the development of cancer (and other) therapeutics research, let’s start with the role of kinases in cellular physiology.

The road ahead for kinase inhibitor studies.

Why Kinases? Continue reading

Beer Is Complicated: Proteome Analysis via Mass Spectrometry

still life with a keg of beer and draft beer by the glass.The art of brewing alcoholic beverages has existed for thousands of years. The process of beer brewing begins with barley grains, which are malted to allow partial germination, triggering expression of key enzymes. The germinated grains are then dried and milled. Next, starch, proteins, and other molecules are solubilized during mashing. During mashing, solubilized enzymes degrade starch to fermentable sugars, and digest proteins to produce peptides and free amino acids. Fermentable sugars and free amino acids are required for efficient yeast growth during fermentation.

After the mash, the wort is removed, and hops are added for bitterness and aroma, and the wort is boiled. After boiling, the wort is inoculated with yeast, and fermentation proceeds to produce bright beer. Typically this bright beer is then filtered, carbonated, packaged, and sold. Many proteins originating from the barley grain and the yeast are present in beer, and these have been reported to affect the quality of the final product. However, some of the biochemical details of this process remain unclear. To better understand what happens during the various steps of the brewing process,  Schultz et al. used mass spectrometry proteomics to perform a global untargeted analysis of the proteins present across time during beer production and described this work in a recent paper (1). Samples analyzed included sweet wort produced by a high temperature infusion mash, hopped wort, and bright beer. Continue reading

Characterizing Multi-Subunit Protein Complexes Using Cell-Free Expression

artist's concept of a cell membraneMulti-subunit protein complexes control membrane fusion events in eukaryotic cells (1). CORVET and HOPS are two such multi-subunit complexes, both containing the Sec1/Munc18 protein subunit VPS33A (2). Metazoans additionally possess VPS33B, which has considerable sequence similarity to VPS33A but does not integrate into CORVET or HOPS complexes and instead stably interacts with VIPAR. Recent research suggests that VPS33B and VIPAR comprise two subunits of a novel multi-subunit complex analogous in configuration to CORVET and HOPS (3).

In a recent publication (4), Hunter and colleagues, further characterized the VPS33B and VIPAR complex. Using co-immunoprecipitation and proximity-based ligation assay, they identified two novel VPS33B-interacting proteins, VPS53 and CCDC22.

In vitro binding experiments, VPS33B and GST-VIPAR were co-expressed in Escherichia coli and purified by GSH affinity. The VPS33B/GSTVIPAR complex was used as bait in pulldown experiments, with myc-CCDC22 and myc-VPS53 expressed by cell-free in vitro transcription/translation in wheat germ lysate. Myc-CCDC22 was very efficiently pulled down by VPS33B/GST-VIPAR, whereas myc-VPS53 was not .The interaction between VPS53 and the VPS33B-VIPAR complex was either indirect, requires other proteins contribute to the interaction, or requires a post-translational modification not conferred in the plant cell-free expression system (wheat germ). Pull-down experiments with individual subunits or expressing as complexes, was inefficient and did not result in binding to VPS33B/GST-VIPAR.

To further understand how VPS33B-VIPAR may interact with CCDC22, Hunter and colleagues attempted to refine the region of CCDC22 that interacts with VPS33B/GST-VIPAR by generating a series of truncated forms of CCDC22. However, none of five CCDC22 truncations were able to bind to VPS33B/GST-VIPAR. The hypothesis was that truncated forms of CCDC22 are unstable and unable to fold correctly in this assay system.

Additional experiments noted that the protein complex in HEK293T cells which contained VPS33B and VIPAR was considerably smaller than CORVET/HOPS, suggesting that, unlike VPS33A, VPS33B does not assemble into a large stable multi-subunit protein complex.


  1. D’Agostino, M. et. al. (2017) A tethering complex drives the terminal stage of SNARE-dependent membrane fusion. Nature 551, 634–638.
  2. Balderhaar, H. J. K. and Ungermann, C. (2013) CORVET and HOPS tethering complexes – coordinators of endosome and lysosome fusion. J. Cell Sci. 126, 1307–16.
  3. Spang, A. (2016) Membrane Tethering Complexes in the Endosomal System. Front. Cell Dev. Biol. 4, 35.
  4. Hunter, M.  et. al.  (2017) Proteomic and biochemical comparison of the cellular interaction partners of human VPS33A and VPS33B. [Internet bioRxiv http://dx.doi.org/10.1101/236695  Accessed 3/12/2018]

A Better Way to Understand How and Why Cells Die

Real-time, up-to-the-minute access to information provides new opportunities for scientists to monitor cellular events in ever more meaningful ways. Real-time cytotoxicity and cell viability assay reagents now allow constant monitoring of cell health status without the need to lyse or remove aliquots from plates for measurement. With a real-time approach, data can be collected from cell cultures or microtissues at multiple time points after addition of a drug compound or other event, and the response to treatment continually observed.

The CellTox™ Green assay is a real-time assay that monitors cytotoxicity using a fluorescent DNA binding dye, which binds DNA released from cells upon loss of membrane integrity. The dye cannot enter intact, live cells and so fluorescence only occurs upon cell death, correlating with cytotoxicity. Here’s a quick overview showing how the assay works:

More Data Using Fewer Samples and Reagents
The ability to continually monitor cytotoxicity in this way makes it easy to conduct more than one type of analysis on a single sample. Assays can be combined to determine not only the timing of cytotoxicity, but to also understand related events happening in the same cell population. As long as the readouts can be distinguished from one another multiple assays can be performed in the same well, providing more informative data while using less cells, plates and reagents.

Combining assays in this way can reveal critical information regarding mechanism of cell death. For example, assay combinations can be used to determine whether cells are dying from apoptosis or necrosis, or to distinguish nonproliferation from cell death. Combining CellTox Green with an endpoint luminescent caspase assay or a real-time apoptosis assay allows you to determine whether observed cytotoxic effects are due to apoptosis. Cytotoxic and anti-proliferative effects can be distinguished by combining the cytotoxicity assay with a luminescent or fluorescent cell viability assay. Continue reading