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.
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. Continue reading “Choosing a Tag for Your Protein”
This is a guest post from Katarzyna Dubiel, marketing intern in Cellular Analysis and Proteomics.
“The objective of my experiment was to test the NanoBRET™ assay as if I was a customer, independent of the research and development team which develops the assay.”
Designing and implementing a new assay can be a challenging process with many unexpected troubleshooting steps. We wanted to know what major snags a scientist new to the NanoBRET™ Assay would encounter. To determine this, we reached out to Laurence Delauriere, a senior applications scientist at Promega-France, who had never previously performed a NanoBRET™ assay. Laurence went step-by-step through the experimental process looking at the CRAF-BRAF interaction in multiple cell lines. In an interview, Laurence provided us with some tips and insights from her work implementing the new NanoBRET™ assay.
In a few words, can you explain NanoBRET?
“NanoBRET is used to monitor protein: protein interactions in live cells. It is a bioluminescence resonance energy transfer (BRET) based assay that uses NanoLuc® luciferase as the BRET energy donor and HaloTag® protein labeled with the HaloTag® NanoBRET™ 618 fluorescent ligand as the energy acceptor to measure the interaction of two binding partners.” Continue reading “Executing a NanoBRET™ Experiment: From Start to Data”
It’s always nice to know that someone is reading your paper. It’s a sign that your research is interesting, useful and actually has an impact on the scientific community. We were thrilled to learn that papers published by Promega scientists made the top 10 most read papers of 2017 in the journal ACS Chemical Biology. In fact, Promega scientists authored five of the top six most read papers! Let’s take a look at what they are.
This 2017 paper introduces our newest star: HiBiT, a tiny 11aa protein tag. To any scientist studying endogenous protein expression, the HiBiT Tagging System is your dream come true. It combines quantitative and highly sensitive luminescence-based measurement with a tiny-sized tag that can be easily inserted into endogenous protein via CRISPR/Cas9 gene editing with little impact on native protein function. The HiBiT Tagging System has been listed as a 2017 Top 10 Innovation by The Scientist, and it will drastically change how we study endogenous protein expression. Continue reading “Top 5 Most Read Promega Papers in 2017”
Antibodies labeled with small molecules such as fluorophore, biotin or drugs play a critical role in various areas of biological research,drug discovery and diagnostics. There are several limitations to current methods for labeling antibodies including the need for purified antibodies at high concentrations and multiple buffer exchange steps.
In a recent publication, a method (on-bead conjugation) is described that addresses these limitations by combining antibody purification and conjugation in a single workflow. This method uses high capacity-magnetic Protein A or Protein G beads to capture antibodies directly from cell media followed by conjugation with small molecules and elution of conjugated antibodies from the beads.
Using a variety of fluorophores the researchers show that the on-bead conjugation method is compatible with both thiol- and amine-based chemistry.
This method enables simple and rapid processing of multiple samples in parallel with high-efficiency antibody recovery. It is further shown that recovered antibodies are functional and compatible with downstream applications.
Robert Hooke first coined the term “cell” after observing plant cell walls through a light microscope—little empty chambers, fixed in time and space. However, cells are anything but fixed.
Cells are dynamic: continually responding to a shifting context of time, environment, and signals from within and without. Interactions between the macromolecules within cells, including proteins, are ever changing—with complexes forming, breaking up, and reforming in new ways. These interactions provide a temporal and special framework for the work of the cell, controlling gene expression, protein production, growth, cell division and cell death.
Visualizing and measuring these fluid interactions at the level of the cell without perturbing them is the goal of every cell biologist.
Antibodies labelled with radioisotopes or the sequential administrationof an antibody and a radioactive secondary agent facilitate the in vivo detection and/or characterisation of cancers by positron emission tomography (PET) or by single-photon emission computed tomography (SPECT) imaging.
There are drawbacks to both methods, including prolonged exposure to radiation and ensuring that both the antibody and the radiolabelled secondary agent are suitably designed so that they bind rapidly upon contact at the tumor.
A recent publication (1) investigated a alternative method utilizing the HaloTag® dehalogenase enzyme HaloTag® is a dehalogenase enzyme (33 kDa) that contains an engineered cavity designed to accommodate the reactive chloroalkane group of a HaloTag® ligand (HTL). Upon entering the enzyme cavity, the terminal chlorine atom rapidly undergoes nucleophilic displacement, and a covalent adduct is formed, effectively anchoring the HaloTag® ligand in a precise location.
Three new HaloTag® ligands were synthesized and each labelled with the SPECT radionuclide indium-111 111In-HTL-1 and the dual-modality HaloTag® ligands,111In-HTL-2 and111;In-HTL-3 containing TMR which allows complementary imaging data).
For the validation of the pretargeting strategy based on these HaloTag® ligands, the target human epidermal growth factor receptor 2 (HER2)was selected. Trastuzumab (Herceptin®) was selected as the primary targeting agent and was modified with HaloTag® protein via the trans-cyclooctene/tetrazine ligation.
All three 111In-labelled HaloTa®g ligands exhibited significantly higher binding to the HER2 expressing when compared to negative controls.
If you are trying to investigate protein:protein interactions inside cells, you know how important physiologically relevant results are. If you overload your cells with fusion constructs, your protein interactions may not actually reflect what is going on in the cell, and if your BRET energy donor and acceptor do not have sufficiently separated spectra, you can pick up a fair amount of noise in your experiment. Using the new superbright NanoLuc® Luciferase, and the HaloTag® Technology, we have developed a sensitive BRET system to help you take a better look specific protein interactions that interest you. Promega research scientist, Danette Daniels, describes the system in the Chalk Talk below:
Tumor cells are characterized by many features: including uncontrolled proliferation, to loss of contact inhibition, acquired chromosomal instability and gene copy number changes among them. Some of those copy number changes are site-specific, but very little is known about the mechanisms or proteins involved in creating site-specific copy number changes. In a recently published Cell paper, Black and colleagues, propose a mechanism for site-specific copy number variations involving histone methylation proteins and replication complexes.
Previous work from Klang et al. had shown that local amplification of chromosomal regions occurs during S phase and that chromatin structure plays a critical role in this amplification (2), and other work by Black and colleagues (3) implicated KDM4A in changing timing of replication by altering chromatin accessibility in specific regions. Other research also had shown that KDM4A protein levels influence replication initiation and that KDM4A has a role in some DNA damage response pathways (4,5). Looking at the body of work, Black et al. hypothesized that KDM4A, with its roles in replication, might possibly provide link into the mechanism of site-specific copy number variation in cancer. Continue reading “Site-specific copy number variations in cancer: A story begins to unfold”
Back when I was a graduate student (more than a few years ago), I remember hearing another student joke that if a member of his thesis committee asked him to explain an unexpected or unusual result, he was going to “blame” epigenetics. At that time, the study of epigenetic gene regulation was in its infancy, and scientists had much to learn about this mysterious regulatory process. Fast forward to today, and you’ll find that scientists know a lot more about basic epigenetic mechanisms, although there is still plenty to learn as scientists discover that the topic is much more complicated than initially thought, as is often the case in science. A recent EMBO Journal article is contributing to our knowledge by shedding light on the role of the TET family of DNA-modifying enzymes in epigenetics (1).
Tiny particles found in clothing, cosmetics, food, electronics or furniture enter our bodies and behave in unexpected (sometimes unwanted) ways. However, in the realm of medicine another type of particle called the nanoparticle can bring untold potential. We can load them with drugs, for example, and deliver them precisely to a diseased organ or cell. Mark Davis from the California Institute of Technology has created nanoparticles that deliver siRNA specifically into melanomas. Davis and his colleagues have not shied away from making bold claims about the therapeutic potential of their work. They write:
“When taken together, the data presented here provide the first, to our knowledge, mechanistic evidence of RNAi in a human from an administered siRNA. Moreover, these data demonstrate the first example of dose-dependent accumulation of targeted nanoparticles in human tumours. ….These data demonstrate that RNAi can occur in a human from a systemically delivered siRNA, and that siRNA can be used as a gene-specific therapeutic.” Davis et al. 2010.Continue reading “Nanoparticles – Workhorses That Bring Tremendous Benefit”