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Protein Expression and Analysis

Top Five Methods for Primary Antibody Labeling

In any application that uses antibodies for signal detection (e.g., Western blotting, ELISA, immunohistochemistry, or FACS), there are two approaches to antibody labeling: direct and indirect labeling. Standard Western blotting uses indirect labeling because you use a primary antibody to detect the target antigen, followed by a secondary antibody to which a detection molecule is…

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An Experimental Tool-kit for Measuring Protein Stability

Proteins in the cell are in a constant flux governed by events including synthesis and degradation. In an effort to make cells more efficient by reducing the unnecessary protein load, most proteins in the cell have a specifically defined half-life. Another reason why cells have evolved to degrade proteins is to ensure timely removal of…

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Helpful Tips Before Your First Rho Pull-Down Assay

If you have studied cellular movement or cell division, you have encountered Rho in the literature, because it regulates both processes. And the list of roles for Rho in the cell continues to grow! The prominence of Rho in the biology of non-diseased and diseased cells has caused researchers to continually optimize the Rho pull-down…

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Troubleshooting a Faulty ELISA

Is ELISA giving you the blues? The frustrating kind, not the lovely kind you get while watching the enzyme substrate reaction! This age old assay has the perks of being quick and fairly simple to perform, but when conditions are not perfect, ELISAs can deliver less than optimal results, and fail to be consistent and…

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Protein Self-Labeling with Halo, SNAP, and CLIP Tagging

We all know the impact fluorescent proteins have had in advancing cell biology. Although fluorescent proteins have revolutionized the field, they aren’t perfect and like all things research, they have their limitations. If you’re looking for a genetic tool with superior fluorescent properties, or one that allows you to introduce a variety of labels into…

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iPOND, Part 2: Why Should You Go Fishing with iPOND?

In part 1, ‘iPOND: Fishing for Proteins with DNA as Bait’ we went on a fishing expedition and learned how the iPOND technique can help us investigate the protein landscape of DNA synthesis. In this article, we will pit iPOND against a few other widely used techniques in order to answer the question: ‘Why should…

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Quantifying Individual Proteins Per Bacterial Cell

I’m a simple molecular biologist. It’s awesome how computational biologists use math to reduce and rebuild biological phenomenon. In my own way, I also like to reduce my observations to numbers. As a budding biochemist, I need to assemble and quantify the players in my pathway to truly understand it. In particular, I am interested…

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Modeling – in the World of Proteins

Computational protein structure prediction provides three-dimensional structures of proteins that are predicted by in-silico techniques. Such protein modeling relies on principles from known protein structures obtained via x-Ray crystallography, NMR Spectroscopy, as well as from physical energy functions.  There are three main methods of modeling: The first and favorite method is Homology Modeling,1-2 Followed by the…

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iPOND, Part 1: Fishing for Proteins with DNA as Bait

No, iPOND is not a sleek electronic fishing device from Apple. However, if you thought about fishing, well, you’re not far off the mark. If you find yourself wondering which proteins are present at DNA during or after replication, iPOND is an elegant technique to help you find out. In this article, I will explain…

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An Introduction to In-Gel Zymography

Enzymes are special among proteins. It is not enough to detect them. You need to know their activity level. If you have devoted a substantial part of your research to studying proteases, like I did, you’ll know how crucial it is to choose an appropriate enzyme assay. There’s a heap of lab techniques out there…

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How to Prepare Biological Metallo-Proteins

The first thing one might notice when working with metallo-proteins is that they offer unique, colorful reactions.  These colorful reactions are based not only on the metal, but the ligand, or coordinating molecules.  Approximately 80% of proteins contain inorganic cofactors like iron (Fe) and copper (Cu) metals necessary to catalyze a reaction.  Understanding how these…

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Brefeldin A v Monensin: How to Hunt for Proteins

As any good biologist knows, one of the easiest ways to determine if a cell is functionally active is the production and secretion of proteins in response to a stimulus. In many circumstances, the quantity of the secreted protein, and thus the level of cellular activation can be assessed by ELISA. However, if you are…

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Taking up the Challenges of In Vitro Monoclonal Antibody Production

Monoclonal antibodies are extensively used in research laboratories, diagnostic products and immunotherapy and have multiple advantages over polyclonal antibodies. They exhibit enhanced specificity to single epitopes, have little or no variability, and are easy to modify and customize as required. The History of Monoclonal Antibodies In 1984, Georges Köhler, César Milstein, and Niels Jerne received…

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Codon Optimization for Increased Protein Expression

The Genetic Code: A Universal Template for Protein Translation All known organisms share the ‘central dogma’ of molecular biology. DNA is transcribed into mRNA that is translated into protein. During the discovery of the genetic code, Francis Crick hypothesized that translation required a mediator to aid mRNA-guided translation according to a number of specifics. Amongst…

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Antibody Validation

Not all antibodies are valid for every experiment and condition, and they must be validated for the specific application and species. Currently, there is no standard means of “antibody validation,” and this can greatly impact experimental reproducibility and reliability. Journals and granting agencies have taken steps to address this gap. Many now require you to…

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Introduction to DREADDs – Control Over G Protein Coupled Receptor GPCR signaling

Gee, Protein, What Do You Do? Manipulation of a system under investigation is the backbone of experimentation. A new tool called Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) allows us to hijack cell signaling and study cell function within living organisms. Like its cousin technique, optogenetics, DREADD technology uses a viral vector to introduce…

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A Primer on Phage Display Libraries

Phage display – the process of genetically fusing antibody fragments with phage to identify binding partners to your protein of interest – was covered pretty thoroughly here over the past few months. The success of this assay predicates on creating a diverse library of up to 1012 genes coding for these antibody fragments. Despite being…

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ELISA: How I Wonder What You Are

My phone’s email notification went off, and I rolled over in bed to look at the clock. Saturday, 5 am. Wonderful. Who would email me at that hour? It had to be my undergraduate research PI. I unlocked my phone. Yep. Doesn’t he ever sleep? Dear Casey: We are launching a new collaborative project in…

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Explained: Sensor Chips for Surface Plasmon Resonance and Other Applications

Biosensor chip selection is a critical step in planning and running a surface plasmon resonance (SPR) experiment. Chip selection depends on the ligand or target that needs to be immobilized on the sensor chip, the analyte that is flowed over the target to study the binding, and the purpose of the biosensor assay (i.e., determination…

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Development of a Potential Recombinant Protein Vaccine in E. Coli

Expression and Purification of an Engineered, E. coli-expressed Leishmania donovani Nucleoside Hydrolase with Immunogenic Properties Potential recombinant protein vaccine candidates must meet several criteria: They must be expressed at sufficiently high levels in the organism of choice They must be purified to high purity from the expression system in an immunogenic form They must induce…

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How to Store Your Concentrated Proteins

Like graduate students, proteins are sensitive to rough handling. This is particularly true when they (the proteins, not the students!) are being concentrated, purified, and stored. We’ve covered the many options out there for concentrating your proteins, along with how to handle protein extracts to keep your proteins safe from degradation. But proteins can degrade…

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How to Choose Quality Antibodies for Successful Western Blotting

Successful western blotting means achieving unambiguous results, and this requires a sensitive and specific antibody-antigen interaction. Consequently, high quality antibodies are critical for reliable and consistent western blotting. Western Blotting Process In the basic western blotting process, polyacrylamide gel electrophoresis (PAGE) separates a mix of proteins according to their molecular weights (denaturing gels) or their…

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Fluorescent Western Blotting: Lowdown and Advantages

In this article, you will be introduced to the world of fluorescent western blotting. Firstly, we will compare fluorescent and chemiluminescent western blotting. Then, we will learn how infrared fluorescent western blotting can give you truly quantitative and reproducible results. Lastly, we’ll look at the many advantages of fluorescent western blotting, including the possibility to multiplex. Importantly,…

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Molecular Docking: Let the Docking Do the Talking

Want to know whether a lead molecule or a ligand of your choice interacts with a particular protein or a receptor? Do you want this information at your fingertips? All it takes is just a few clicks and key presses on the computer and then out comes a computational prediction. This computational process is also…

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Titering Phage – Counting Something Invisible with Something Only Slightly More Visible

Titering Phage – The Plaque Assay Phage display is a molecular technique used to isolate binding or interaction partners to molecules of interest from an extensive library. Such libraries are often derived from the variable regions of native B-cell antibody-binding genes cloned into phage DNA. A single round of phage display panning involves many important steps. However, the…

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Proteomics and Good Mass Spectrometry Data

It is currently possible to analyze thousands of proteins in a single sample using mass spectrometry (MS) and a database of predicted protein sequences, referred to as ‘bottom-up’ proteomics. With this technology, you can measure protein levels and interactions. Also, you can examine changes in post-translational modifications (PTMs) and isoforms (in an unbiased manner). Working with…

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Benefits of the GUS Gene Reporter System in Plants

Gene reporters enable valuable insight into gene expression. The GUS gene reporter system is one of the popular and common plant reporter systems. GUS,  is short for glucuronidase, an enzyme in the bacterium E. coli. GUS is a good reporter for plants, as it does not occur naturally, and thus, has a low background. With…

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Buffer Banter: Pre-cast PAGE Gels & Buffer Compatibility

This article is not for the die-hard old-school gel runners. You know who you are, the purists, the “I always make my own gels and buffers from scratch” kind. For you we have lots of articles about PAGE gels, both bis-tris and the standard SDS PAGE kind. Instead this article is for the rest of…

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Extracting Better Ubiquitin Data from Your Samples: Beyond the Cellular Skip

The ubiquitin-proteasome system was discovered at the start of the 1980s, and people have been studying it ever since. Initially, researchers thought that tagging a protein with ubiquitin was the cell’s signal for the protein to be scrapped via the proteasome. But more research has shown that, as with all biology, once you’re up close and…

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Examining Cell Interactions with Surface Plasmon Resonance (SPR) and Identifying Epitopes using SPR-Mass Spectrometry (MS)

Surface plasmon resonance (SPR) offers highly efficient, label-free detection for quantifying biomolecular interactions in real-time. Two exciting SPR variants that have sprung up in recent years are SPR for cellular analysis and SPR-mass spectrometry (SPR-MS). SPR for cellular analysis allows you to study how cells attach to different substrates and each other, while SPR-mass spectrometry…

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All Charged Up: The Basics of Ion-Exchange Chromatography

Highly pure proteins are vital for successful experiments; they play roles in research as assay reagents (especially for SPR applications), therapeutic candidates, and of course, as the subjects of structural and biochemical studies.  Chromatography is the science of separation and we utilize it to isolate and purify proteins based on their unique physiochemical properties. One…

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A New Frontier in Protein Quantitation: AlphaLISA

If you ever worked in a biology or biochemistry laboratory, you probably already heard about ELISA. You may have even used it. But do you know what’s behind it? And how you can improve it? Let me guide you through the basics of ELISA, and introduce you to my favorite ELISA technique—AlphaLISA. First Things First… So,…

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How to Scrutinize Your Glycosylated Proteins Without Using Glycosidases

You might have come across protein glycosylation before. Somewhere in the recesses of your memory you might even recall reading something about the protein you’re studying being glycosylated, but what does this mean and how do you analyze it? Glycosylated proteins are molecules decorated with sugar groups as they pass through the ER and Golgi…

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Key Analytical Challenges for Antibody Drug Conjugates

Currently, there are more than 75 antibody drug conjugates (ADCs) in various stages of pre-clinical and clinical development. The combination of a targeted antibody coupled with a cytotoxic small-molecule drug (via  a flexible linker) makes for a lethal and specific oncologic drug product. However, an ADC is a heterogeneous cocktail of molecules with a range…

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Ten Ways to Give Your Surface Plasmon Resonance Experiments a Hand

Surface Plasmon Resonance (SPR) is the gold standard for measuring biomolecular binding without the need for labeling (i.e., label free detection of kinetics). SPR is especially valuable because it doesn’t just provide information at the start and end of a binding event, but can be used to follow association and dissociation kinetics of biomolecules in real-time.…

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Have a BLAST With Your Protein Sequences

When I was being trained in microbiology as an undergrad, one of the first skills I acquired was the ability to quickly compare and visualize amino acid sequences using BLAST and ClustalW. 15 years later, those two programs have done nothing but improve by expanding the data contained in these databases and simplifying the user…

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Stripping Blots – It’s All Fun and Games Until Someone Loses Their Protein

Like all technical fields, molecular biology contains a very robust “theoretical” realm and an equally robust “practical” realm. Unfortunately, these two existences don’t seem to overlap as often as we’d like. Consider, for example, a simple Western blot. While an antibody interacting with its target on a membrane seems pretty straightforward, there are numerous other…

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SDS-PAGE Tips and Tricks to Save You Time

Today, SDS-PAGE is one of the basic methods in biolabs. As a beginner in my lab, I had little help, so my first SDS-PAGE gel took two whole days! Since then, I’ve learned a lot about how to make the process faster. Here are some SDS-PAGE tips and tricks that I learned to help you…

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How to Cherry Pick Your Primary Antibody

How do you pick which antibody you should use in your assay? If you’re starting a new assay and need an antibody for the job, then selecting a new antibody from the plethora available could be high up on your to-do list.

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