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Archive for the ‘Western blot tutorial series’ Category

Increase Western Blot Throughput with Multiplex Fluorescent Detection

 :: Posted by American Biotechnologist on 01-30-2012

The most common method for analyzing protein expression levels is western blotting with detetion of a single protein target, using horseradish peroxidase-conjugated or alkaline phosphatase-conjugated antibody probes combined with colorimetric or chemiluminescent detection. While these methods work well for studying a single target, they are unsuitable for anlayzing multiple targets at the same time, particularly if the target proteins are of unknown or similar sizes. For analysis of multiple targets, the blot is typically stripped and reprobed for additional targets of interest. Reprobing is time consuming, and often some of the target protein on the blot is lost as a result of the stripping procedure. If one protein is removed to a greater of lesser extent relative to another protein, the ability to quantitate the relative amounts of diffferent proteins of interest is compromised.

In this technical note, you will be introduced to fluorescent western blotting detection which is superior to traditional western blotting when trying to analyze multiple proteins.

Advantages include:

  • fast and quantitative detection of multiple proteins in a single experiment
  • sensitivity compared to chemiluminescent detection
  • linear dynamic range up to 10 times greater than that of chemiluminescent detection
  • fewer experimental steps than chemiluminescent detection
  • no substrate requirement, and therefore no risk of exhausting the substrate and causing a “dead zone” in the blot
  • the ability to visualize and quantitate both phosphorylated and non-phosphorylated forms of individual proteins

The technical note is divided into three sections to help those who are new to fluorescent western blot detection quickly generate reliable and reproducible results.

Click here to download the the technote now!

Three important points about gel equilibration

 :: Posted by American Biotechnologist on 01-19-2012

So you’ve isolated your protein, ran them on a gel and now you’re ready to transfer them to a membrane to begin western blotting. Sounds simple, right? Not so fast. Don’t forget to equilibrate your gel prior to beginning your transfer. Gel equilibration generally involves rinsing the gel in diH2O and soaking it in transfer buffer for approximately 15 min. While it may sound simple, (and it truly is), it is a step that might make the difference between an ugly blot and one that is publication worthy.

Below are some points to consider about gel equilibration:

  1. Gel equilibration removes contaminating electrophoresis buffer salts. If not removed, these salts increase the conductivity of the transfer buffer and the amount of heat generated during transfer.
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  3. Equilibration also allows the gel to adjust to its final size prior to electrophoretic transfer. Gels shrink or swell to various degrees in the transfer buffer depending on the acrylamide percentage and the buffer composition.
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  5. Equilibration is not necessary (i) when the same buffer is used for both electrophoresis and transfer (for example, native gel transfers), or (ii) when using rapid semi-dry transfer systems such as the Trans-Blot® Turbo™ system (consult the user manual for the system you are using).

To learn more tips and tricks, download the Protein Blotting Guide from Bio-Rad Laboartories.

8 critical tips for western blotting analysis

 :: Posted by American Biotechnologist on 01-12-2012

So you think that protein transfer for western blotting is a piece of cake? Consider these important tips before proceeding:

  1. Use only high-quality, analytical grade methanol. Impure methanol can increase transfer buffer conductivity and yield a poor transfer.
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  3. In many cases, ethanol can be substituted for methanol in the transfer buffer with minimal impact on transfer efficiency. Check this using your samples.
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  5. Do not reuse transfer buffer since the buffer will likely lose its ability to maintain a stable pH during transfer.
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  7. Do not dilute transfer buffers below their recommended levels since this decreases their buffering capacity.
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  9. Do not adjust the pH of transfer buffers unless specifically indicated. Adjusting the pH of transfer buffers can result in increased buffer conductivity, manifested by higher initial current output and decreased resistance.
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  11. Increasing SDS in the transfer buffer increases protein transfer from the gel but decreases binding of the protein to nitrocellulose membrane. PVDF membrane can be substituted for nitrocellulose when SDS is used in the transfer buffer.
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  13. Addition of SDS increases the relative current, power, and heating during transfer, and may also affect antigenicity of some proteins.
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  15. Increasing methanol in the transfer buffer decreases protein transfer from the gel and increases binding of the protein to nitrocellulose membrane.

 

To learn more tips and tricks, download the Protein Blotting Guide from Bio-Rad Laboartories.

Transfer Efficiency: Influence of the Gel Structure

 :: Posted by American Biotechnologist on 10-17-2011

With its proprietary transfer buffer, the Trans-Blot Turbo system generates very fast transfer even for high molecular weight proteins. However, as indicated previously, the gel composition, i.e. the acrylamide – bis-acrylamide network density, influences the transfer efficiency. A protein can more easily move out of the gel during the transfer if it is located in a portion of gel that has the widest pore structure. As proteins above 150 kD are always located on the first top part of a gel, the most efficient transfer of those large proteins is achieved when using gradient gel with a concentration of 4% of acrylamide – bis-acrylamide at the top of the gel. The transfer efficiency of proteins from an Any kD homogeneous acrylamide gel and a 4-20% gradient gel is illustrated.

Qualitative transfer efficiency comparison of HMW proteins on homogeneous acrylamide % and gradient gel. Precision Plus Protein™ Unstained standard and E. Coli homogenate (20 μg) were run on both Criterion TGX Any kD Stain-Free and 4-20% gels at 300V for 18 min. The total protein content was detected with the Stain-Free technology using the Gel-Doc EZ imaging system. The gels were then transferred with the Trans-Blot Turbo system with the 7 min preset program using the Trans-Blot Turbo PVDF transfer packs. The total protein content remaining in the gel is detected with the Stain-Free detection, using the same exposure parameters as used with the gels before the transfer for reliable comparison. The content of protein was also detected with the Stain-Free detection on the membrane. Even if most of the proteins are transferred in 7 min, the gradient gel contains less HMW proteins than the homogeneous gel after the transfer.

Protein Transfer: Relationship Between Power Settings and Transfer Times

 :: Posted by American Biotechnologist on 10-16-2011

In theory, increasing the power input and duration of an electrophoretic transfer results in the transfer of more protein out of a gel.

In practice, however, test runs should be used to evaluate transfer efficiency at various field strengths and transfer times for each set of proteins of interest.

The optimum transfer conditions depend on a number of factors, including the size, charge and electrophoretic mobility of the protein, the type of gel and transfer buffer used, and the type of transfer system being used.

In a semi-dry transfer system, the distance between electrodes is determined only by the thickness of the gel-membrane sandwich, and buffering and cooling capacity is limited to the buffer in the filter paper. As a result, the field strength is maximized in semi-dry systems, and the limited buffering and cooling capacity restricts the transfer time. Though power conditions may be varied with the power supply, semi-dry transfers often operate best within a narrow range of settings.