Protein Quantification Using the "Rapid Western Blot" Approach.

For the quantification of certain proteins of interest within a complex sample, Western blot analysis is the most widely used method. It enables detection of a target protein based on the use of specific antibodies. However, the whole procedure is often very time-consuming. Nevertheless, with the development of fast blotting systems and further development of immunostaining methods, a reduction of the processing time can be achieved. Major challenges for the reliable protein quantification by Western blotting are adequate data normalization and stable protein detection. Usually, normalization of the target protein signal is performed based on housekeeping proteins (e.g., glyceraldehyde 3-phosphate dehydrogenase, ß-actin) with the assumption that those proteins are expressed constitutively at the same level across experiments. However, several studies have already shown that this is not always the case making this approach suboptimal. Another strategy uses total protein normalization where the abundance of the target protein is related to the total protein amount in each lane. This approach is independent of a single loading control, and precision of quantification and reliability is increased. For Western blotting several detection methods are available, e.g., colorimetric, chemiluminescent, radioactive, fluorescent detection. Conventional colorimetric staining tends to suffer from low sensitivity, limited dynamic range, and low reproducibility. Chemiluminescence-based methods are straightforward, but the detected signal does not linearly correlate to protein abundance (from protein amounts >5μg) and have a relatively narrow dynamic range. Radioactivity is harmful to health. To overcome these limitations, stain-free methods were developed allowing the combination of fluorescent standards and a stain-free fluorescence-based visualization of total protein in gels and after transfer to the membrane. Here, we present a rapid Western blot protocol, which combines fast blotting using the iBlot system and fast immunostaining utilizing ReadyTector all-in-one solution with the Smart Protein Layers (SPL) approach.