Total protein staining provides an image of the protein migration pattern in a gel or on a blot. This information helps determine transfer efficiency and the molecular weight, relative quantity, and other properties of the transferred proteins. This section provides an overview of total protein stains, including anionic dyes (such as amido black, Coomassie blue, Ponceau S, and Fast Green), fluorescent stains, and colloidal gold stains and discusses the advantages and disadvantages of these stains. It also provides protocols for total protein staining and troubleshooting tips for various problems in staining procedures.
Related Topics: Immunodetection.
When performing total protein blot staining, note that:
Total protein detection. Blot stained with SYPRO Ruby blot stain showing the total protein pattern of an E.coli lysate containing an over-expressed GST fusion protein on the blot.
Comparison of total protein staining methods.
The first techniques developed for total protein staining of blotted membranes used the same anionic dyes commonly used for staining proteins in polyacrylamide gels. These dyes include amido black (Towbin et al. 1979), Coomassie (Brilliant) Blue R-250 (Burnette 1981), Ponceau S, and Fast Green FCF (Reinheart and Malamud 1982). Of these:
Amido Black — destains rapidly in acetic acid/isopropanol solution and produces very little background staining. Amido black may interfere with downstream immunodetection.
Coomassie Brilliant Blue — may show high background staining, even after long destaining procedures, and is not compatible with subsequent immunodetection.
Ponceau S and Fast Green — are compatible with downstream immunodetection methods, and Fast Green can be easily removed after visualization to allow subsequent immunological probing.
These dyes are easy to prepare and they stain proteins quickly, but they are relatively insensitive when compared to other stains (see table above).
Fluorescent stains such as SYPRO Ruby and Deep Purple provide highly sensitive detection of proteins on blots as well as in gels. SYPRO Ruby blot stain allows detection as low as 2 ng. After staining, target proteins can be detected by colorimetric or chemiluminescence immunodetection methods, or analyzed by microsequencing or mass spectrometry with no interference from the protein stain.
You can visualize proteins separated by gel electrophoresis using various staining procedures or stain-free technology. Select visualization techniques based on the capabilities of the imaging equipment used in your lab and the demands of your applications.
Colloidal gold is an alternative to anionic dyes that provides detection sensitivities rivaling those of immunological detection methods (Moeremans et al. 1987, Rohringer and Holden 1985). When a solution of colloidal gold particles is incubated with proteins bound to a nitrocellulose or PVDF membrane, the gold binds to the proteins through electrostatic adsorption. The resulting gold-protein complex produces a transient, reddish-pink color due to the optical properties of colloidal gold. This gold-protein interaction is the basis for total protein staining with colloidal gold as well as for specific, immunogold detection (see Immunogold Labeling)
Burnette WN (1981). "Western blotting": electrophoretic transfer of proteins from sodium dodecyl sulfate-polyacrylamide gels to unmodified nitrocellulose and radiographic detection with antibody and radioiodinated protein A. Anal Biochem 112, 195–203.
Moeremans M et al. (1987). The use of colloidal metal particles in protein blotting. Electrophoresis 8, 403–409.
Reinhart MP and Malamud D (1982). Protein transfer from isoelectric focusing gels: the native blot. Anal Biochem 123, 229–235.
Rohringer R and Holden DW (1985). Protein blotting: detection of proteins with colloidal gold, and of glycoproteins and lectins with biotin-conjugated and enzyme probes. Anal Biochem 144, 118–127.
Towbin H et al. (1979). Electrophoretic transfer of proteins from polyacrylamide gels to nitrocellulose sheets: procedure and some applications. Proc Natl Acad Sci USA 76, 4350–4354.
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