Protein Detection in Plants

Now that we are confident we have an accurate sample to test for the presence of the specific protein we are looking for, we can consider different detection methods. Whichever method we choose, it must be sensitive, to detect small amounts of protein, and also specific, to measure only the protein we are interested in. Keep in mind that in GMO testing, our sample will contain many other proteins, often present in very high concentrations, besides just the one transgene protein we are testing for, often present in much lower concentrations. Merely detecting the presence or absence of a protein may not suffice, instead the amount of protein present may need to be measured in some cases such as in our importing country scenerio.

This lesson will focus on an immunoassay known as the ELISA. Immunoassays are an analytical method which use antibodies as reagents to quantitate specific proteins. Figures 3 and 4 show formats of ELISA tests which can measure amounts of proteins present (quantitative). The microwell plate format is more precise in its quantitative estimations than the coated tube format. Figure 5 shows the lateral flow method, which is very quick and easy to conduct. It uses gold-labeled antibodies rather than enzyme catalyzed reactions for detection. However, it is not quantitative, instead only indicates the presence or absence of a protein. The lateral flow format is often used to detect a unique protein encoded by the transgene in a genetically engineered crop plant in the field or grain shipment because it can be done anywhere in a few minutes.

Figure 3 The coated tube ELISA format, which allows visual quantification of proteins.	Figure 4 The microwell plate ELISA format which can be automated and quantitative measurements made.
Figure 5 The quick and easy lateral flow strip method, giving a simple presence/absence detection result.