Protein Detection and Characterization

PROTEIN DETECTION AND CHARACTERIZATION

In molecular biology, it is important to study proteomics, which is the study of proteins and the characteristics of proteins. There are two major ways to identify proteins in biological systems. The first is antibody testing, which is referred to as immunoassays, or mass spectrometry. With immunoassays, it is necessary to have a specific antibody to the protein in order to tag it and identify it.

With antibody detection or immunoassays, antibodies are developed against a specific protein. What this means is that the antibody has specific binding properties affiliated with the protein so that it can bind and tag the protein if it is present in the sample. This is the most common method of detecting proteins. Examples of these types of tests include the ELISA test or enzyme-linked immunoassay test. This test measures the protein levels in the sample. Another is the Western blot test, which requires separation of the protein before detection.

In the ELISA test, specific antibodies bind to the protein. This complex gets acted upon by an enzyme, yielding a product that can be identified chemically by a change in color. The antibodies are fixed to a plastic plate and the serum with the possible protein on it will stick to the plate. If the protein is present, the test will show positivity and a color change. You should know that, in cases like HIV disease, the antigen is fixed to the plate and the HIV antibody is washed over it in order to detect the presence of the antibody, which is itself a protein.

The Western blot test also uses an immunoassay but is more difficult to do. The same principles apply as is seen in the ELISA test; however, the protein is first separated from other antibodies using gel electrophoresis. For HIV disease, this is used as a confirmatory test for HIV disease after the ELISA becomes positive. The HIV testing starts with the ELISA test and is confirmed with the Western Blot test.

There are also protein detection systems that do not require antibodies. They can be used to determine the sequence of a peptide or protein and can detect proteins that do not have a matching antibody available. There is an older technique called the Edman

degradation technique, where the protein is selectively degraded in order to define its sequence.

Mass spectrometry techniques are used after the protein is separated. Proteins are separated using liquid chromatography or gel electrophoresis, which separates proteins out according to their size and electrical charge. The mass spectrometer can analyze the components of the compound. This technique works for non-protein substances as well.