Proteins are composed of polypeptide chains and their biological functions are determined in part by the correct folding, size, and the number of reactive functional groups present throughout the polypeptide chain. The ability to provide site-specific protein modifications provides researchers with the ability to investigate a wide range of properties and their overall biological function. Protein labeling and modifications technologies include adding fluorophores, biotin, and other small molecules to examine protein-protein interactions, protein folding, to investigate the overall protein structure, and their biological function.
The discovery and wide-spread incorporation of green fluorescent protein (GFP) is a powerful example of this technology. GFP and its counterpart molecules have had an enormous impact on numerous fields of study and our understanding of biological processes. For example, the incorporation of fluorescent tags onto antibodies allows for the detection and quantification of highly specific protein complexes in tissues or the directional immobilization of antibody-protein complexes for ELISA and western blot applications. However, a significant disadvantage of using GFP is that the protein function may be disrupted by the incorporation of additional protein tags of this size. To circumvent this challenge, researchers may use smaller fluorescent tags compared to a GFP, biotin, or incorporate non-natural amino acids that contain biorthogonal functionality.
The incorporation of unique enzymes or probes is another method used by researchers to label proteins. Commonly used enzyme-protein conjugations include alkaline phosphatase (AP), and horseradish peroxidase (HRP). There are numerous advantages for using enzyme-protein labeling technologies as they allow for signal amplification, diverse signal outputs, and there are numerous substrates available for each enzyme. Common signal outputs include fluorescent, chemiluminescent, or colorimetric detection. The variety of these signal outputs make them suitable for immunohistochemistry (IHC) or immunofluorescent (IF)-based detection applications in cells and tissues.
In the field of disease research and drug discovery, targeted protein degradation technology is being intensely studied by researchers to identify novel drug targets and potential therapeutics. Proteolysis-targeting chimeras technology utilizes bifunctional molecules that are designed on one end to bind to a target disease protein, while the other end binds to an E3 ligase to eliminate the protein from the cell. The combined specificity of these molecules to a wide range of disease targets and their ability to target them for protein degradation using internal cellular protein degradation systems make them a powerful protein labeling technology for disease research.