Protein Conjugation and Labeling

The covalent labeling and conjugation of proteins can be a necessary step in conducting many types of biological experiments. For specific protein detection in immunoassays and bioimaging, purified proteins or target-specific antibodies may be labeled with fluorophores or detection enzymes (such as horseradish peroxidase or alkaline phosphatase). In cellular staining applications, reactive dyes directly bind with extracellular or intracellular proteins to create visible and measurable staining. Another common labeling method is biotinylation, which attaches the small molecule biotin to the target protein. High-affinity binding interactions between biotin and any avidin/streptavidin-conjugated component can thus introduce more applications to the biotinylated protein. Conjugation of immobilized compounds, such as agarose or magnetic beads, offers a means of targeted protein purification. Apart from detection or isolation, proteins may also be conjugated with other compounds to modify biochemical properties. One example is the modification with carrier proteins for immune response. The methods for protein conjugation can be mediated by chemically reactive functional groups (such as maleimide, succinimidyl esters) or via enzymatic reactions. To simplify this process, commercial kits, reagents, and services are available, offering many options in both the conjugate and method of labeling.