The method or techniques for protein labeling

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Both in vitro and in vivo methods of protein and nucleic acid labeling have been developed to accommodate the need for all types of biomolecular probes.

In vitro Labeling

Chemical methods of protein labeling involve the covalent attachment of the label to amino acids using a label conjugated to chemical groups that react with specific amino acids. These reactive groups, described in detail in the Crosslinker section of the Protein Methods Library, react with specific moieties on distinct amino acids, although a few are also available that nonspecifically react with any amino acid at C-H and N-H bonds. These reactive groups are also used to label nucleic acids.

Enzymatic methods are also used to label both proteins and nucleic acids. These in vitromethods require the respective polymerases, ATP and labeled amino acids or nucleotides. While in vitro DNA transcription is relatively straightforward, the expression of labeled proteins by in vitro translation can be difficult because of the requirement for proper protein length, folding and post-translational modifications that some commercial kits are unable to provide.

In vivo Labeling

Metabolic labeling is a method to label all nucleic acids or proteins in a cell by culturing them with labeled nucleotides or amino acids, respectively. Prolonged cell culture in media containing labeled nucleic acids or amino acids results in all DNA, RNA or proteins becoming labeled via DNA replication, translation and protein turnover. The nucleic acid or protein of interest can then be purified for further experimentation. The benefit of performing metabolic labeling is the consistent labeling of all nucleic acid or protein species. Conversely, metabolic labeling can be toxic, depending on the type of label used, and the number of metabolic labeling reagents is not as broad as those forin vitro methods.