Recombinant Human TAP protein

**Background of TAP-Tagged Recombinant Proteins**

Tandem Affinity Purification (TAP)-tagged recombinant proteins emerged in the late 1990s as a breakthrough tool for studying protein complexes under near-native conditions. Developed initially in yeast, the TAP system was designed to enable efficient purification of multi-protein assemblies with high specificity while minimizing disruption to cellular interactions. The core innovation lies in the dual-affinity tag fused to the target protein. A typical TAP tag combines two distinct affinity modules—originally Protein A (binding immunoglobulin G) and a calmodulin-binding peptide (CBP)—separated by a cleavage site for the tobacco etch virus (TEV) protease.

The purification process involves two sequential steps. First, the Protein A moiety binds to IgG-coated beads, allowing initial capture of the tagged protein and its interacting partners. After TEV protease cleavage releases the complex, the second purification via CBP-calmodulin interaction further eliminates nonspecific bindings. This two-step strategy significantly enhances purity compared to single-affinity methods.

TAP-tagged systems gained popularity due to their versatility and compatibility with diverse organisms, including mammalian cells. They enabled large-scale interactome studies, revealing dynamic protein networks in processes like transcription, signaling, and metabolism. Moreover, the gentle elution conditions preserved labile interactions and enzymatic activities, making TAP ideal for functional analyses.

Advances in mass spectrometry later synergized with TAP tagging, allowing sensitive identification of co-purified proteins. Despite competition from newer techniques like proximity-dependent biotinylation (e.g., BioID), TAP remains relevant for its balanced specificity and yield, particularly in characterizing stable complexes. Modern variants now incorporate alternative tags (e.g., Strep-tag, FLAG) or inducible expression systems to study context-dependent interactions, sustaining its role in proteomics and structural biology research.