Practice question

Tandem Affinity Purification tag is engineered for sequential, highly specific purification of native complexes under mild conditions. Typical TAP contains Protein A repeats that bind IgG and calmodulin-binding peptide that binds calmodulin resin in calcium-dependent manner, separated by TEV protease site. Calmodulin-binding peptide is the module that interacts with calmodulin-coated beads in second affinity step. ProtA, GST, and His bind IgG, glutathione, and nickel respectively, not calmodulin. This dual orthogonal purification markedly enhances specificity and preserves physiological interactions for downstream mass spectrometry identification with reduced background contaminants.