Which tag is commonly used in TAP for high-purity complex isolation?
Tandem Affinity Purification relies on Calmodulin Binding Peptide or CBP as second affinity module for high-purity complex isolation under near-physiological conditions. CBP binds calmodulin resin in calcium-dependent manner after first purification on IgG Sepharose and TEV cleavage. Calcium chelation with EGTA allows gentle elution preserving native complexes for downstream mass spectrometry. TRITC is fluorescent dye, biotin requires streptavidin matrix, and GFP is reporter for localization, not an affinity handle in classic TAP design. CBP provides low background and reversible binding essential for sequential purification strategy maximizing purity.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.