Which statement best describes the goal of affinity chromatography?

• A. All proteins bind to the resin nonspecifically.
• B. Only nonspecific proteins pass, while the target is always ignored.
• C. The protein of interest is degraded during the process.
• D. Everything passes through except the protein of interest; antibodies bind with their complementary antigenic epitope on the protein of interest and pull it out.

Answer: (D)

Affinity chromatography relies on a highly specific interaction between the protein of interest and a binding partner attached to the resin, such as an antibody recognizing a unique epitope. In this approach, other non-target proteins flow through the column, while the target protein is captured by the immobilized ligand. After washing, the target is eluted under different conditions or with a competing ligand, yielding purified protein.

The statement describes this capture process: everything else passes through, and antibodies bind to their complementary epitope on the protein of interest and pull it out. This captures the essence of immunoaffinity or other ligand-based affinity purification, where the goal is selective enrichment of the target protein rather than nonspecific binding or degradation.