What role does the affinity tag play in protein purification?

The role of the affinity tag in protein purification is significant, and the correct choice emphasizes this function well. Affinity tags are short peptide sequences that are genetically fused to the protein of interest. These tags bind specifically to a corresponding purification matrix or ligand that is attached to a solid support, such as beads or columns used in various chromatography techniques.

This selective binding allows researchers to isolate the tagged protein from a complex mixture of other cellular proteins and contaminants. During the purification process, the sample is passed over a column that contains the immobilized ligand; the tagged protein will bind to it while the unwanted proteins can be washed away. After thorough washing, the specific proteins can be eluted, often using a solution that competes with the tag for binding.

In contrast, while an affinity tag can potentially influence protein solubility or stability indirectly, its primary and most well-defined role is in enabling the selective binding to matrices. The other choices either relate to secondary effects or are not direct roles of the affinity tag itself. Therefore, understanding the primary function of affinity tags helps clarify their importance in protein purification workflows.