What type of chromatographic separation is used in the second purification step for hMPRα?

In the context of protein purification, affinity chromatography is a powerful technique that utilizes specific interactions between a target protein and a ligand that is immobilized on a stationary phase. When a protein mixture is passed through a column containing this stationary phase, only the target protein—such as hMPRα—will bind to the ligand, while other proteins are washed away. After binding, the target protein can be eluted under conditions that disrupt this interaction, allowing for its purification.

This method is particularly advantageous because it leverages the unique properties of the target protein, such as its binding affinity for certain substrates or cofactors, which makes it highly selective and effective for isolating the protein of interest from a complex mixture. In this case, since hMPRα is likely being purified through a mechanism that takes advantage of its affinity for a specific ligand, this step is categorized as affinity chromatography.

The other methods of chromatography mentioned—size exclusion and ion exchange—serve different purposes. Size exclusion separates based on molecular weight, while cation and anion exchange separate based on charge, neither of which would utilize the selective binding nature characteristic of affinity methods.