What feature allows for specific interaction during nickel affinity chromatography with His-tagged GFP?

The specific interaction during nickel affinity chromatography with His-tagged GFP is primarily due to the histidine residues present in the tag. His-tags are short sequences of histidine amino acids that are incorporated into the protein. Nickel ions can bind to the imidazole side chains of histidine, creating a strong interaction. This property is utilized in affinity chromatography, where the His-tagged protein is effectively retained on a nickel-coated resin while other non-tagged proteins are washed away. This allows for a highly selective purification process, enabling the isolation of GFP based on the presence of the His-tag with its unique ability to coordinate with nickel ions.

While other options mention factors like charge, conformation, and molecular weight, they do not specifically relate to the mechanism of interaction occurring in nickel affinity chromatography, which relies fundamentally on the presence of histidine residues in the tag for binding to the nickel ions. Therefore, the correct answer highlights the essential role of the histidine residues in this specific purification technique.