Practice question

Pull-down assay is an in vitro affinity capture method to demonstrate protein-protein interactions. Glutathione S-transferase fusion bait protein is expressed recombinantly and immobilized on glutathione conjugated agarose or Sepharose beads. Glutathione, a tripeptide, shows high affinity for GST active site, enabling specific immobilization. When incubated with prey lysate, interacting partners co-precipitate and are eluted for SDS-PAGE or Western blot analysis. Binding to streptavidin, nickel, or biotin represents other tagging systems like biotin-streptavidin or His-tag-Ni-NTA, not relevant to GST-based pull-down methodology.