Streptavidin

Streptavidin is a biotin-binding protein widely used to capture or label biotinylated material. Its tetrameric assembly provides multiple binding sites and can therefore crosslink tagged components. Strong binding makes the pair useful for retention during measurements, but multivalency and steric accessibility affect the resulting geometry. Capture of a biotinylated molecule demonstrates access to the tag, not necessarily preservation of every native molecular interaction. ^[ref]