streptavidin

noun

strep·​ta·​vi·​din ˌstrep-ˈtav-əd-ən  -tə-ˈvīd-ᵊn 

: a protein similar to avidin that is produced by a bacterium of the genus Streptomyces (S. avidinii), has four identical subunits that each bind tightly to a molecule of biotin, and is used especially in the detection of molecules (as nucleic acids or antibodies) linked to a biotin label