Streptavidin is a tetrameric protein purified from Streptomyces avidinii. It has wide used in numerous molecular biological protocols dues to its strong affinity for biotin. NWSHPQFEK (Strep tag II) is a nine amino acid peptide with high specificity and affinity towards streptavidin. NWSHPQFEK Tag Antibody is a useful tool in analysis and affinity purification of Strep tag II fusion proteins.