The Strep-tag protein purification cycle

Images left to right: 1, specific binding of GFP-Strep-tag II fusion protein to Strep-Tactin Sepharose column while unspecific proteins are rapidly washed away with small amounts of physiological buffer; 2, Strep-tag protein is eluted due to addition of the specific competitor "desthiobiotin"; 3 to 5, column regeneration: desthiobiotin is displaced by the yellow solution HABA, which turns red once complexed with Strep-Tactin. HABA is then removed by washing buffer and the column can be re-used.