Contamination from an affinity column: an encounter with a new villain in the world of membrane-protein crystallization

Small crystals of contaminant protein led to the structure at 1.9 Å resolution of Strep-Tactin in complex with desthiobiotin. Trace amounts of Strep-Tactin were observed to be eluted from a Strep-Tactin column using several detergents, illustrating their possible role in the contamination when crystallizing membrane proteins.