One-step purification of the NADH dehydrogenase fragment of the Escherichia coli complex I by means of Strep-tag affinity chromatography.

The proton-pumping NADH:ubiquinone oxidoreductase, also called complex I, is the first energy-transducing complex of many respiratory chains. Complex I of Escherichia coli can be split into three fragments. One of these fragments, the soluble NADH dehydrogenase fragment, represents the electron input part of complex I. It comprises the subunits NuoE, F and G and harbors one flavin mononucleotide and up to six iron-sulfur clusters. Here, we report the one-step purification of this fragment by means of affinity chromatography on StrepTactin. This was achieved by fusing the Strep-tag II peptide to the C-terminus of NuoF or NuoG. Fusion of this peptide to the N-terminus of either NuoE or NuoF disturbed the assembly of the NADH dehydrogenase fragment.