Identification of a Dps contamination in Mitomycin-C–induced expression of Colicin Ia

Colicins are bacterial toxins targeting Gram-negative bacteria, including E. coli and related Enterobacteriaceae strains. Some colicins form ion-gated pores in the inner membrane of attacked bacteria that lethal to their target. Colicin Ia was first pore-forming toxin, for which a high-resolution structure monomeric full-length protein determined. It is so far also only colicin, low-resolution its membrane-inserted pore reported by negative-stain electron microscopy. Resolving this at atomic level would allow an understanding mechanism toxin formation. Here, we report observation made during attempt determine resolution. natively expressed mitomycin-C induction under native SOS promotor purified following published protocols. The visual appearance microscope negatively stained preparations lattice parameters 2D crystals obtained from material were highly similar those earlier resulting same purification protocol. However, higher-resolution structural analysis revealed Dps (DNA-binding starved cells), dodecameric protein. This finding suggests previously “Colicin oligomeric pore” actually shows Dps. • cells induced with mitomycin C. samples contained as impurity. strongly resembles form. Previously data using protocol should be considered care.