Fig. 1: BtuG2 has a beta propeller fold which binds corrinoids.
a Diagrams showing the structures of the corrinoids used for crystallography. Lower ligand is depicted in light blue in the “base-on” conformation. Side chains of the corrin ring are labelled with letters in red. b Genetic organisation of the B12 transport system in E. coli (btuBFCD) and the three homologous loci in B. theta, showing the locations of BtuB (yellow), BtuG (blue) and BtuH proteins (pink), notice that BtuG1 has a BtuH domain fused. The pink triangles represent B12-dependent riboswitches and the black lollipops transcription terminators. The inner membrane ABC transporters are in green. c SDS gel showing faint pink bands, indicated with an asterisk on the left panel, corresponding to CNCbl. The boiled sample also shows a minor lower mobility band (~15% of the sample) which corresponds to the fraction of BtuG2 that has lost CNCbl after boiling. The right panel shows the same gel after Coomassie staining (B, boiled; NB, non-boiled). Gels are representative of three independent replicates, uncropped gels in Source Data. d Cartoon representation of BtuG2 (in rainbow colour, N terminus in blue) bound to CNCbl (magenta). Note that the lower ligand is pointing outwards (right panel). e Close-up of the residues forming hydrogen bonds (black dashed lines) with CNCbl.
