An unprecedented binding mode of vitamin B12 in the predicted transporter BtuM

BtuM binds vitamin B12 (cyano-cobalamin) in an unprecedented way. Structural and spectroscopic data indicate that the unusual thiolate coordination allows for chemical modification of the substrate, which is decyanation of the compund. We use mass-spectrometry to show the loss of the 26 Da moiety with various BtuM versions and cyano-cobalamin and dicyano-cobinamide.