7.6.2.8 ATP + H2O + cobinamide-[cobalamin-binding protein][side 1] - 7.6.2.8 ATP + H2O + cyanocobalamin-[cobalamin-binding protein][side 1] - 7.6.2.8 ATP + H2O + dicyanocobinamide-[cobalamin-binding protein][side 1] - 7.6.2.8 ATP + H2O + vitamin B12-[cobalamin-binding protein][side 1] - 7.6.2.8 ATP + H2O + vitamin B12/out - 7.6.2.8 ATP + H2O + vitamin B12/out BtuCD is a type II ABC importer that catalyzes the translocation of vitamin B12 from the periplasm into the cytoplasm of Escherichia coli. BtuD is complexed with BtuC, a permease protein, and BtuF, a periplasmic binding protein, structure, overview 7.6.2.8 additional information metal-chelate-type ABC transporter HI1470/1 is homologous with vitamin B12 importer BtuCD but exhibits a distinct inward-facing conformation in contrast to the outward-facing conformation of BtuCD. The outward-facing conformation of HI1470/1 is considered to be one of the intermediate states in the translocation cycle of BtuCD 7.6.2.8 additional information BtuCD alone or the BtuCD-F complex do not bind vitamin B12. Only free, uncomplexed BtuF binds vitamin B12 with high affinity. Upon binding of BtuF to BtuCD, vitamin B12 is released from BtuF and is only transiently associated with the complex 7.6.2.8 additional information BtuCD forms a stable complex with the vitamin B12 binding protein BtuF. Using protein docking and MD simulation studies it is shown that holo-BtuF stabilizes the open conformation of BtuCD, whereas the transporter begins to close again when BtuF or vitamin B12 is removed suggesting BtuCD-F is capable of substrate sensitivity. BtuC transmembrane helices 3 and 5, the L-loops and the adjacent helices comprised of BtuC residues 170-180 are identified as hotspots of conformational change 7.6.2.8 additional information BtuCD forms an extremely stable complex with the vitamin B12 binding protein BtuF. Vitamin B12 accelerates complex dissociation rate, with ATP having an additional destabilizing effecf