ATP-binding component of iron-siderophores, vitamin B12 and hemin transporters and related proteins
ABC transporters, involved in the uptake of siderophores, heme, and vitamin B12, are widely conserved in bacteria and archaea. Only very few species lack representatives of the siderophore family transporters. The E. coli BtuCD protein is an ABC transporter mediating vitamin B12 uptake. The two ATP-binding cassettes (BtuD) are in close contact with each other, as are the two membrane-spanning subunits (BtuC); this arrangement is distinct from that observed for the E. coli lipid flippase MsbA. The BtuC subunits provide 20 transmembrane helices grouped around a translocation pathway that is closed to the cytoplasm by a gate region, whereas the dimer arrangement of the BtuD subunits resembles the ATP-bound form of the Rad50 DNA repair enzyme. A prominent cytoplasmic loop of BtuC forms the contact region with the ATP-binding cassette and represent a conserved motif among the ABC transporters.
Jiyao W et al.(2023). "The conserved domain database in 2023.",