Diagram of a typical ABC transporter protein. (A) A diagram of the structure of a representative ABC protein is shown with a lipid bilayer in yellow, the transmembrane domains in blue, and the nucleotide binding fold in red. Although the most common arrangement is a full-transporter with motifs arranged N-TM-NBF-TM-NBF-C, as shown, NBF-TM-NBF-TM, TM-NBF, and NBF-TM arrangements are also found. (B) The NBF of an ABC gene contains the Walker A and B motifs found in all ATP-binding proteins. In addition, a signature or C motif is also present. The most common amino acids found in these motifs are shown above the diagram; subfamilies often contain characteristic residues in these and other regions.
