ABC transporter: Difference between revisions

'''A'''TP '''B'''inding '''C'''assette (ABC) '''[[Transporters]]''' are ATP-dependent membrane proteins critical for most aspects of cell physiology, including the uptake of nutrients (importers) and elimination of waste products and energy generation (exporters) which are predominantly expressed in excretory organs, such as the liver, intestine, blood-brain barrier, blood-testes barrier, placenta, and kidney<ref name="Kidney"/><ref name="FourDomainsABCT"/>. There are many ABC Transporters in organisms, for instance, there are 28 in Saccharomyces,58 in Caenorhabditis, 51 in Drosophila,129 in Arabadopsis,and the 69 ABC transporters in E. coli account for almost 5% of its genomic coding capacity<ref name="EColi"/>. ABC transporter protein translocates substrates across membranes.  It contains a Solute Binding Domain (SBD).  CFTR (Cystic Fibrosis Transmembrane Regulator)  translocates chloride and  thiocyanate.  It contains a nucleotide binding domain (NBD).  Mutations in CFTR lead to Cystic Fibrosis. In humans the ABC transporters are classified into subfamilies, i.e. ABCB6 is ABC subfamily B member 6. The images at the left and at the right correspond to one representative ABC transporter, ''i.e.'' the crystal structure of B12 Bacterial ABC Transporter ([[1l7v]]).

To achieve export, ABC transporters require a minimum of four domains. Two transmembrane domains (TMDs) form the ligand binding sites and provide specificity, and two NBDs bind and hydrolyze ATP to drive the trans-location of the bound ligand. The NBDs, but not the TMDs, are homologous throughout the family and have several characteristic motifs including the Walker A and B motifs common to many nucleotide binding proteins and others like the ABC signature, stacking aromatic D, H, and Q loops, which are unique to the family<ref name="FourDomainsABCT"/>.

== 3D Structures of ABC transporter ==