ATP-Binding Cassette Transporter
Transport of specific molecules across the lipid membranes is quite essential when it comes to living organisms. There are numerous transporters that have evolved to carry out most of these functions. ATP-binding cassette transporter [ABC] is the largest transporter gene family that aids perform some of the crucial function in living organisms. ABC transporters are the core members of a protein superfamily made up of one of the largest and oldest families with representatives in extant phyla from prokaryotes to humans.
ATP-binding cassette transporter [ABC transporters] are transmembrane proteins that utilize the energy of the ATP [adenosine triphosphate] binding and hydrolysis to carry out biological processes. These processes include translocation of various substrates across membranes and non-transport-related process such as the translation of DNA and RNA repair. The proteins aid translocate a wide variety of substances that may include sugars, metal ions, amino acids, proteins and peptides and large amounts of hydrophobic compounds.
The ABC transporters genes are quite vital for many processes in the cell and mutation of these genes is harmful. Mutation of the responsible genes can cause or contribute to several human genetic complications that include cystic fibrosis, neurological disease cholesterol and bile transport defects, anemia and drug response. The ABC 
transporters make use of energy of ATP binding and hydrolysis to transport numerous substrates across the cellular membranes.
These transporters are divided into three main functional categories. The prokaryotes, the importers mediate the uptake of nutrients into the cells while the substrates can be transported into amino acids, sugars, peptides and hydrophilic molecules. For the eukaryotes, they do not possess any importers. The exporters or effluxers which are both present in eukaryotes and prokaryotes aid as pumps that push out toxins and drugs available in the cells of living organisms. In the case of gram-negative bacteria, the exporters help transport lipids and polysaccharides from the cytoplasm to the periplasm.
Understanding the mechanism of ATP-binding cassette transporter makes it easy to comprehend how these active transporters can be aid the human cells. These active transporters require energy in the form of ATP to translocate substrates across the cell membranes. These proteins are able to harness the energy of ATP binding or for hydrolysis to drive conformational changes in the transmembrane domain and effectively transport molecules. Alternating-access model is the mechanism that described the conformational changes associated with binding of substrate.
The general mechanism for the transport cycle of the ABC transporters has been fully interpreted. However, the biochemical and structural data has accumulated to support a model through which ATP binding and hydrolysis has been made possible. ATP-binding cassette transporters also aid in the development of multidrug resistance [MDR]. In the MDR, patients who are on medication develop resistance not only to the drug that they are taking but also to several different types of drugs.
Excretion of the drug from the cell b ABC transporters is one of the factors that cause this resistance. Unfortunately, it is not clear how these proteins can translocate many drugs in the cell. ABC transporters are also expressed in the membranes of healthy cells, where they can easily facilitate the transport of numerous endogenous substances as well as substances remote to the body. ABC transporter interactions can be detected through assay types and they are membrane assays and whole based cells allays.
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Refernces
http://en.wikipedia.org/wiki/ATP-binding_cassette_transporter
http://www.jlr.org/content/42/7/1007.full
http://en.wikipedia.org/wiki/ATP-binding_cassette_family