ABC-proteins

Holland IB, Kuchler K, Higgins CF (2003) ABC-proteins -from bacteria to man. Academic press... 

The breast cancer resistance protein (BCRP) belongs to the G-branch of the ABC-transporter family (ABCG2). In contrast to most other ABC-proteins, BCRP consists of only one transmembrane domain (TDM) with one nucleotide binding fold (NBF) at its C-terminus. Because of this structural characteristic BCRP as well as other ABC-transporters with only one TMD are termed half transporters. To achieve functional activity these transporters have to form hetero- or homodimers. BCRP is involved in the multidrug resistance of certain tumors and transports endogenous compounds like cholesterol and steroid hormones. 

WOLFGER, H., MamNUN, Y. M., Kuchler, K., Fungal ABC proteins pleiotropic drug resistance, stress response and cellular detoxification, Res. Microbiol. 2001, 152, 375-389. 

The presence at the BBB of members of the multidrug resistance-associated protein (MRPs) family, whose members preferentially transport anionic compounds, is still controversial. The seven members of the MRP family belong, like P-gp, to the ATP-binding cassette (ABC) protein superfamily. Mrpl has been found at the BBB in isolated rat brain capillaries, primary cultures of brain capillary endothelial cells and in immortalized capillary endothelial cells, but not in human brain capillaries [59]. Another member, MRP2 has been found at the luminal membrane of the brain endothelial cells [60]. However, further studies are required to show that there are MRP transporters at the BBB (Figure 15.5). As for P-gp, a functional Mrpl was found in primary cultured rat astrocytes [56] and it has been shown to take part in the release of glutathione disulfide from brain astrocytes under oxidative stress [61]. 

Klein I, Sardaki B, Varadi A (1999) An inventory of the human ABC proteins. Biochim Biophys Acta 1461 237-262. 

Decottignies A, Goffeau A (1997) Complete inventory of the yeast ABC proteins. Nat Genet 15 137-145... 

Specific Drug Transporter Proteins (ABC Proteins MDR Proteins)... 

The NBDs of all ABC proteins are similar in sequence and presumably in three-dimensional structure they are the conserved molecular motor that can be coupled to a wide variety of pumps and channels. When coupled with... 

Pohl A, Devaux PF, Herrmann A. 2005. Function of prokaryotic and eukaryotic ABC proteins in lipid transport. Biochim Biophys Acta 1733 29-52. 

ATP may be released by exocytosis from neurons, where it is co-stored in synaptic vesicles with other neurotransmitters (Bumstock 2004), and from astrocytes (Volknandt 2002). ATP is also released upon stimulation of membrane receptors or upon mechanical stimulation by mechanisms that mainly involve transporters of the ABC protein family or ATP-permeable anion channels (Bodin and Bumstock 2001). Under pathological conditions, massive release of ATP may occur upon damage of the cell membrane or cell lysis. 

These substrate molecules exhibit a wide variety of chemical structures. Some ABC proteins facilitate the transport of inorganic ions, whereas others pump various organic compounds, including lipids, bile acids, glutathione and glucuronide conjugates, or even short peptides. Most ABC family proteins utilize the energy of ATP hydrolysis for this transport activity (active transporters), but some ABC transporters form specific membrane channels. 

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