InterPro domain: IPR039421

Proteins in this entry are required for type I protein secretion and have an N-terminal ABC transporter type 1 transmembrane domain and a C-terminal P-loop containing nucleoside triphosphate hydrolase domain. The transmembrane domain forms a pore in the inner membrane and the ATP-binding domain is responsible for energy generation. Sequences are mainly from bacteria, but there are homologues from eukaryotes and archaea. Proteins in this entry include the following:

• Lipid A export ATP-binding/permease protein MsbA, which is required for lipid A and possibly glycerophospholipid transport, and for biogenesis of the outer membrane in bacteria [ 1 ]
• Beta-(1-->2)glucan export ATP-binding/permease protein NdvA from nitrogen-fixing bacteria, which is required for beta-(1-->2)glucan export, essential for nodule formation in legume roots [ 2 ]
• Iron-sulfur clusters transporter ATM1, a yeast mitochondrial protein that exports Fe/S cluster-containing protein precursors and other mitochondrially synthesized proteins to the cytoplasm [ 3 ]. The mammalian equivalents are the ATP-binding cassette sub-family B members 6, 7, 8 and 9, which are required for the transport of heme and porphyrin from the cytoplasm to the mitochondrion [ 4 ]
• Leukotoxin translocation ATP-binding protein LktB, required for leukotoxin export in Mannheimia haemolytica
• Multidrug resistance protein 1, which exports xenobiotics, such as cytotoxic drugs, out of cells leading to tumour cell resistance to multiple drugs [ 5 ]. The bacterial equivalents include multidrug resistance-like ATP-binding protein MdlA
• Alpha-hemolysin translocation ATP-binding protein HlyB from E. coli , a component of the ABC transporter complex HlyBD required for the export of hemolysin [ 6 ]
• Phosphatidylcholine translocator ABCB4, required for lipid secretion in the bile, transporting phosphatidylcholine from the inner to the outer leaflet of the canalicular membrane bilayer into the canaliculi of hepatocytes [ 7 ]
• Bile salt export pump, required for the secretion of bile salts into the canaliculus of hepatocytes [ 8 ]
• Antigen peptide transporter 1, which is required for the transport of antigens from the cytoplasm to the endoplasmic reticulum for association with MHC class I molecules [ 9 ]

1. Function of Escherichia coli MsbA, an essential ABC family transporter, in lipid A and phospholipid biosynthesis. J. Biol. Chem. 273, 12466-75
2. The ndvA gene product of Rhizobium meliloti is required for beta-(1----2)glucan production and has homology to the ATP-binding export protein HlyB. J. Bacteriol. 170, 3523-30
3. The mitochondrial proteins Atm1p and Nfs1p are essential for biogenesis of cytosolic Fe/S proteins. EMBO J. 18, 3981-9
4. Identification of a mammalian mitochondrial porphyrin transporter. Nature 443, 586-9
5. Internal duplication and homology with bacterial transport proteins in the mdr1 (P-glycoprotein) gene from multidrug-resistant human cells. Cell 47, 381-9
6. TolC, an Escherichia coli outer membrane protein required for hemolysin secretion. Proc. Natl. Acad. Sci. U.S.A. 87, 4776-80
7. The human MDR3 P-glycoprotein promotes translocation of phosphatidylcholine through the plasma membrane of fibroblasts from transgenic mice. FEBS Lett. 354, 263-6
8. Mutations and polymorphisms in the bile salt export pump and the multidrug resistance protein 3 associated with drug-induced liver injury. Pharmacogenet. Genomics 17, 47-60
9. Multiple regions of the transporter associated with antigen processing (TAP) contribute to its peptide binding site. J. Immunol. 157, 5467-77