User:Cboursnell/Sandbox/ABC-3
| ABC-3 | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| File:PDB NULL EBI.jpg | |||||||||
| Identifiers | |||||||||
| Symbol | ABC-3 | ||||||||
| Pfam | PF00950 | ||||||||
| Pfam clan | CL0142 | ||||||||
| InterPro | IPR001626 | ||||||||
| |||||||||
ABC transporters belong to the ATP-Binding Cassette (ABC) superfamily, which uses the hydrolysis of ATP to energise diverse biological systems. ABC transporters minimally consist of two conserved regions: a highly conserved ATP binding cassette (ABC) and a less conserved transmembrane domain (TMD). These can be found on the same protein or on two different ones. Most ABC transporters function as a dimer and therefore are constituted of four domains, two ABC modules and two TMDs.
ABC transporters are involved in the export or import of a wide variety of substrates ranging from small ions to macromolecules. The major function of ABC import systems is to provide essential nutrients to bacteria. They are found only in prokaryotes and their four constitutive domains are usually encoded by independent polypeptides (two ABC proteins and two TMD proteins). Prokaryotic importers require additional extracytoplasmic binding proteins (one or more per systems) for function. In contrast, export systems are involved in the extrusion of noxious substances, the export of extracellular toxins and the targeting of membrane components. They are found in all living organisms and in general the TMD is fused to the ABC module in a variety of combinations. Some eukaryotic exporters encode the four domains on the same polypeptide chain.[1]
The ABC module (approximately two hundred amino acid residues) is known to bind and hydrolyse ATP, thereby coupling transport to ATP hydrolysis in a large number of biological processes. The cassette is duplicated in several subfamilies. Its primary sequence is highly conserved, displaying a typical phosphate-binding loop: Walker A, and a magnesium binding site: Walker B. Besides these two regions, three other conserved motifs are present in the ABC cassette: the switch region which contains a histidine loop, postulated to polarise the attaching water molecule for hydrolysis, the signature conserved motif (LSGGQ) specific to the ABC transporter, and the Q-motif (between Walker A and the signature), which interacts with the gamma phosphate through a water bond. The Walker A, Walker B, Q-loop and switch region form the nucleotide binding site.[2][3][4]
The 3D structure of a monomeric ABC module adopts a stubby L-shape with two distinct arms. ArmI (mainly beta-strand) contains Walker A and Walker B. The important residues for ATP hydrolysis and/or binding are located in the P-loop. The ATP-binding pocket is located at the extremity of armI. The perpendicular armII contains mostly the alpha helical subdomain with the signature motif. It only seems to be required for structural integrity of the ABC module. ArmII is in direct contact with the TMD. The hinge between armI and armII contains both the histidine loop and the Q-loop, making contact with the gamma phosphate of the ATP molecule. ATP hydrolysis leads to a conformational change that could facilitate ADP release. In the dimer the two ABC cassettes contact each other through hydrophobic interactions at the antiparallel beta-sheet of armI by a two-fold axis.[5][6][7][8][9][10]
The ATP-Binding Cassette (ABC) superfamily forms one of the largest of all protein families with a diversity of physiological functions.[1] Several studies have shown that there is a correlation between the functional characterisation and the phylogenetic classification of the ABC cassette.[1][11] More than 50 subfamilies have been described based on a phylogenetic and functional classification,,[1][2] [11]; (for further information see http://www.tcdb.org/tcdb/index.php?tc=3.A.1).
A number of bacterial transport systems have been found to contain integral membrane components that have similar sequences [12]: these systems fit the characteristics of ATP-binding cassette transporters.[13] The proteins form homo- or hetero-oligomeric channels, allowing ATP-mediated transport. Hydropathy analysis of the proteins has revealed the presence of 6 possible transmembrane regions. These proteins belong to family 3 of ABC transporters.
References[edit]
- ^ a b c d Saurin W, Hofnung M, Dassa E (January 1999). "Getting in or out: early segregation between importers and exporters in the evolution of ATP-binding cassette (ABC) transporters". J. Mol. Evol. 48 (1): 22–41. doi:10.1007/pl00006442. PMID 9873074.
{{cite journal}}: CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link) - ^ a b Higgins CF (2001). "ABC transporters: physiology, structure and mechanism--an overview". Res. Microbiol. 152 (3–4): 205–210. doi:10.1016/s0923-2508(01)01193-7. PMID 11421269.
- ^ Higgins CF (1992). "ABC transporters: from microorganisms to man". Annu. Rev. Cell Biol. 8: 67–113. doi:10.1146/annurev.cb.08.110192.000435. PMID 1282354.
- ^ Schneider E, Hunke S (April 1998). "ATP-binding-cassette (ABC) transport systems: functional and structural aspects of the ATP-hydrolyzing subunits/domains". FEMS Microbiol. Rev. 22 (1): 1–20. doi:10.1111/j.1574-6976.1998.tb00358.x. PMID 9640644.
{{cite journal}}: CS1 maint: date and year (link) - ^ Kerr ID (March 2002). "Structure and association of ATP-binding cassette transporter nucleotide-binding domains". Biochim. Biophys. Acta. 1561 (1): 47–64. doi:10.1016/s0304-4157(01)00008-9. PMID 11988180.
{{cite journal}}: CS1 maint: date and year (link) - ^ Karpowich N, Martsinkevich O, Millen L, Yuan YR, Dai PL, MacVey K, Thomas PJ, Hunt JF (July 2001). "Crystal structures of the MJ1267 ATP binding cassette reveal an induced-fit effect at the ATPase active site of an ABC transporter". Structure. 9 (7): 571–586. doi:10.1016/s0969-2126(01)00617-7. PMID 11470432.
{{cite journal}}: CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link) - ^ Yuan YR, Blecker S, Martsinkevich O, Millen L, Thomas PJ, Hunt JF (August 2001). "The crystal structure of the MJ0796 ATP-binding cassette. Implications for the structural consequences of ATP hydrolysis in the active site of an ABC transporter". J. Biol. Chem. 276 (34): 32313–32321. doi:10.1074/jbc.M100758200. PMID 11402022.
{{cite journal}}: CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link) - ^ Hung LW, Wang IX, Nikaido K, Liu PQ, Ames GF, Kim SH (December 1998). "Crystal structure of the ATP-binding subunit of an ABC transporter". Nature. 396 (6712): 703–707. doi:10.1038/25393. PMID 9872322.
{{cite journal}}: CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link) - ^ Diederichs K, Diez J, Greller G, Müller C, Breed J, Schnell C, Vonrhein C, Boos W, Welte W (November 2000). "Crystal structure of MalK, the ATPase subunit of the trehalose/maltose ABC transporter of the archaeon Thermococcus litoralis". EMBO J. 19 (22): 5951–5961. doi:10.1093/emboj/19.22.5951. PMC 305842. PMID 11080142.
{{cite journal}}: CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link) - ^ Gaudet R, Wiley DC (September 2001). "Structure of the ABC ATPase domain of human TAP1, the transporter associated with antigen processing". EMBO J. 20 (17): 4964–4972. doi:10.1093/emboj/20.17.4964. PMC 125601. PMID 11532960.
{{cite journal}}: CS1 maint: date and year (link) - ^ a b Dassa E, Bouige P (2001). "The ABC of ABCS: a phylogenetic and functional classification of ABC systems in living organisms". Res. Microbiol. 152 (3–4): 211–229. doi:10.1016/s0923-2508(01)01194-9. PMID 11421270.
- ^ Reizer J, Reizer A, Saier MH (October 1992). "A new subfamily of bacterial ABC-type transport systems catalyzing export of drugs and carbohydrates". Protein Sci. 1 (10): 1326–1332. doi:10.1002/pro.5560011012. PMC 2142109. PMID 1303751.
{{cite journal}}: CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link) - ^ Frosch M, Edwards U, Bousset K, Krausse B, Weisgerber C (May 1991). "Evidence for a common molecular origin of the capsule gene loci in gram-negative bacteria expressing group II capsular polysaccharides". Mol. Microbiol. 5 (5): 1251–1263. doi:10.1111/j.1365-2958.1991.tb01899.x. PMID 1659649.
{{cite journal}}: CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link)