Summary: Tripartite ATP-independent periplasmic transporters, DctQ component
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Tripartite ATP-independent periplasmic transporter Edit Wikipedia article
|DctP component of Tripartite ATP-independent periplasmic transporter|
|DctQ component of Tripartite ATP-independent periplasmic transporter|
Tripartite ATP-independent periplasmic transporters (TRAP transporters) are a large family of solute transporters found in bacteria and archaea, but not in eukaryotes, that appear to be specific for the uptake of organic acids or related molecules containing a carboxylate or sulfonate group. They are unique in that they utilize a substrate binding protein (SBP) in combination with a secondary transporter.
TRAP transporters were discovered in the laboratory of Prof. David J. Kelly at the University of Sheffield, UK. His group were working on the mechanism used by the photosynthetic bacterium Rhodobacter capsulatus to take up certain dicarboxylic acids. They characterised a binding protein component (DctP) of a transporter that recognized these compounds, which they assumed would form part of a typical ABC transporter, but when they sequenced the genes surrounding dctP they found two other genes encoding integral membrane proteins, dctQ and dctM, but no genes encoding components of an ABC transporter. They further showed that uptake of the same dicarboxylates was independent of ATP and that uptake required an electrochemical ion gradient, making this a unique binding protein-dependent secondary transporter.
Since these early studies, it has become clear that TRAP transporters are present in many bacteria and archaea, with many bacterial having multiple TRAP transporters, some having over 20 different systems.
To date, most substrates for TRAP transporters contain a common feature which is that they are organic acids. This includes C4-dicarboxylates such as succinate, malate and fumarate, keto-acids such as pyruvate and alpha-ketobutyrate and the sugar acid, N-acetyl neuraminic acid (or sialic acid). Other substrates include the compatible solute ectoine and hydroxyectoine and pyroglutamate.
All known TRAP transporters contain 3 protein domains. These are the solute binding protein (the SBP), the small membrane protein domain and the large membrane protein domain. Following the nomenclature for the first characterized TRAP transporter, DctPQM, these subunits are usually named P, Q and M respectively. Around 10% of TRAP transporters have natural genetic fusions between the two membrane protein components, and in the one well studied example of this in the sialic acid specific TRAP transporter from Haemophilus influenzae the fused gene has been named siaQM. The large M subunit is predicted to have 12 transmembrane helices and the small Q subunit to have 4 transmembrane helices and the fused QM proteins are predicted to have 17 transmembrane helices.
By using an SBP, TRAP transporters share some similarity to ABC transporters in that the substrate for the transporter is initially recognized outside of the cytoplasmic membrane. In Gram-negative bacteria, the SBP is usually free in the periplasm and expressed at relatively high levels compared to the membrane domains. In Gram positive bacteria and archaea, the SBP is tethered to the cytoplasmic membrane. In both types of systems the SBP binds to substrate, usually with low micromolar affinity, which causes a significant conformation change in the protein, akin to a Venus flytrap closing. The trapped substrate is then delivered to the membrane domains of the transporter, where the electrochemical ion gradient is somehow exploited to open the SBP, extract the substrate and catalyse its movement across the membrane. For the SiaPQM TRAP transporter which has been studied in a fully reconstituted in vitro form, uptake uses a Na+
gradient and not proton gradient to drive uptake. The SiaPQM systems also exhibits unique properties for a secondary transporter in that it cannot catalyse bidirectional transport as the SBP imposes that movement is only in the direction of uptake into the cell.
Substrate binding protein (SBP)
Following the first structure of a TRAP SBP in 2005, there are now over 10 different structures available. They all have very similar overall structures, with two globular domains linked by a hinge. The substrate binding site is formed by both the domains which enclose the substrate. A highly conserved arginine residue in the TRAP SBPs forms a salt bridge with a carboxylate group on the substrate, which is important for substrate recognition.
There are currently no structures for the membrane domains of any TRAP transporter. It is not even known which subunit(s) made a direct interaction with the SBP subunit during the transport cycle.
- Forward J.A.; Behrendt M.C.; Wyborn N.R.; Cross R.; Kelly D.J. (1997). "TRAP transporters: a new family of periplasmic solute transport systems encoded by the dctPQM genes of Rhodobacter capsulatus and by homologs in diverse gram-negative bacteria". J. Bacteriol. 179 (17): 5482â€“5493. doi:10.1128/jb.179.17.5482-5493.1997. PMCÂ 179420. PMIDÂ 9287004.
- Rabus R.; Jack D.L.; Kelly D.J.; Saier M.H. Jr. (1999). "TRAP transporters: an ancient family of extracytoplasmic solute-receptor-dependent secondary active transporters". Microbiology. 145 (12): 3431â€“3445. doi:10.1099/00221287-145-12-3431. PMIDÂ 10627041.
- Mulligan C.; Kelly D.J.; Thomas G.H. (2007). "Tripartite ATP-independent periplasmic transporters: application of a relational database for genome-wide analysis of transporter gene frequency and organization". J. Mol. Microbiol. Biotechnol. 12 (3â€“4): 218â€“226. doi:10.1159/000099643. PMIDÂ 17587870. S2CIDÂ 30920843.
- Mulligan C.; Fischer M.; Thomas G. (2010). "Tripartite ATP-independent periplasmic (TRAP) transporters in bacteria and archaea". FEMS Microbiol. Rev. 35 (1): 68â€“86. doi:10.1111/j.1574-6976.2010.00236.x. PMIDÂ 20584082.
- Thomas GH, Southworth T, LeÃ³n-Kempis MR, Leech A, Kelly DJ (2006). "Novel ligands for the extracellular solute receptors of two bacterial TRAP transporters". Microbiology. 152 (2): 187â€“198. doi:10.1099/mic.0.28334-0. PMIDÂ 16385129.
- Pernil R, Herrero A, Flores E (2010). "A TRAP transporter for pyruvate and other monocarboxylate 2-oxoacids in the cyanobacterium Anabaena sp. strain PCC 7120". J. Bacteriol. 192 (22): 6089â€“6092. doi:10.1128/JB.00982-10. PMCÂ 2976462. PMIDÂ 20851902.
- Severi E, Randle G, Kivlin P, Whitfield K, Young R, Moxon R, Kelly D, Hood D, Thomas GH (2005). "Sialic acid transport in Haemophilus influenzae is essential for lipopolysaccharide sialylation and serum resistance and is dependent on a novel tripartite ATP-independent periplasmic transporter". Mol. Microbiol. 58 (4): 1173â€“1185. doi:10.1111/j.1365-2958.2005.04901.x. PMIDÂ 16262798. S2CIDÂ 32085592.
- Mulligan C.; Geertsma E.R.; Severi E.; Kelly D.J.; Poolman B.; Thomas G.H. (2009). "The substrate-binding protein imposes directionality on an electrochemical sodium gradient-driven TRAP transporter". Proc. Natl. Acad. Sci. USA. 106 (6): 1778â€“1783. doi:10.1073/pnas.0809979106. PMCÂ 2644114. PMIDÂ 19179287.
- MÃ¼ller A.; Severi E.; Mulligan C.; Watts A.G.; Kelly D.J.; Wilson K.S.; Wilkinson A.J.; Thomas G.H. (2006). "Conservation of structure and mechanism in primary and secondary transporters exemplified by SiaP, a sialic acid binding virulence factor from Haemophilus influenzae" (PDF). J. Biol. Chem. 281 (31): 22212â€“22222. doi:10.1074/jbc.M603463200. PMIDÂ 16702222. S2CIDÂ 37483123.
- Johnston J.W.; Coussens N.P.; Allen S.; Houtman J.C.; Turner K.H.; Zaleski A.; Ramaswamy S.; Gibson B.W.; Apicella M.A. (2008). "Characterization of the N-acetyl-5-neuraminic acid-binding site of the extracytoplasmic solute receptor (SiaP) of nontypeable Haemophilus influenzae strain 2019". J. Biol. Chem. 283 (2): 855â€“865. doi:10.1074/jbc.M706603200. PMIDÂ 17947229.
- Gonin S.; Arnoux P.; Pierru B.; Lavergne J.; Alonso B.; Sabaty M.; Pignol D. (2007). "Crystal structures of an Extracytoplasmic Solute Receptor from a TRAP transporter in its open and closed forms reveal a helix-swapped dimer requiring a cation for alpha-keto acid binding". BMC Struct. Biol. 7: 11. doi:10.1186/1472-6807-7-11. PMCÂ 1839085. PMIDÂ 17362499.
- Fischer M, Zhang QY, Hubbard RE, Thomas GH (2010). "Caught in a TRAP: substrate-binding proteins in secondary transport". Trends Microbiol. 18 (10): 471â€“478. doi:10.1016/j.tim.2010.06.009. PMIDÂ 20656493.
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Tripartite ATP-independent periplasmic transporters, DctQ component Provide feedback
The function of the members of this family is unknown, but DctQ homologues are invariably found in the tripartite ATP-independent periplasmic transporters .
Rabus R, Jack DL, Kelly DJ, Saier MH Jr; , Microbiology 1999;145:3431-3445.: TRAP transporters: an ancient family of extracytoplasmic solute-receptor-dependent secondary active transporters. PUBMED:10627041 EPMC:10627041
Internal database links
|SCOOP:||Abhydrolase_9_N DUF997 LapA_dom|
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR007387
This family consists of DctQ homologues found in TRAP transporters [ PUBMED:10627041 ].
The tripartite ATP-independent periplasmic (TRAP) transporters are substrate-binding protein (SBP)-dependent secondary transporters ubiquitous in prokaryotes, but absent from eukaryotes. They are comprised of an SBP of the DctP or TAXI families and two integral membrane proteins of unequal sizes that form the DctQ and DctM protein families (the small and large membrane components respectively). The TRAP transporter for sialic acid consists of the SBP siaP, and siaQM (termed siaT in some cases), encoding the fused integral membrane protein [ PUBMED:20584082 ].
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|Number in seed:||74|
|Number in full:||19281|
|Average length of the domain:||135.10 aa|
|Average identity of full alignment:||18 %|
|Average coverage of the sequence by the domain:||67.59 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 61295632 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||15|
|Download:||download the raw HMM for this family|
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AlphaFold Structure Predictions
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