Summary: BCCT, betaine/carnitine/choline family transporter
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Betaine transporter Edit Wikipedia article
|BCCT family transporter|
Proteins of the Betaine/Carnitine/Choline Transporter (BCCT) family are found in Gram-negative and Gram-positive bacteria and archaea. The BCCT family is a member a large group of secondary transporters, the APC superfamily. Their common functional feature is that they all transport molecules with a quaternary ammonium group [R-N (CH3)3]. The BCCT family proteins vary in length between 481 and 706 amino acyl residues and possess 12 putative transmembrane Î±-helical spanners (TMSs). The x-ray structures reveal two 5 TMS repeats with the total number of TMSs being 10. These porters catalyze bidirectional uniport or are energized by pmf-driven or smf-driven proton or sodium ion symport, respectively, or else by substrate:substrate antiport. Some of these permeases exhibit osmosensory and osmoregulatory properties inherent to their polypeptide chains.
The structures of the sodium-independent carnitine/butyrobetaine antiporter CaiT from Proteus mirabilis (PmCaiT) (â€‹) and from E. coli (EcCaiT)( â€‹) were determined.
Most members of the BCCT family are Na+- or H+-dependent, whereas EcCaiT is a Na+- and H+-independent substrate:product antiporter. The three-dimensional architecture of CaiT resembles that of the Na+-dependent transporters LeuT and BetP, but in CaiT, a methionine sulphur takes the place of the Na+ to coordinate the substrate in the central transport site, accounting for Na+ independence. Both CaiT structures ( â€‹, â€‹) show the fully open, inward-facing conformation, and thus complete the set of functional states that describe the alternating access mechanism. EcCaiT ( â€‹, â€‹) contains two bound butyrobetaine substrate molecules, one in the central transport site, the other in an extracellular binding pocket. In the structure of PmCaiT, a tryptophan side chain occupies the transport site, and access to the extracellular site is blocked. Binding of both substrates to CaiT reconstituted into proteoliposomes is cooperative, with Hill coefficients of up to 1.7, indicating that the extracellular site is regulatory. Schulze et al. (2010) proposed a mechanism whereby the occupied regulatory site increases the binding affinity of the transport site and initiates substrate translocation. Glycine betaine transporters have been found to contain a conserved region with four tryptophans in their central region.
Most secondary-active transporters transport their substrates using an electrochemical ion gradient, but the carnitine transporter (CaiT) is an ion-independent, L-carnitine/gamma-butyrobetaine antiporter. Crystal structures of CaiT from E. coli and Proteus mirabilis revealed the inverted five-transmembrane-helix repeat similar to that in the amino acid/Na+ symporter, LeuT. Kalayil et al. (2013) showed that mutations of arginine 262 (R262) made CaiT Na+-dependent with increased transport activity in the presence of a membrane potential, in agreement with substrate/Na+ cotransport. R262 also plays a role in substrate binding by stabilizing the partly unwound TM1' helix.
Modeling CaiT from P. mirabilis in the outward-open and closed states on the corresponding structures of the related symporter BetP revealed alternating orientations of the buried R262 side chain, which mimic sodium binding and unbinding in the Na+-coupled substrate symporters. A similar mechanism may be operative in other Na+/H+-independent transporters, in which a positively charged amino acid replaces the cotransported cation. The oscillation of the R262 side chain in CaiT indicates how a positive charge triggers the change between outward-open and inward-open conformations.
The generalized transport reactions catalyzed by members of the BCCT family are:
- Substrate (out) + nH+ (out) â†’ Substrate (in) + nH+ (in)
- Substrate (out) + Na+ (out) â†’ Substrate (in) + Na+ (in)
- Substrate-1 (out) + Substrate-2 (in) â†’ Substrate-1 (in) + Substrate-2 (out)
- Substrate (out) â‡Œ Substrate (in)
- Substrate = a quaternary amine
Other betaine transporters
- The mammalian betaine transporter: Sodium- and chloride-dependent betaine transporter
- Saier, MH Jr. "2.A.15 The Betaine/Carnitine/Choline Transporter (BCCT) Family". Transporter Classification Database. Saier Lab Bioinformatics Group.
- Schulze, S; KÃ¶ster, S; Geldmacher, U; Terwisscha van Scheltinga, AC; KÃ¼hlbrandt, W (September 9, 2010). "Structural basis of Na(+)-independent and cooperative substrate/product antiport in CaiT" (PDF). Nature. 467 (7312): 233â€“6. Bibcode:2010Natur.467..233S. doi:10.1038/nature09310. PMIDÂ 20829798. S2CIDÂ 4341977.
- Kempf B, Bremer E, Kappes RM (1996). "Three transport systems for the osmoprotectant glycine betaine operate in Bacillus subtilis: characterization of OpuD". J. Bacteriol. 178 (17): 5071â€“5079. doi:10.1128/jb.178.17.5071-5079.1996. PMCÂ 178300. PMIDÂ 8752321.
- Kalayil, S; Schulze, S; KÃ¼hlbrandt, W (October 22, 2013). "Arginine oscillation explains Na+ independence in the substrate/product antiporter CaiT". Proc. Natl. Acad. Sci. U.S.A. 110 (43): 17296â€“301. Bibcode:2013PNAS..11017296K. doi:10.1073/pnas.1309071110. PMCÂ 3808595. PMIDÂ 24101465.
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BCCT, betaine/carnitine/choline family transporter Provide feedback
No Pfam abstract.
Jung H, Buchholz M, Clausen J, Nietschke M, Revermann A, Schmid R, Jung K;, J Biol Chem. 2002;277:39251-39258. : CaiT of Escherichia coli, a new transporter catalyzing L-carnitine/gamma -butyrobetaine exchange. PUBMED:12163501 EPMC:12163501
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR000060
These prokaryotic transport proteins belong to a family known as BCCT (for Betaine/Carnitine/Choline Transporters) [ PUBMED:20923416 ] and are specific for compounds containing a quaternary nitrogen atom. The BCCT proteins contain 12 transmembrane regions and are energised by proton symport. They contain a conserved region with four tryptophans in their central region [ PUBMED:8752321 ].
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Cellular component||membrane (GO:0016020)|
|Molecular function||transmembrane transporter activity (GO:0022857)|
|Biological process||nitrogen compound transport (GO:0071705)|
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This large superfamily contains a variety of transporters including amino acid permeases that according to TCDB belong to the APC (Amino acid-Polyamine-organoCation) superfamily.
The clan contains the following 21 members:AA_permease AA_permease_2 AA_permease_C Aa_trans BCCT BenE Branch_AA_trans CstA DUF3360 HCO3_cotransp K_trans MFS_MOT1 Na_Ala_symp Nramp SNF Spore_permease SSF Sulfate_transp Transp_cyt_pur Trp_Tyr_perm Xan_ur_permease
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1Cannot generate PP/Heatmap alignments for seeds; no PP data available
Key: available, not generated, — not available.
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|Author:||Mian N , Bateman A|
|Number in seed:||77|
|Number in full:||7172|
|Average length of the domain:||470.40 aa|
|Average identity of full alignment:||35 %|
|Average coverage of the sequence by the domain:||86.16 %|
|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:||20|
|Download:||download the raw HMM for this family|
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The tree shows the occurrence of this domain across different species. More...
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For all of the domain matches in a full alignment, we count the number that are found on all sequences in the alignment. This total is shown in the purple box.
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For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the BCCT domain has been found. There are 24 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein sequence.
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AlphaFold Structure Predictions
The list of proteins below match this family and have AlphaFold predicted structures. Click on the protein accession to view the predicted structure.