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2.A.22.6.3
B(O)AT1 or BOAT (SLC6A19; Hartnup's disease protein) is a kidney and intestinal apical membrane epithelial transporter for Na+-dependent, Cl--independent reabsorption of neutral amino acids. Many neutral L-amino acids bind with ~0.5 mM affinities; Leu is the preferred substrate, but all large, neutral, non-aromatic, L-amino acids bind to this transporter. Uptake of leucine is sodium-dependent. In contrast to other members of the neurotransmitter transporter family, this one does not appear to be chloride-dependent.  Activity is enhanced by collectrin (Tmem27), a collecting duct transmembrane (1 TMS) glycoprotein (Q9HBJ8) (Danilczyk et al., 2006). The mouse orthologue is (Q9D687) (Broer et al., 2004; 2008) which is deficient due to mutation(s) in its structural gene, and it forms a complex with collectrin and the brush border carboxypeptidase angiotensin-converting enzyme 2 (ACE2; Q9BYF1). Mutations in Hartnup disorder protein, such as B0AT1(R240Q), decrease complex formation (Kraut and Sachs 2005) and lead to neutral aminoaciduria and in some cases pellagra-like symptoms (Kowalczuk et al., 2008; Singer et al. 2012).  Collectrin is expressed at high levels in the simple embryonic kidney (the pronephros) of amphibians such as Xenopus  (McCoy et al. 2008). ACE2 plays an important role in amino acid transport by acting as a binding partner of SLC6A19 in  the intestine, regulating its trafficking, expression on the cell surface and catalytic activity (Kowalczuk et al. 2008, Camargo et al. 2009). ACE2 is also the cellular receptor for SARS-CoV and SARS-CoV-2 ( causitive agent of COVID-19). Yan et al. 2020 presented cryoEM structures of full-length human ACE2 in the presence of B0AT1 with or without the receptor binding domain (RBD) of the surface spike glycoprotein (S protein) of SARS-CoV-2, both at an overall resolution of 2.9 angstroms. The ACE2-B0AT1 complex is assembled as a dimer of heterodimers, with the collectrin-like domain of ACE2 mediating homodimerization. The RBD is recognized by the extracellular peptidase domain of ACE2 mainly through polar residues (Yan et al. 2020).

Accession Number:Q9D687
Protein Name:Sodium-dependent neutral amino acid transporter B(0) aka B0at1
Length:634
Molecular Weight:71367.00
Species:Mus musculus (Mouse) [10090]
Number of TMSs:12
Location1 / Topology2 / Orientation3: Membrane1 / Multi-pass membrane protein2
Substrate Na+, Cl-, Neutral amino acids

Cross database links:

RefSeq: NP_083154.1   
Entrez Gene ID: 74338   
Pfam: PF00209   
KEGG: mmu:74338   

Gene Ontology

GO:0005887 C:integral to plasma membrane
GO:0005328 F:neurotransmitter:sodium symporter activity
GO:0015175 F:neutral amino acid transmembrane transporte...
GO:0006836 P:neurotransmitter transport
GO:0015804 P:neutral amino acid transport

References (3)

[1] “Molecular cloning of mouse amino acid transport system B(0), a neutral amino acid transporter related to Hartnup disorder.”  Broeer A.et.al.   15044460
[2] “The transcriptional landscape of the mammalian genome.”  Carninci P.et.al.   16141072
[3] “Characterization of mouse amino acid transporter B(0)AT1 (Slc6a19).”  Boehmer C.et.al.   15804236

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Predict TMSs (Predict number of transmembrane segments)
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FASTA formatted sequence
1:	MVRLVLPNPG LEERIPSLDE LEVIEKEEAG SRPKWDNKAQ YMLTCVGFCV GLGNVWRFPY 
61:	LCQSHGGGAF MIPFLILLVF EGIPLLYLEF AIGQRLRKGS MGVWSSIHPA LKGIGIASMF 
121:	VSFMVGLYYN TIIAWVMWYF FNSFQEPLPW SECPLNQNQT GYVEECAKSS SVDYFWYRET 
181:	LNISTSISDS GSIQWWILLC LTCAWSVLYV CIIRGIETTG KAVYITSTLP YVVLTIFLIR 
241:	GLTLKGATNG IVFLFTPNIT ELSNPNTWLD AGAQVFYSFS LAFGGLISFS SYNSVHNNCE 
301:	MDSVIVSVIN GFTSVYAATV VYSIIGFRAT ERFDDCVNTN ILTLINGFDL PEGNVTSENF 
361:	EAYQQWCNAT NPQAYAQLKF QTCDINSFLS EGVEGTGLAF IVFTEAITKM PVSPLWSVLF 
421:	FIMLFCLGLS SMFGNMEGVV VPLQDLNITP KKWPKELLTG LICLGTYLIA FIFTLNSGQY 
481:	WLSLLDSFAG SIPLLIIAFC EMFAVVYVYG VDRFNKDIEF MIGHKPNIFW QVTWRVVSPL 
541:	IMLVIFLFFF VIEVNKTLMY SIWDPNYEEF PKSQKIPYPN WVYAVVVTVA GVPCLSIPCF 
601:	AIYKFIRNCC QKSDDHHGLV NTLSTASVNG DLKN