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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:Q9BYF1
Protein Name:Angiotensin-converting enzyme 2
Length:805
Molecular Weight:92463.00
Species:Homo sapiens (Human) [9606]
Number of TMSs:1
Location1 / Topology2 / Orientation3: Cell membrane1 / Single-pass type I membrane protein2
Substrate Na+, Cl-, Neutral amino acids

Cross database links:

Structure:
1R42   1R4L   2AJF   3D0G   3D0H   3D0I   3KBH   3SCI   3SCJ   3SCK   [...more]

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Predict TMSs (Predict number of transmembrane segments)
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FASTA formatted sequence
1:	MSSSSWLLLS LVAVTAAQST IEEQAKTFLD KFNHEAEDLF YQSSLASWNY NTNITEENVQ 
61:	NMNNAGDKWS AFLKEQSTLA QMYPLQEIQN LTVKLQLQAL QQNGSSVLSE DKSKRLNTIL 
121:	NTMSTIYSTG KVCNPDNPQE CLLLEPGLNE IMANSLDYNE RLWAWESWRS EVGKQLRPLY 
181:	EEYVVLKNEM ARANHYEDYG DYWRGDYEVN GVDGYDYSRG QLIEDVEHTF EEIKPLYEHL 
241:	HAYVRAKLMN AYPSYISPIG CLPAHLLGDM WGRFWTNLYS LTVPFGQKPN IDVTDAMVDQ 
301:	AWDAQRIFKE AEKFFVSVGL PNMTQGFWEN SMLTDPGNVQ KAVCHPTAWD LGKGDFRILM 
361:	CTKVTMDDFL TAHHEMGHIQ YDMAYAAQPF LLRNGANEGF HEAVGEIMSL SAATPKHLKS 
421:	IGLLSPDFQE DNETEINFLL KQALTIVGTL PFTYMLEKWR WMVFKGEIPK DQWMKKWWEM 
481:	KREIVGVVEP VPHDETYCDP ASLFHVSNDY SFIRYYTRTL YQFQFQEALC QAAKHEGPLH 
541:	KCDISNSTEA GQKLFNMLRL GKSEPWTLAL ENVVGAKNMN VRPLLNYFEP LFTWLKDQNK 
601:	NSFVGWSTDW SPYADQSIKV RISLKSALGD KAYEWNDNEM YLFRSSVAYA MRQYFLKVKN 
661:	QMILFGEEDV RVANLKPRIS FNFFVTAPKN VSDIIPRTEV EKAIRMSRSR INDAFRLNDN 
721:	SLEFLGIQPT LGPPNQPPVS IWLIVFGVVM GVIVVGIVIL IFTGIRDRKK KNKARSGENP 
781:	YASIDISKGE NNPGFQNTDD VQTSF