2.A.3.8.19
B(0,+)-type amino acid transporter 1 (B(0,+)AT) (Glycoprotein-associated amino acid transporter b0,+AT1) (Solute carrier family 7 member 9).  The cryo-EM structure of the human heteromeric amino acid transporter b(0,+)AT-rBAT complex has been solved (Yan et al. 2020). The two subunits, a heavy chain and a light chain are linked by a disulfide bridge. The light chain forms a heterodimer with rBAT, a heavy chain which mediates the membrane trafficking of b(0,+)AT. The b(0,+)AT-rBAT complex is an obligatory exchanger, which mediates the influx of cystine and cationic amino acids and the efflux of neutral amino acids in the kidney and small intestine. Yan et al. 2020 reported the cryo-EM structure of the human b(0,+)AT-rBAT complex alone and in complex with an arginine substrate at resolutions of 2.7 and 2.3 Å, respectively. The overall structure is a dimer of heterodimers. Arg is bound to the substrate binding site in an occluded pocket. The cryoEM structure reveals a heterotetrameric protein assembly composed of two heavy and two light chain subunits, respectively. The  interaction between the two units is mediated by dimerization of the heavy chain subunits and does not include participation of the light chain subunits (Wu et al. 2020). The b((0,+))AT1 transporter adopts a LeuT fold and is in an inward-facing conformation. An amino-acid-binding pocket is formed by transmembrane helices 1, 6, and 10 and is conserved among SLC7 transporters.