Fig. 1.

Cryo-EM structure of the b^(0,+)AT1-rBAT transport complex. (A) Cryo-EM density map of the SLC7A9/SLC3A1-encoded neutral and basic amino acid transporter. The b^(0,+)AT1-rBAT complex consists of a heterotetrameric assembly of two rBAT and b^(0,+)AT1 subunits, respectively. (B) Schematic representation of rBAT and b^(0,+)AT1 secondary structure motifs, glycosylation sites, and inter- and intramolecular disulfide bonds. α-Helical and β-sheet elements are shown as cylinders and arrows, respectively. (C) Atomic model of a b^(0,+)AT1-rBAT heterodimer and zoom into distinct interaction sites between the two subunits. b^(0,+)AT1, yellow; rBAT, purple; hydrogen bonds, dashed lines; van der Waals contacts, straight lines. EL: extracellular loop; TM: transmembrane helix. Flexible protein segments that could not be resolved to side-chain level resolution are indicated in light gray.