Cryo-EM structure of the human heteromeric amino acid transporter bAT-rBAT.

Heteromeric amino acid transporters (HATs) catalyze the transmembrane movement of amino acids, comprising two subunits, a heavy chain and a light chain, linked by a disulfide bridge. The bAT (SLC7A9) is a representative light chain of HATs, forming heterodimer with rBAT, a heavy chain which mediates the membrane trafficking of bAT. The bAT-rBAT complex is an obligatory exchanger, which mediates the influx of cystine and cationic amino acids and the efflux of neutral amino acids in kidney and small intestine. Here, we report the cryo-EM structure of the human bAT-rBAT complex alone and in complex with arginine substrate at resolution of 2.7 and 2.3 Å, respectively. The overall structure of bAT-rBAT exists as a dimer of heterodimer consistent with the previous study. A ligand molecule is bound to the substrate binding pocket, near which an occluded pocket is identified, to which we found that it is important for substrate transport.