Errasti-Murugarren, EkaitzFort, JoanaBartoccioni, PaolaDíaz, LucíaPardon, ElsCarpena, XavierEspino Guarch, MeritxellZorzano, AntonioZiegler, ChristineSteyaert, JanFernández Recio, JuanFita, IgnacioPalacín Mateo, Manuel2020-04-022020-04-022019Errasti-Murugarren E, Fort J, Bartoccioni P, Díaz L, Pardon E, Carpena X, Espino-Guarch M, Zorzano A, Ziegler C, Steyaert J, Fernández-Recio J, Fita I, Palacín M. L amino acid transporter structure and molecular bases for the asymmetry of substrate interaction. Nat Commun. 2019; 10(1):1807. DOI: 10.1038/s41467-019-09837-z2041-1723http://hdl.handle.net/10230/44149L-amino acid transporters (LATs) play key roles in human physiology and are implicated in several human pathologies. LATs are asymmetric amino acid exchangers where the low apparent affinity cytoplasmic side controls the exchange of substrates with high apparent affinity on the extracellular side. Here, we report the crystal structures of an LAT, the bacterial alanine-serine-cysteine exchanger (BasC), in a non-occluded inward-facing conformation in both apo and substrate-bound states. We crystallized BasC in complex with a nanobody, which blocks the transporter from the intracellular side, thus unveiling the sidedness of the substrate interaction of BasC. Two conserved residues in human LATs, Tyr 236 and Lys 154, are located in equivalent positions to the Na1 and Na2 sites of sodium-dependent APC superfamily transporters. Functional studies and molecular dynamics (MD) calculations reveal that these residues are key for the asymmetric substrate interaction of BasC and in the homologous human transporter Asc-1.application/pdfeng© The Author(s) 2019. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.info:eu-repo/semantics/articlehttp://dx.doi.org/10.1038/s41467-019-09837-zMembrane proteinsX-ray crystallographyinfo:eu-repo/semantics/openAccess