Heteromeric amino acid transporters. In search of the molecular bases of transport cycle mechanisms

Abstract

Heteromeric amino acid transporters (HATs) are relevant targets for structural studies. On the one hand, HATs are involved in inherited and acquired human pathologies. On the other hand, these molecules are the only known examples of solute transporters composed of two subunits (heavy and light) linked by a disulfide bridge. Unfortunately, structural knowledge of HATs is scarce and limited to the atomic structure of the ectodomain of a heavy subunit (human 4F2hc-ED) and distant prokaryotic homologues of the light subunits that share a LeuT-fold. Recent data on human 4F2hc/LAT2 at nanometer resolution revealed 4F2hc-ED positioned on top of the external loops of the light subunit LAT2. Improved resolution of the structure of HATs, combined with conformational studies, is essential to establish the structural bases for light subunit recognition and to evaluate the functional relevance of heavy and light subunit interactions for the amino acid transport cycle.

Disruption of Amino Acid Homeostasis by Novel ASCT2 Inhibitors Involves Multiple Targets

“…In order to understand the potent inhibition of LAT1, we performed molecular docking studies on a homology model of LAT1 based on an alignment with the arginine–agmatine antiporter from E. coli . This transporter is an established model for LAT1 ( Palacin et al, 2016 ) and its structure is available in the outside-open conformation (Protein data bank structure 5J4I; Ilgu et al, 2016 ), which is the relevant conformation for inhibitor binding ( Broer, 2018 ). Several binding poses with similar binding energies were identified, demonstrating a tight fit of the inhibitor to the vestibule and substrate binding site of the outside open transporter ( Figure 4B ).…”

“…A homology model of human LAT1 was built based on the apo outside open conformation (5J4I) of the E. coli arginine–agmatine antiporter ( Ilgu et al, 2016 ) an established prokaryotic model of LAT1 ( Palacin et al, 2016 ). The profile-based alignment was generated using HHpred through the MPI bioinformatics toolkit ( Zimmermann et al, 2017 ).…”

Novel analogs of sulfasalazine as system xc− antiporter inhibitors: Insights from the molecular modeling studies

“…The docked xCT-SSZ complex was placed in the rectangular simulation box and the preassembled bilayers were solvated with TIP3 water molecules. We have not taken into account the heterodimeric structure of Sx c − (Sato, Tamba, Ishii, & Bannai, 1999) because of the experimental data on interactions of xCT with the heavy chain, 4F2 is sparsely available (Palacín, Errasti-Murugarren, & Rosell, 2016). The activation, inactivation, and ion independent mechanism of the receptor are beyond the scope of this study.…”

Consensus mutagenesis approach improves the thermal stability of system xc− transporter, xCT, and enables cryo‐EM analyses

“…The human genome encodes eight SLC7 members (SLC7A5- 11,13), and each specifically associates with either SLC3A1 or SLC3A2. 2,3 The system x c − amino-acid transporter (SLC7A11, also named xCT) is a Na + -independent electroneutral exchange system for cystine/glutamate. 4 This transport system generally uptakes extracellular cystine in exchange for intracellular glutamate, at a 1:1 ratio.…”