contributed transpoet experimental Gluten-free snack options, writing Aminno manuscript and approving it. Blood — A particular feature of glutamine transporters SNAT3 SLC38A3 and SNAT5 is their ability to retain transport activity, when NaCl is replaced by LiCl Cited by.

Amino acid transport -

Finally, LAT1 and xCT are potential targets for cancer therapy because they are overexpressed in many tumors 13 , Additionally, the crystal structures of the pH-activated sodium-independent amino acid facilitator ApcT and the amino acid transporters AdiC and GadC, distant bacterial homologs of human LATs, which belong to the amino acids, polyamines and organoCations APC family of transporters, have been solved 17 , 18 , 19 , 20 , 21 , Furthermore, the crystal structure of GkApcT, a homolog of the cationic amino acid transporter CAT subfamily, the other subfamily of the SLC7 transporters, has been recently solved All of these bacterial transporters belong to the APC family, within the APC superfamily, and adopt the APC superfamily-fold, originally described for the bacterial transporter LeuT Structural models based on AdiC and ApcT have been used to obtain clues regarding substrate recognition by LAT1 25 and LAT2 16 , BasC crystallizes in complex with a nanobody Nb , in a non-occluded inward-facing conformation in the apo state, and in complex with the substrate analog 2-aminoisobutyrate 2-AIB.

Also, we exploit the structural homology of APC superfamily transporters and the known pathological missense mutations of human LATs to identify key residues involved in transporter function. Our findings reveal the first determinants of the asymmetry of the apparent substrate affinity at the two sides of the plasma membrane in LATs.

BasC was co-crystallized with a newly generated anti-BasC nanobody Nb74 in the absence and presence of the amino acid analog 2-AIB, and the structures were determined to 2.

The BasC-Nb74 complex used for crystallization assays was purified by SEC Supplementary Fig. Data collection and refinement statistics are summarized in Supplementary Table 1.

The apo structure without 2-AIB was solved by molecular replacement and confirmed with data at 4. Crystals of both the apo and holo BasC-Nb74 complex are in space group P4 1 2 1 2, and they contain a single copy of the complex in their asymmetric unit and identical crystal packing.

Supplementary Fig. Crystal structures of BasC. a , b Crystal structure of BasC apo in complex with nanobody 74 Nb74 at 2. Helices are colored blue to red from the N-termini and Nb74 is shown in magenta. c , d Crystal structure of BasC-Nb74 in complex with 2-AIB at 3. Helices are colored as in a , b , and the protein surface is depicted in light gray.

The sagittal plane shows the substrate 2-AIB orange at the end of the vestibule open to the cytoplasm. d Detail of region squared in c showing the residues in the thick barrier that prevents the substrate from accessing the extracellular medium.

BasC contains 12 transmembrane TM helices with the N-termini and C-termini located intracellularly Fig. In addition, the unambiguous alignment with human LATs allowed us to locate all the reported missense mutations in the structure of BasC causing disease Supplementary Fig.

BasC adopts the APC superfamily fold Thus, TM1—TM5 and TM6—TM10 are related by a pseudo two-fold symmetry axis within the plane of the membrane. Both TM1 and TM6 are unwound in the center, forming two discontinuous helices named 1a, 1b, and 6a, 6b Fig.

Two domains can be distinguished in the BasC structure, namely the bundle comprised by TM1, 2, 6, and 7, and the hash domain formed by TM3, 4, 8, and 9, with TM5 and TM10 connecting the two domains at each side of the transporter Fig.

Finally, TM11 and 12 form a V-shape at the external side of TM10 Fig. The apo and holo structures are in an inward cytoplasmic -facing non-occluded conformation with TM1a and TM6b tilted to open a vestibule connecting the center of the transporter with the cytoplasm Fig. By contrast, the central vestibule is not connected to the extracellular space Fig.

Indeed, hydrophobic residues in TM1b Phe 24 , TM3 Ile , TM6a Phe and TM10 Phe , and polar residues in TM1b Lys 25 , extracellular loop 4 Asp , and TM7 Asn and Thr build a thick external gate Fig. Nb74 interacts at the cytoplasmic face of BasC Fig.

BasC not bound to Nb74 was also crystallized and solved at low resolution 7. The BasC-Nb74 interaction interface is formed principally by the complementary determining regions 1 and 3 of the Nb and the BasC intracellular side of TM6b, 8, and 9 and intracellular loops 1 and 4, where mainly polar and electrostatic interactions are present Supplementary Fig.

Nb74 recognizes residues from TM6b in bundle domain and TM8 and TM9 in hash domain Supplementary Fig. The apparent substrate affinity of BasC differs at each side of the membrane e. Nevertheless, insertion of BasC in PLs occurs randomly 3 and addition of Nb74 to the medium blocked only inside-out oriented BasC molecules i.

Indeed, the sidedness of the apparent affinities of the transporter for substrate can be evidenced by using Nb74 in the transport medium to block [ 3 H]L-alanine uptake mediated by the inside-out inserted BasC molecules Fig. Notably, the addition of Nb74 abolished the low apparent affinity component Fig.

These results demonstrate unequivocally that the apparent high affinity component corresponds to the extracellular side of the transporter.

Nb74 reveals the sidedness of the substrate interaction. Because BasC is randomly inserted in proteoliposomes PLs i. normalized to non-treated PLs from 5 to 6 independent experiments. NT non-treated with Nb In the absence of Nb74 black circles , the kinetics is complex without saturation at mM concentrations of extraliposomal l -alanine.

Nb74 magenta circles converts this kinetics in the single component of high apparent affinity corresponding to the extracellular side of BasC. correspond to triplicates.

Source data are provided as a Source Data file. The solved apo BasC structure corresponds to inward facing conformation with the substrate cavity open to the cytoplasmic side, similar to the previously determined apo inward-facing GadC PDB 4DJI 22 Supplementary Fig.

Nevertheless, in contrast to BasC, the GadC structure showed a pH-regulated C-plug domain occupying most of the intracellular vestibule 22 , hindering the identification of potentially relevant gating and substrate-interacting residues.

To define the substrate-binding site of BasC, we crystallized the BasC-Nb74 complex in the presence of 2-AIB. This amino acid analog is a substrate with low apparent affinity intracellular K m Extra electron density was observed in the structure for the bound 2-AIB within the unwound segments of TM1 and TM6 Polder and electron densities are shown in Figs.

This scenario places 2-AIB to the rear of the vestibule, situated approximately in the middle of the plane of the membrane, and with full access to the cytosol Fig.

Structure of the amino acid binding site and substrate-induced fitting. a View of the bound 2-AIB ligand, showing the POLDER electron density map contoured at 3σ, dark red.

Distances between atoms of the substrate and BasC residues compatible with H bonds are indicated dashed lines. c Binding of 2-AIB displaces Gly 19 in the BasC apo structure light gray to H bond distance dashed line with Ser in the holo structure rainbow. Wild-type WT and the indicated homologous mutants of BasC and hAsc-1 were studied.

Transport is normalized to the corresponding wild-type values. from 3 independent experiments are shown. Structural and functional interactions of Tyr normalized to WT values from 3 independent experiments.

The α-carboxyl of 2-AIB forms hydrogen bonds with the N-atoms of TM1 residues Ala 20 and Gly 21, and the α-amino group forms hydrogen bonds with carbonyls of residues Val 17 TM1 , and Phe , Ala and Asp TM6.

In addition, the hydroxyl group of Tyr TM7 is at H-bond distance from the carboxylate group of 2-AIB, and the lateral chain of Phe TM6a occludes substrate interaction with the D-α-methyl group of 2-AIB Fig.

To test whether the α-amino and the α-carboxyl moieties of the substrate are essential requirements, transport of two-carbon molecules lacking either the α-amino or the α-carboxyl group were evaluated.

Moreover, γ-aminobutyrate was not a substrate Fig. This substrate-induced shift brings the O atom of Gly 19 at H-bond distance from the hydroxyl group of Ser TM8 Fig.

In agreement, MD of the holo structure showed that dissociation of the substrate is accompanied by a concomitant relaxation of the TM1 unwound segment that separates Gly 19 and Ser , and reduces the distance between Gly 19 and Asp Supplementary Fig.

Ser is fully conserved among human LATs 3 Supplementary Fig. These results indicate that the interaction of TM1 Gly 19 and TM8 Ser induced by substrate binding is not a requisite for transport function.

In agreement, MD showed that the Gly 19—Ser H-bond is not stable, due to rotamer oscillation of Ser while 2-AIB is in the binding site Supplementary Fig.

Although the recognition of 2-AIB by the cytoplasmic face of the transporter is defined mainly by interactions with backbone atoms of BasC, crystal structures revealed Tyr as a possible substrate interactor Fig. In the apo structure, the hydroxyl group of Tyr is at H-bond distance from the backbone N of Gly 19 TM1 unwound segment and from the backbone O of Ala TM6a Fig.

The displacement of Gly 19 caused by the 2-AIB-induced fit, as seen in the structure of the BasCAIB complex, rearranges the potential H-bonds of the hydroxyl group of Tyr towards the backbone O of Ala , and maintains the carboxyl group of the substrate at H-bond distance Fig.

Of note, Tyr , which is fully conserved among human LATs 3 , sits in the same position as the sodium ion in the sodium-one Na1 site in sodium-dependent APC superfamily transporters, where the cation participates in substrate binding Supplementary Fig.

To question whether the hydroxyl group of Tyr participates in substrate binding in the sodium-independent transporter BasC, we examined the transport function of the YF mutant in reconstituted PLs.

Kinetic characterization of the BasC mutant YF revealed an increased cytoplasmic apparent affinity for l -alanine ~4-fold vs. wild-type BasC , but unaffected extracellular apparent affinity Table 1 , supporting the notion that Tyr participates in the asymmetry of apparent substrate affinity, a characteristic of both BasC and human LATs 3 , 5 , Thermostability-based binding assays 25 , 32 of wild-type BasC and the YF mutant suggested no significant differences in apparent K D values for l -alanine Supplementary Fig.

In agreement, MD indicated that the interaction of Tyr OH with 2-AIB COO is not stable, and in contrast to the stable 2-AIB N —Ala O distance, the distance between the O atoms of Tyr and 2-AIB, rapidly increased from 3.

As Tyr would make a small contribution to substrate binding, the increased cytoplasmic apparent affinity of the YF mutant is likely to be the result of altered transitions during the transport cycle.

As Tyr , located in a position equivalent to the Na1 site of sodium-dependent APC superfamily transporters Supplementary Fig. Sodium binding to the Na2 site is associated with increased substrate binding affinity 33 , The BasC residue Lys TM5 is located in an equivalent position to the Na2 site Fig.

Lys is fully conserved among human LATs and BasC 3. The ε-amino group of Lys points towards the carbonyl group of Gly 15 and the electron density map unambiguously showed the interaction of Lys with Gly 15 at the C-terminal end of TM1a in the holo Fig.

Role of Lys in the asymmetry of the substrate interaction. a Lys forms an H bond with Gly 15 at the C-terminal end of TM 1a in the BasC holo structure. Wild-type WT and the indicated homologous mutants of BasC and human Asc-1 hAsc-1 were studied.

normalized to WT values from 3 independent experiments are shown. Representative kinetic experiments of either extracellular c or cytoplasmic d sides of KA BasC mutant reconstituted in PLs. correspond to quadruplicates. Eadie-Hofstee transformation of the kinetics presented in c and d is shown in the insets.

Kinetic analysis of l -alanine uptake in the BasC KA mutant revealed a dramatic reduction ~fold vs. wild-type of both the extracellular apparent affinity and V max Table 1 , with no impact on the intracellular apparent affinity for l -alanine Fig.

Similarly, mutation KA in hAsc-1 dramatically reduced ~fold vs. wild-type both the external apparent affinity K m values of Overall, these data strongly suggest that this lysine is key for BasC and hAsc-1 function and also for the asymmetric interaction of the substrate at both sides of the transporter, by supporting high apparent affinity of BasC for l -alanine at the extracellular side.

Thus, the KA mutation turns BasC into a more symmetric transporter with apparent K m in the mM or near mM range at both sides of the membrane. Additionally, the highly reduced V max observed in BasC KA and in the homologous mutant KA of hAsc-1 suggests that this lysine also participates in key steps of the transport cycle.

MD gave an unexpected clue as to the role of Lys Unbiased MD of the structure of the BasCAIB complex showed substrate dissociation from the substrate-binding site to simultaneously bind Lys O atom of 2-AIB with the ε-amino group of Lys and Thr 16 N atom of 2-AIB with the backbone O atom of Thr 16 Fig.

These results suggest that 2-AIB-Lys is the first transient interaction of the substrate as it moves to the cytosol. Supporting this hypothesis, thermostability-based binding assays indicated a small but significant reduction in the KA l -alanine binding affinity compared with that of the wild-type Supplementary Fig.

Model for BasC substrate release to the cytoplasm. a 2-AIB orange bound BasC structure PDB ID: 6F2W. Interactions of Lys in TM5 with Gly 15 in TM1a and Tyr in TM7 with Ala in TM6 are shown.

c In the BasC apo structure PDB ID: 6F2G , Gly 19 in the unwound region of TM1 approaches Tyr at hydrogen bond distance. Lys Gly 15 interaction is maintained all along the MD analysis and in both apo and holo structures.

Here we present the structures of a LAT subfamily member BasC in the apo- and holo-form. BasC crystallized in the presence of a nanobody Nb74 that recognizes the intracellular region of the transporter, demonstrating the sidedness of the substrate apparent affinities of the transporter.

The BasC apo and 2-AIB-bound structures in non-occluded inward-facing state offer the first clues on the access and release of the substrate from the cytosol and the substrate-induced fit in LATs. Finally, two fully conserved residues in LATs, namely Tyr TM7 and Lys TM5 in BasC, are responsible for the asymmetry of the apparent affinity of the substrate, a key feature in the physiological role of LATs.

The non-occluded inward-facing conformation structure of BasC in complex with 2-AIB fills a gap in the knowledge of the transport cycle of the APC transporter family 17 , 18 , 19 , 20 , 21 , 22 , 23 , Additionally, structural superimposition of BasC with other APC superfamily transporters in the same conformation, shows that, although similar, differences can be observed, particularly in the tilting of TMs 1a, 5, and 7 Supplementary Fig.

Comparison with the occluded inward-facing structure of the bacterial CAT homolog GkApcT with substrate bound PDB ID 5OQT sheds new light on the access of the substrate from the cytosol. Thus, tilting of TM1a and TM6b, which are more open in BasC non-occluded , and the concomitant dissociation of TM1a from TM5, facilitate access of the substrate from the cytosol to the substrate-binding site and vice versa Fig.

Substrate occlusion in inward-facing SLC7 transporters. a Comparison of the structures of BasC rainbow bound to 2-AIB orange PDB ID: 6F2W in non-occluded state and GkApcT salmon bound to l -alanine cyan PDB ID: 5OQT in occluded state.

Tilting of TM1a and TM6b, together with the accompanying TM7, closes the substrate vestibule to occlude the substrate at the cytoplasmic side arrows. Concomitantly, TM1a interacts and attracts TM5 in the occlusion state arrow.

Only TM1, TM3, TM5, TM6, TM7, and TM8 are depicted for clarity. b Detail of the interactions of K in BasC gray dashed line and K in GkApcT salmon dashed lines in the structures shown in a. Direct interactions of the α-amino and the α-carboxyl moieties of the substrate with the unwound segments of TM1 and TM6 explain the binding of 2-AIB with BasC Figs.

Nevertheless, small differences could be found when compared with other APC-fold transporters. Indeed, in GkApcT, a water molecule connects the substrate with backbone atoms of residues in the unwound segment of TM1 and the hydroxyl group of Tyr TM7.

This suggests a slightly different substrate binding recognition between CAT and LAT subfamilies or a modification of the binding site upon occlusion Additionally, in contrast to AdiC, the α-amino and α-carboxyl moieties of the substrate are a requirement for BasC transport activity 36 Fig.

This feature parallels transport requirements in mammalian LAT1 and LAT2, where the α-amino and the α-carboxyl or a modified carboxyl groups are required for transport 26 , 29 , TM1—TM8 coordination is key for the transport function in APC superfamily transporters.

Similarly, in the sodium-independent APC superfamily transporter CaiT, the Arg side chain in TM5 has been proposed to substitute the function of Na2 by mediating TM1—TM8 coordination during the translocation cycle In this regard, mutations of residues in TM8 involved in TM1—TM8 coordination in APC superfamily transporters result in a strong decrease in both substrate affinity and transporter activity 33 , 34 , In a similar way, mutation of BasC Lys in TM5, a residue lined with the Na2 site Supplementary Fig.

Superimposition of BasC and GkApcT structures Fig. Indeed, the GkApcT electron density map shows an interaction between Lys Lys in BasC and backbone atoms of Gly Ser in BasC , reinforcing the idea that the hydroxyl group of Ser is not essential for transporter activity Fig.

Overall, these results strongly suggest that TM1—TM5 Gly 15—Lys Figs. A physiologically relevant characteristic of LATs is the asymmetry in the apparent substrate affinity at both the intracellular and extracellular sides of the transporter.

This asymmetry allows LAT transporters to control intracellular amino acid pools mM concentrations by exchange with external amino acids µM concentration range 4 , 5. In this context, the interaction of Nb74 with BasC via residues from TM6b in bundle domains and from TM8 and TM9 in hash domains explains the inhibitory effect of Nb74 on BasC transport activity.

Indeed, based on the rocking bundle translocation mechanism proposed for APC superfamily transporters, tilting of the bundle domain over the hash domain rationalizes the major conformational changes in inward-outward facing transitions In this regard, by specifically inhibiting the inside-out BasC molecules in PLs, Nb74 emerges as an excellent tool with which to study the asymmetric substrate interaction of BasC Fig.

Under these conditions, the functionally remaining right-side-out-oriented transporters clearly revealed the high apparent affinity of the extracellular side of BasC for substrates Fig. Binding assays suggest that KA and YF alter the apparent affinity for l -alanine by affecting mainly key steps in the transport cycle that have an impact on the extracellular or cytoplasmic K m values, as previously proposed for the plant Major Facilitator Superfamily nitrate transporter NRT1.

Nevertheless, the molecular bases for these changes are unknown; however, both structural and MD analysis provided several clues. On the one hand, the robust H-bond between BasC residues Tyr and Ala TM6a Fig. In this regard, Tyr , the corresponding residue in AdiC of BasC Tyr , Supplementary Fig.

In fact, the reported asymmetry for agmatine, which lacks the α-carboxyl group, reinforces the idea that, similarly to Tyr in BasC, interaction of Tyr hydroxyl group with substrate α-carboxyl is not essential for the establishment of substrate apparent affinity asymmetry.

Nevertheless, determination of substrate K D at both sides of the transporter will be necessary to define the thermodynamic and kinetic contributions to the decreased intracellular apparent K m of YF mutant. On the other hand, MD trajectories of the BasCAIB complex revealed binding of the substrate to Lys Supplementary Fig.

In this context, the KA mutation significantly reduces l -alanine binding. Nevertheless, the dramatic impact of the KA mutation on extracellular substrate apparent binding affinity and V max suggests that Lys also facilitates the outward-to-inward transition, thereby increasing the apparent affinity for substrates at the extracellular face.

Similarly, mutation of Lys in GkApcT and Lys in ApcT, which are located in the same position as Lys in BasC Supplementary Fig. In summary, we present the crystal structures of a LAT transporter. These structures should enable the building of robust models of human LATs, which in turn can facilitate the generation of specific inhibitors to target transporters of therapeutic interest 45 , 46 , Moreover, the functional characteristics of BasC, in line with those of human LATs, make this transporter a useful model to decipher the molecular mechanisms of LATs and to reveal the molecular defects underlying pathologic mutations in human LATs.

In this regard, the K mutation reported here is a good example of a residue that is mutated in human disease lysinuric protein intolerance and whose underlying molecular defect can be uncovered by the functional and structural study of BasC.

BasC was overexpressed as a C-terminal fusion with GFP in E. coli BL21 Star DE3 cells grown in LB media. Single point mutations Supplementary Table 2 were introduced using the QuikChange site-directed mutagenesis kit Stratagene, San Diego, CA.

All mutations were verified by sequencing. Expression was induced with 0. Next, μl fractions were collected and used for crystallization. To prepare selenomethionine SeMet -labeled BasC protein, E.

SeMet-labeled BasC protein was expressed and purified as for the unlabeled protein. Nanobodies Nbs were prepared against the wild-type BasC protein as described previously coli polar lipid proteoliposomes PLs at a protein to lipid ratio of After one round of panning, clear enrichment was seen for the BasC protein.

Testing for specific BasC protein binding resulted in 29 families. All selections and screenings were done in the absence and presence of l -alanine.

Inducible periplasmic expression of Nbs in E. Surface plasmon resonance Biacore T, GE Healthcare, Chicago, IL was used to screen 29 Nbs one from each family for binding with BasC, purified as for crystallography.

BasC was assayed at —2. The BasC-Nb74 complex rendered the best results initially and consequently crystals were optimized. Purified BasC:Nb74, BasC:NbAIB and SeMet-labeled BasC:Nb74 complexes were concentrated to 1. The film was prepared by dispensing POPC dissolved in CHCl 3 , followed by evaporation of the CHCl 3 using nitrogen gas N 2 at room temperature.

Subsequently, the lipidated protein samples were supplemented with 1. Crystals typically appeared after 4 days, reaching a maximum size after 10—14 days. Special care was taken in data collection to overcome the inherent crystal anisotropy. To this end, crystals were aligned to minimize this effect by using tilted loops and a mini-kappa MK3 with automatic recentering.

The best crystals with and without 2-AIB diffracted up to 3. Complete datasets of SeMet-labeled BasC were obtained up to 4. Data were processed with Xia2 50 using XDS 51 , Aimless and Pointless 52 from the CCP4i suite of programs The Diffraction Anisotropy Server from UCLA was used for anisotropic scaling Phases were obtained by molecular replacement using PHASER 55 and the structures of ApcT PDB ID: 3GIA and GadC 4DJI and a nanobody 5H8D as templates.

Additionally, anomalous data from a modified SeMet protein crystal were collected and methionines were traced in the model. The structure of the NbBasCAIB complex was solved by molecular replacement based on the BasC-Nb74 apo structure. Model building into the electron density map was performed in COOT 56 , with structure refinement carried out in autoBUSTER 57 and REFMAC Polder and Omit maps were calculated with Phenix Images were prepared using Open-Source PyMol The PyMOL Molecular Graphics System, Version 2.

BasC-GFP protein was reconstituted in E. coli polar lipids Sigma-Aldrich, Madrid, Spain , as previously described 3. The suspension was sonicated to clarity and purified BasC protein was added to reach the desired protein to lipid ratio of w:w.

To destabilize the liposomes, 1. This mixture was then incubated at room temperature for the indicated periods. Transport measured in PLs containing no amino acid was subtracted from each data point to calculate the net exchange. Transport values are expressed in pmol of l -alanine per µg of protein and for the indicated time.

BasC protein in PLs was determined by Coomassie blue staining in SDS-PAGE gels compared with known amounts of BasC in DDM micelles, determined by BCA assay Pierce, Rockford, IL and loaded in the same gel. Saturation kinetics were analyzed by nonlinear regression analysis, and the kinetic parameters derived from this method were confirmed by linear regression analysis of the derived Eadie-Hofstee plots.

of three experiments carried out on different days and on different batches of protein and PLs. Melting temperatures T m were determined by fitting the curves to a sigmoidal dose-response equation, as previously described l -alanine concentration.

Binding affinities were determined by fitting the curves to a sigmoidal dose-response equation. The cells were transiently transfected with the N-terminal c-myc tagged hAscpRK5 plasmid a kind gift from Prof. Herman Wolosker; Technion-Israel Institute of Technology using Lipofectamine Invitrogen, Carlsbad, CA.

Single point mutations were introduced using the QuikChange mutagenesis kit. Amino acid uptake measurements were performed on hAsc1-transfected HeLa cells. Uptake rates were measured as previously described Uptake was terminated by washing with an excess volume of chilled transport buffer.

Saturation kinetics was analyzed by nonlinear regression, and the kinetic parameters derived from this method were confirmed by linear regression analysis of the derived Eadie-Hofstee plots. of three experiments performed on different days and on different batches of cells.

The x-ray structure of BasC bound to 2-AIB holo was prepared for molecular dynamics simulations with the Protein Preparation Wizard PrepWizard tool implemented in Schrödinger In this regard, first the nanobody, atomic coordinates of water molecules and other cofactors Zn were removed.

Missing hydrogen atoms were then added by the utility applyhtreat in the PrepWizard tool. PROPKA 3. The resulting structure was subjected to a restrained minimization step with the OPLSAA force field FF , keeping heavy atoms in place and optimizing only the positions of the hydrogen atoms.

edu The protein was then embedded in a POPC lipid bilayer using the CHARMM-GUI Membrane Builder 64 , 65 , 66 , 67 by the replacement method. Next, lipid molecules were placed in the lipid bilayer i. KCl ions corresponding to 0.

In the case of ligand 2-AIB, the automated ligand FF generation procedure CGenFF available in CHARMM-GUI was used to generate the FF parameters Finally, with the CHARMM-GUI Membrane Builder, we also generated the necessary scripts to perform minimization, equilibration and production runs in AMBER, using the CHARMM36 force field C36 FF , as explained below.

After standard Membrane Builder minimization 2. All the experiments were repeated three or more times. Further information on research design is available in the Nature Research Reporting Summary linked to this article. Atomic coordinates for the crystal structures have been deposited in the Protein Data Bank under accession numbers 6F2G WT-Nb74 complex and 6F2W WT-Nb74 2-AIB co-crystal complex.

The source data underlying Figs. Other data are available from the corresponding authors upon reasonable request. Fotiadis, D.

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Bartoccioni, P. Functional characterization of the alanine-serine-cysteine exchanger of Carnobacterium sp AT7. de la Ballina, L. Amino acid transport associated to cluster of differentiation 98 heavy chain CD98hc is at the cross-road of oxidative stress and amino acid availability.

Article Google Scholar. Meier, C. Activation of system L heterodimeric amino acid exchangers by intracellular substrates. EMBO J.

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Impaired amino acid transport at the blood brain barrier is a cause of autism spectrum disorder. Cell , — e18 Guarch, M. Mutations in L-type amino acid transporter-2 support SLC7A8 as a novel gene involved in age-related hearing loss. Elife 7 , pii: e Sakimura, K.

del Amo, E. Pharmacokinetic role of L-type amino acid transporters LAT1 and LAT2. Savaskan, N. XCT modulation in gliomas: relevance to energy metabolism and tumor microenvironment normalization.

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Natl Acad. USA , — Article ADS CAS Google Scholar. Gao, X. Mechanism of substrate recognition and transport by an amino acid antiporter. Nature , — Structure and mechanism of an amino acid antiporter. Science , — Kowalczyk, L. Molecular basis of substrate-induced permeation by an amino acid antiporter.

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Jungnickel, K. Structural basis for amino acid transport by the CAT family of SLC7 transporters. Article ADS Google Scholar. In spite of that, examples of synthetic transporters that can facilitate amino acid transport are rare.

This is mainly because at physiological conditions amino acids predominantly exist as highly polar zwitterions and proper shielding of their charged termini, which is necessary for fast diffusion across lipophilic membranes, requires complex and synthetically challenging heteroditopic receptors.

Here we report the first simple monotopic anion receptor, dithioamide 1 , that efficiently transports a variety of natural amino acids across lipid bilayers at physiological pH. Mechanistic studies revealed that the receptor rapidly transports deprotonated amino acids, even though at pH 7. We also describe a new fluorescent assay for the selective measurement of the transport of deprotonated amino acids into liposomes.

The new assay allowed us to study the pH-dependence of amino acid transport and elucidate the mechanism of transport by 1 , as well as to explain its exceptionally high activity. With the newly developed assay we screened also four other representative examples of monotopic anion transporters, of which two showed promising activity.

Our results imply that heteroditopic receptors are not necessary for achieving high amino acid transport activities and that many of the previously reported anionophores might be active amino acid transporters.

Based on these findings, we propose a new strategy for the development of artificial amino acid transporters with improved properties.

Maslowska-Jarzyna, K. Bąk, B. Zawada and M. Chmielewski, Chem. This article is licensed under a Creative Commons Attribution-NonCommercial 3.

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