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A structural view onto disease-linked mutations in the human neutral amino acid exchanger ASCT1.

ABSTRACT: The ASCT1 transporter of the SLC1 family is largely involved in equilibration of neutral amino acids' pools across the plasma membrane and plays a prominent role in the transport of both L- and D-isomers of serine, essential for the normal functioning of the central nervous system in mammals. A number of mutations in ASCT1 (E256K, G381R, R457W) have been linked to severe neurodevelopmental disorders, however in the absence of ASCT1 structure it is hard to understand their impact on substrate transport. To ameliorate that we have determined a cryo-EM structure of human ASCT1 at 4.2 Å resolution and performed functional transport assays and molecular dynamics simulations, which revealed that given mutations lead to the diminished transport capability of ASCT1 caused by instability of transporter and impeded transport cycle.

SUBMITTER: Stehantsev P

PROVIDER: S-EPMC8479201 | biostudies-literature | 2021

REPOSITORIES: biostudies-literature

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A structural view onto disease-linked mutations in the human neutral amino acid exchanger ASCT1.

Stehantsev Pavlo P Stetsenko Artem A Nemchinova Mariia M Aduri Nanda Gowtham NG Marrink Siewert J SJ Gati Cornelius C Guskov Albert A

Computational and structural biotechnology journal 20210917

The ASCT1 transporter of the SLC1 family is largely involved in equilibration of neutral amino acids' pools across the plasma membrane and plays a prominent role in the transport of both L- and D-isomers of serine, essential for the normal functioning of the central nervous system in mammals. A number of mutations in ASCT1 (E256K, G381R, R457W) have been linked to severe neurodevelopmental disorders, however in the absence of ASCT1 structure it is hard to understand their impact on substrate tra ...[more]

PMID: 34630942

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Project description:A widely dispersed interference group of retroviruses that includes the feline endogenous virus (RD114), baboon endogenous virus (BaEV), human endogenous virus type W (HERV-W), and type D primate retroviruses uses the human Na(+)-dependent neutral amino acid transporter type 2 (hASCT2; gene name, SLC1A5) as a common cell surface receptor. Although hamster cells are fully resistant to these viruses and murine cells are susceptible only to BaEV and HERV-W pseudotype viruses, these rodent cells both become highly susceptible to all of the viruses after treatment with tunicamycin, an inhibitor of protein N-linked glycosylation. A partial explanation for these results was recently provided by findings that the orthologous murine transporter mASCT2 is inactive as a viral receptor, that a related (ca. 55% identity) murine paralog (mASCT1; gene name, SLC1A4) mediates infections specifically of BaEV and HERV-W, and that N-deglycosylation of mASCT1 activates it as a receptor for all viruses of this interference group. Because the only two N-linked oligosaccharides in mASCT1 occur in the carboxyl-terminal region of extracellular loop 2 (ECL2), it was inferred that this region contributes in an inhibitory manner to infections by RD114 and type D primate viruses. To directly and more thoroughly investigate the receptor active sites, we constructed and analyzed a series of hASCT2/mASCT2 chimeras and site-directed mutants. Our results suggest that a hypervariable sequence of 21 amino acids in the carboxyl-terminal portion of ECL2 plays a critical role in determining the receptor properties of ASCT2 proteins for all viruses in this interference group. In addition, we analyzed the tunicamycin-dependent viral susceptibility of hamster cells. In contrast to mASCT1, which contains two N-linked oligosaccharides that partially restrict viral infections, hamster ASCT1 contains an additional N-linked oligosaccharide clustered close to the others in the carboxyl-terminal region of ECL2. Removal of this N-linked oligosaccharide by mutagenesis enabled hamster ASCT1 to function as a receptor for all viruses of this interference group. These results strongly suggest that combinations of amino acid sequence changes and N-linked oligosaccharides in a critical carboxyl-terminal region of ECL2 control retroviral utilization of both the ASCT1 and ASCT2 receptors.

Project description:B0AT1 (SLC6A19) is a major sodium-coupled neutral amino acid transporter that relies on angiotensin converting enzyme 2 (ACE2) or collectrin for membrane trafficking. Despite its significant role in disorders associated with amino acid metabolism, there is a deficit of comprehensive structure-function understanding of B0AT1 in lipid environment. Herein, we have employed molecular dynamics (MD) simulations to explore the architectural characteristics of B0AT1 in two distinct environments: a simplified POPC bilayer and a complex lipid system replicating the native membrane composition. Notably, our B0AT1 analysis in terms of structural stability and regions of maximum flexibility shows consistency in both the systems with enhanced structural features in the case of complex lipid system. Our findings suggest that diacylglycerol phospholipids significantly alter the pore radius, hydrophobic index, and surface charge distribution of B0AT1, thereby affecting the flexibility of transmembrane helices TM7, TM12, and loop connecting TM7-TM8, crucial for ACE2-B0AT1 interaction. Pro41, Ser190, Arg214, Arg240, Ser413, Pro414, Cys463, and Val582 are among the most prominent lipid binding residues that might influence B0AT1 functionality. We also perceive notable lipid mediated deviation in the degree of tilt and loss of helicity in TM1 and TM6 which might affect the substrate binding sites S1 and S2 in B0AT1. Considerably, destabilization in the structure of B0AT1 in lipid environment was evident upon mutation in TM domain, associated with Hartnup disorder through various structure-based protein stability tools. Our two-tiered approach allowed us to validate the use of POPC as a baseline for initial analyses of SLC transporters. Altogether, our all-atoms MD study provides a platform for future investigations into the structure-function mechanism of B0AT1 in realistic lipid mimetic bilayers and offers a framework for developing new therapeutic agents targeting this transporter.

Dataset Information

A structural view onto disease-linked mutations in the human neutral amino acid exchanger ASCT1.

Publications

A structural view onto disease-linked mutations in the human neutral amino acid exchanger ASCT1.

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