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Journal of Virology, March 2003, p. 2936-2945, Vol. 77, No. 5
0022-538X/03/$08.00+0 DOI: 10.1128/JVI.77.5.2936-2945.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
N-Linked Glycosylation and Sequence Changes in a Critical Negative Control Region of the ASCT1 and ASCT2 Neutral Amino Acid Transporters Determine Their Retroviral Receptor Functions
Mariana Marin,1 Dimitri Lavillette,1 Sean M. Kelly,1 and David Kabat1*
Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, Oregon 97201-30981
Received 20 August 2002/
Accepted 5 December 2002
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.
* Corresponding author. Mailing address: Department of Biochemistry and Molecular Biology, Oregon Health & Science University, 3181 SW Sam Jackson Park Rd., Mail Code L224, Portland, OR 97201-3098. Phone: (503) 494-8442. Fax (503) 494-8393. E-mail:
kabat {at}ohsu.edu.
Journal of Virology, March 2003, p. 2936-2945, Vol. 77, No. 5
0022-538X/03/$08.00+0 DOI: 10.1128/JVI.77.5.2936-2945.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
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