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Journal of Virology, June 2001, p. 5584-5592, Vol. 75, No. 12
Laboratoire Rétrovirus et Transfert
Génétique, CNRS URA 1930, Institut Pasteur, 75724 Paris,
France
Received 27 November 2000/Accepted 16 March 2001
PiT-1 and PiT-2 are related multiple transmembrane proteins which
function as sodium-dependent phosphate transporters and as the cell
receptors of several oncoretroviruses. Two copies of a homology domain
that is found in distantly related species assign these proteins to a
large family of phosphate transporters. A current membrane topology
model of PiT-1 and PiT-2 predicts 10 transmembrane domains. However,
the validity of this model has not been addressed experimentally. We
addressed this issue by a comprehensive study of human PiT-2. Evidence
was obtained for glycosylation of asparagine 81. Epitope tagging showed
that the N- and C-terminal extremities are extracellular. The
orientation of C-terminal-truncation mutants expressed in cell-free
translation assays and incorporated into microsomal membranes was
examined by immunoprecipitation. Data were interpreted with respect to previous knowledge about retrovirus binding sites, to the existence of
repeated homology domains, and to predictions made in family members. A
model in which PiT-2 has 12 transmembrane domains and extracellular N-
and C-terminal extremities is proposed. This model, which differs
significantly from previous predictions about PiT-2 topology, may be
useful for further investigations of PiT-2 interactions with other
proteins and for the understanding of PiT-2 transporter and virus
receptor functions.
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.12.5584-5592.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Transmembrane Topology of PiT-2, a Phosphate
Transporter-Retrovirus Receptor
*
Corresponding author. Mailing address: Laboratoire
Rétrovirus et Transfert Génétique, Institut Pasteur,
28 rue du Dr. Roux, 75724 Paris, France. Phone: 33 0 1 45 68 82 46. Fax: 33 0 1 45 68 89 40. E-mail: jmheard{at}pasteur.fr.
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