Open AccessSubcellular Localization and Topology of the p7 Polypeptide of Hepatitis C Virus
Author(s) -
Séverine Carrère-Kremer,
C. Montpellier-Pala,
Laurence Cocquerel,
Czeslaw Wychowski,
François Pénin,
Jean Dubuisson
Publication year - 2002
Publication title -
journal of virology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.617
H-Index - 292
eISSN - 1070-6321
pISSN - 0022-538X
DOI - 10.1128/jvi.76.8.3720-3730.2002
Subject(s) - ectodomain , biology , membrane topology , epitope , transmembrane protein , transmembrane domain , subcellular localization , membrane protein , glycoprotein , microbiology and biotechnology , integral membrane protein , signal peptide , peptide sequence , c terminus , biochemistry , amino acid , cytoplasm , membrane , antigen , genetics , gene , receptor
Although biological and biochemical data have been accumulated on most hepatitis C virus proteins, the structure and function of the 63-amino-acid p7 polypeptide of this virus have never been investigated. In this work, sequence analyses predicted that p7 contains two transmembrane passages connected by a short hydrophilic segment. The C-terminal transmembrane domain of p7 was predicted to function as a signal sequence, which was confirmed experimentally by analyzing the translocation of a reporter glycoprotein fused at its C terminus. The p7 polypeptide was tagged either with the ectodomain of CD4 or with a Myc epitope to study its membrane integration, its subcellular localization, and its topology. Alkaline extraction studies confirmed that p7 is an integral membrane polypeptide. The CD4-p7 chimera was detected by immunofluorescence on the surface of nonpermeabilized cells, indicating that it is exported to the plasma membrane. However, pulse-chase analyses showed that only approximately 20% of endoglycosidase H-resistant CD4-p7 was detected after long chase times, suggesting that a large proportion of p7 stays in an early compartment of the secretory pathway. Finally, by inserting a Myc epitope in several positions of p7 and analyzing the accessibility of this epitope on the plasma membrane of HepG2 cells, we showed that p7 has a double membrane-spanning topology, with both its N and C termini oriented toward the extracellular environment. Altogether, these data indicate that p7 is a polytopic membrane protein that could have a functional role in several compartments of the secretory pathway.