A retention signal necessary and sufficient for endoplasmic reticulum localization maps to the transmembrane domain of hepatitis C virus glycoprotein E2.
The hepatitis C virus (HCV) genome encodes two envelope glycoproteins (E1 and E2). These glycoproteins interact to formin a noncovalent heterodimeric complex which is retained in the endoplasmic reticulum (ER). To identify whether E1 and/or E2 contains an ER-targeting signal potentially involved in ER retention of the E1-E2 complex, these proteins were expressed alone and their intracellular localization was studied. Due to misfolding of E1 in the absence of E2, no conclusion on the localization of its native form could be drawn from the expression of E1 alone. E2 expressed in the absence of E1 was shown to be retained in the ER similarly to E1-E2 complex. Chimeric proteins in which E2 domains were exchanged with corresponding domains of a protein normally transported to the plasma membrane (CD4) were constructed to identify the sequence responsible for its ER retention. The transmembrane domain (TMD) of E2 (C-terminal 29 amino acids) was shown to be sufficient for retention of the ectodomain of CD4 in the ER compartment. Replacement of the E2 TMD by the anchor signal of CD4 or a glycosyl phosphatidylinositol (GPI) moiety led to its expression on the cell surface. In addition, replacement of the E2 TMD by the anchor signal of CD4 or a GPI moiety abolished the formation of E1-E2 complexes. Together, these results suggest that, besides having a role as a membrane anchor, the TMD of E2 is involved in both complex formation and intracellular localization.
Cocquerel
L
L
Equipe Hépatite C, CNRS-UMR 319, Institut de Biologie de Lille et Institut Pasteur de Lille, France.
Meunier
J C
JC
Pillez
A
A
Wychowski
C
C
Dubuisson
J
J
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D015704:CD4 Antigens / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D017261:Glycosylphosphatidylinositols / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D016174:Hepacivirus / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008969:Molecular Sequence Data; D021382:Protein Sorting Signals; D014407:Tumor Cells, Cultured; D014759:Viral Envelope Proteins / Q000235:genetics / Q000378:metabolism*; D015678:Viral Structural Proteins / Q000235:genetics / Q000378:metabolism
D015704:CD4 Antigens; D017261:Glycosylphosphatidylinositols; D021382:Protein Sorting Signals; D014759:Viral Envelope Proteins; D015678:Viral Structural Proteins; C107842:protein E1, Classical swine fever virus; C091015:glycoprotein E2, Hepatitis C virus