Charged Residues in the Transmembrane Domains of Hepatitis C Virus Glycoproteins Play a Major Role in the Processing, Subcellular Localization, and Assembly of These Envelope Proteins

Abstract

For most membrane proteins, the transmembrane domain (TMD) is more than just an anchor to the membrane. The TMDs of hepatitis C virus (HCV) envelope proteins E1 and E2 are extreme examples of the multifunctionality of such membrane-spanning sequences. Indeed, they possess a signal sequence function in their C-terminal half, play a major role in endoplasmic reticulum localization of E1 and E2, and are potentially involved in the assembly of these envelope proteins. These multiple functions are supposed to be essential for the formation of the viral envelope. As for the other viruses of the family Flaviviridae, these anchor domains are composed of two stretches of hydrophobic residues separated by a short segment containing at least one fully conserved charged residue. Replacement of these charged residues by an alanine in HCV envelope proteins led to an alteration of all of the functions performed by their TMDs, indicating that these functions are tightly linked together. These data suggest that the charged residues of the TMDs of HCV glycoproteins play a key role in the formation of the viral envelope.

Identification of a dominant endoplasmic reticulum-retention signal in yellow fever virus pre-membrane protein

“…As a result of good conservation in the organization of the transmembrane domains in prM and E of members of the genus Flavivirus (Cocquerel et al, 2000), ER-retention signals, similar to those characterized in this work, are likely to be present in the other flaviviruses. However, differences in the strength of such signals can exist, as highlighted recently (Hsieh et al, 2008).…”

“…Together, these data indicate that TM2 of prM also contains an ER-retention function. (Cocquerel et al, 2000) is highlighted in grey. Mutated TM2 (TM2prM (AL)3 ) had the sequence ALALAL added as shown.…”

“…Transmembrane domains generally consist of 20-25 non-polar amino acids (Lemmon et al, 1997). By containing between 14 and 19 aa (Cocquerel et al, 2000;Zhang et al, 2003a), the transmembrane segments of prM and E are rather short. In addition, although a lysine residue is observed at the N terminus of the transmembrane segment of E of some flaviviruses, the transmembrane segments of prM and E do not contain any charge or hydrophilic residue in their middle (Cocquerel et al, 2000).…”

“…By containing between 14 and 19 aa (Cocquerel et al, 2000;Zhang et al, 2003a), the transmembrane segments of prM and E are rather short. In addition, although a lysine residue is observed at the N terminus of the transmembrane segment of E of some flaviviruses, the transmembrane segments of prM and E do not contain any charge or hydrophilic residue in their middle (Cocquerel et al, 2000). Furthermore, they do not contain any positive export signal, such as the well-characterized diacidic motif (DE)X(DE) (Nishimura & Balch, 1997).…”

“…A sequence alignment of the transmembrane regions of YFV, dengue virus 1 (DEN1), West Nile virus (WNV) and Japanese encephalitis virus (JEV) is shown. The putative minimal transmembrane sequences (Cocquerel et al, 2000) are indicated by # . (b) Schematic diagrams of CD4 and chimeras containing the CD4 ectodomain fused to wild-type or mutated TM1 of E containing or not the cytosolic tail of vesicular stomatitis virus glycoprotein (VSV-G), mutated (CD4-TM1E-G mut ) or not (CD4-TM1E-G) in the DIE motif.…”