Role of disulfide bond formation in the folding and assembly of the envelope glycoproteins of a pestivirus

Abstract

Bovine viral diarrhea virus (BVDV) is a pestivirus member of the Flaviviridae family, closely related to, and used as a surrogate model for the hepatitis C virus. Its envelope contains the E1 and E2 glycoproteins, disulfide linked into homo- and heterodimers. In this study, we investigate the role of disulfide bond formation in the folding, assembly, and stability of BVDV glycoproteins. We provide molecular evidence that intact disulfide bonds are critical for the acquirement of a stable conformation of E2 monomers. Forcing the E2 glycoproteins to adopt a reduced conformation either co- or post-translationally before assembly into dimers, determines their misfolding and degradation by proteasome. In contrast, dimerization of E2 glycoproteins results in a conformation resistant to reducing agents and degradation. Furthermore, inhibition of the ER-alpha-mannosidase activity leads to impairment of misfolded E2 degradation, demonstrating the involvement of this enzyme in targeting viral proteins towards proteasomal degradation.

Bovine Viral Diarrhoea Virus is Internalized by Clathrin‐dependent Receptor‐mediated Endocytosis

“…This is in concert with our former findings that MAb BVD/C42 does not react with the Erns protein in Western blot under reducing conditions. In contrast, it could be demonstrated previously that E2 dimers are resistant to reducing agents and degradation and possess a pH stability (Branza-Nichita et al, 2002) which supports our findings. Biochemically, BVDV infection of susceptible cells was inhibited by two drugs that interfere with the clathrindependent pathway but not by drugs that inhibit the caveolae-dependent pathway.…”

Antiviral effect of α-glucosidase inhibitors on viral morphogenesis and binding properties of hepatitis C virus-like particles

“…It is not clear why potentially misfolded HCV glycoproteins accumulate in the ER of infected insect cells. This result differs from those obtained with BVDV, where it was shown that misfolded glycoproteins were degraded by the proteasome and did not accumulate in the ER of BVDV-infected Madin-Darby bovine kidney cells (Branza-Nichita et al, 2002). This accelerated degradation of misfolded BVDV glycoproteins caused a reduction in the amount of prebudding complexes, which was proposed tentatively as one possible explanation for the inhibition of viral secretion.…”

The Molecular Biology of Pestiviruses

“…Moreover, a disulfide bridge is established with E2 leading to covalently bound heterodimers. The formation of the E1-E2 heterodimer is slow (R€ umenapf et al, 1993) which might be due to the slow folding of E1 (Branza-Nichita, Durantel, Carrouee-Durantel, Dwek, & Zitzmann, 2001;Branza-Nichita, Lazar, Durantel, Dwek, & Zitzmann, 2002). E1 interacts transiently with calnexin (>30 min), and the formation of E1-E2 heterodimers starts after correct folding and release of E1 from calnexin.…”