Formation of heterotrimers between the membrane-integrated and the soluble glycoproteins of vesicular stomatitis virus leads to their intracellular cotransport

Abstract

BHK cells infected with vesicular stomatitis virus serotype Indiana generate intracellularly two different types of glycoproteins: the authentic membrane-integrated G protein ofvirions and a smaller soluble Gs protein lacking the transmembrane and cytoplasmic domains which is secreted into the growth medium. A Gsl protein species which is formed during or shortly after translation in the endoplasmic reticulum lumen is modified in the same way as the Gl protein by endoglycosidase H-sensitive oligosaccharides of the high-mannose type. Both Gl and Gsl are almost simultaneously transported, trimmed, and processed into G2 and Gs2 species which possess carbohydrate side chains of the complex type, making both glycoproteins resistant to endoglycosidase H cleavage. Secretion of Gs2 protein into the growth medium and arrival of G2 protein on the cell surface occur concomitantly. Membrane-integrated G protein and the soluble Gs protein molecules oligomerize intracellularly into heterotrimers which can be immunoprecipitated after chemical cross-linking. Gs protein seems to contain sufficient structural information for the formation of heterotrimers which are efficiently transported to the cell surface. Heterotrimer formation between G and Gs proteins explains the rapid secretion of Gs molecules.

A Subset of Porcine Reproductive and Respiratory Syndrome Virus GP 3 Glycoprotein Is Released into the Culture Medium of Cells as a Non-Virion-Associated and Membrane-Free (Soluble) Form

“…For instance, the ORF2 product of EAV (G s protein) is retained in the ER in its monomeric state, whereas dimers become Endo H resistant and are selectively incorporated into virus particles (13). Heterotrimer formation between the authentic membrane-integrated G protein of vesicular stomatitis virus and the smaller soluble G s fraction is required for secretion of the latter into the growth medium (51). By using monomer-and oligomer-specific antibodies to influenza virus hemagglutinin, it was shown that monomers are restricted to the ER, whereas assembled molecules are able to reach distal points in the transport pathway (9).…”

Release of polymannose oligosaccharides from vesicular stomatitis virus G protein during endoplasmic reticulum-associated degradation

“…After visualization by fluorography the G protein (Mr = 70 kDa) was quantitated by densitometry and the average of duplicate experiments is shown by the bar graphs. The minor faster moving component is believed to represent the soluble (G S ) protein (Schmidt et al, 1992).…”

Structure of the rabies virus glycoprotein trimer bound to a pre-fusion specific neutralizing antibody

“…The role of shed RABV-G during infection is unknown, but it may serve as a decoy for the immune system, as has been observed for other viruses (26)(27)(28). Furthermore, shed VSV-G has been reported to bind to full-length glycoprotein for uptake into cells (23) and injection of soluble RABV-G ectodomains into the brains of mice increases locomotion (29), a rabies symptom believed to facilitate transmission to new hosts.…”

“…Challenges in developing longer lasting rabies vaccines include the lack of the quality and durability of the resulting neutralizing antibody response, and the lack of efficacy of most antibodies against other emerging and circulating lyssaviruses [22,23]. Monoclonal antibody RVA122 is the type of antibody desired from rabies immunization.…”

“…In rhabdoviruses, the full-length glycoprotein can be either membrane-anchored or proteolytically cleaved near the transmembrane domain, releasing a shed ectodomain (23)(24)(25).…”