The Extracellular Domain of La Crosse Virus G1 Forms Oligomers and Undergoes PH-dependent Conformational Changes

The La Crosse virus G1 glycoprotein plays a critical role in virus binding to susceptible cells and in the subsequent fusion of viral and cellular membranes. A soluble form of the G1 glycoprotein (sG1) prepared in a recombinant baculovirus system mimics the cell-binding pattern of La Crosse virus and inhibits La Crosse virus infection (A. Pekosz et al., Virology 214, 339-348, 1995), presumably by competing for a cellular receptor, a finding that implies that sG1 can perform some functions absent G2, the smaller of the two bunyavirus glycoproteins. We have performed experiments to determine whether sG1 is present as an oligomer and whether it undergoes the conformational changes associated with fusion (F. Gonzalez-Scarano, Virology 140, 209-216, 1985). Our results indicate that both sG1 and native G1 undergo similar changes in conformation after exposure to an acidic environment, as detected by reactivity with monoclonal antibodies. Furthermore, using chemical cross-linking, both proteins were detected as oligomers (most likely dimers). Sucrose density gradient analysis of sG1 verified that it was present in monomeric and oligomeric forms. These results demonstrate that the isolated G1 glycoprotein can undergo a pH-dependent change in conformation in the absence of its transmembrane and cytoplasmic tall domains and that the extracellular portion of the glycoprotein can oligomerize.