Low pH induces swiveling of the glycoprotein heterodimers in the Semliki forest virus spike complex

Abstract

Time-resolved cryoelectron microscopy reveals the first step in the conformational changes that enable membrane fusion in Semliki Forest virus. The neutral pH structure reveals a central cavity within the spike complex, plate-like extensions forming a layer above the membrane, and the paths of the paired transmembrane domains connecting the trimeric spikes and pentamer-hexamer clustered capsid subunits. Low pH treatment results in centrifugal movement of E2, the receptor-binding subunit, centripetal movement of E1 to narrow the central cavity initiating the formation of an E1 trimer, and the extension of the E1 fusion sequence toward the target membrane.

Molecular mechanism of pathogenesis of dengue virus: Entry and fusion with target cell

“…The three E monomers per icosahedral asymmetric unit do not have quasi-equivalent symmetric environment. In addition, structures of immature dengue and yellow fever virus particles were determined to 16A and 25A resolution, respectively (Fuller et a/., 1995). The closely similar structures show 60 icosahedrallyorganized, trimeric spikes on the particle surface.…”

A Model-Based Approach for Determining Orientations of Biological Macromolecules Imaged by Cryoelectron Microscopy

“…As a test, we reexamined the same 1.2-m image with Common Lines and were only able to identify the correct orientation view for 1 of the 21 CaMV particle images that went into the original 3D reconstruction. Similarly, the success rate of Common Lines in finding orientations of low pH-treated Semliki Forest viruses was less than 10% (Fuller et al, 1995). We have now used the PFT method to successfully examine a large number of viruses from micrographs recorded at ഛ1.5 m defocus (Cheng et al, 1994a(Cheng et al, ,b, 1995Hagensee et al, 1994;Wikoff et al, 1994;Ilag et al, 1995;Zhao et al, 1995).…”

“…The PFT method has been used by us as well as others to determine the structures of several icosahedral viruses (e.g., Dokland and Murialdo, 1993;Cheng et al, 1994aCheng et al, ,b, 1995Hagensee et al, 1994;Kenney et al, 1994;Venién-Bryan and Fuller, 1994;Wikoff et al, 1994;Fuller et al, 1995;Ilag et al, 1995;Zhao et al, 1995). The method could also be adapted for the analysis of asymmetric macromolecules or those with lower symmetry than an icosahedron.…”

“…tively stained specimens, but can lead to inconsistent results when applied to low-contrast, noisy images of unstained, vitrified specimens (e.g., Fuller et al, 1995). A statistical method that helps overcome some limitations of this method was developed by Fuller (1987), whose ''Modified Common Lines'' method is described elsewhere in this issue (Fuller et al, 1996).…”

Do lipid rafts mediate virus assembly and pseudotyping?

“…Budding from the plasma membrane occurs in an environment of~30 000 plasma membrane proteins per square micron (Griffiths et al, 1984;Quinn et al, 1984;. The surface density of viral proteins in a budded virion is easiest to calculate for an icosahedral enveloped virus such as Semliki Forest virus (SFV), which has~25 000 spike complexes per square micron (Fuller et al, 1995;Mancini et al, 2000;. Hence, virus budding does not lead to a significant change in the concentration of surface proteins within the budding particle but rather selection of the proteins from the mixed population at the cell surface.…”