Frozen in Time

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Science  15 Aug 2008:
Vol. 321, Issue 5891, pp. 892
DOI: 10.1126/science.321.5891.892d

Insights into how an enveloped virus fuses with a cellular membrane have come primarily from high-resolution structures of individual virus proteins and from real-time, low-resolution fluorescence microscopy trajectories of virus particles during entry. Maurer et al. have used cryoelectron tomography to reconstruct three-dimensional images of herpes simplex virus type 1 (HSV-1) particles frozen in the process of entering kidney cells and synaptic nerve endings. HSV-1 particles consist of a glycoprotein-rich outer membrane surrounding an amorphous protein layer (the tegument) and an icosahedral capsid housing the DNA genome. Capsids (cyan in the figure) released into the cytoplasm left their clustered envelope glycoproteins (yellow) and tegument proteins (orange) at the site of entry and had entered the actin network (red) apparently without local actin depolymerization. Among the virus particles found docked at target cells were two whose envelopes had already been pulled into contact with the target membrane; one of these contained an open fusion pore of 25-nm diameter, indicating that the pore had already started expanding. In both cases, neighboring the region of membrane contact were hints of V-shaped densities connecting the membranes that could represent viral fusion proteins. — NM*

Proc. Natl. Acad. Sci. U.S.A. 105, 10559 (2008).

  • *Nilah Monnier is a summer intern in Science's editorial department.

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