Poster No. 50
Title:
Syncytial Phenotype of HSV-1 gB Is Associated with Diminished Membrane Interactions
Authors:
Tirumala Chowdary and Ekaterina Heldwein
Presented by:
Tirumala Chowdary
Department:
Department of Molecular Biology and Microbiology, Tufts University School of Medicine
Abstract:
In herpes viruses, glycoprotein B (gB) is a key component of the viral entry machinery, being required for
membrane fusion. The cytoplasmic domain of gB is thought to negatively regulate membrane fusion by a yet
unidentified mechanism. C-terminal truncations of the cytoplasmic domain of gB from Herpes Simplex virus
type 1 (HSV-1) lead to either a hyperfusion or fusion-null phenotype. To provide a biochemical rationale for
these phenotypes, we used circular dichroism spectroscopy and size-exclusion chromatography to characterize
the secondary structure and oligomeric state of full-length and truncated cytoplasmic domains of HSV-1 gB
both in solution and with lipid membranes. In solution, the full-length cytoplasmic domain is a trimer containing
helical secondary structure. Moreover, the cytoplasmic domain stably associates with anionic lipid membranes
and this interaction leads to increased helicity in the protein. We did not find any notable differences in
secondary structure or oligomeric state of the full-length or truncated cytoplasmic domains in aqueous solution.
However, the truncated and the full-length cytoplasmic domains differed significantly in terms of membrane
interactions. The mutant associated with the hyperfusion phenotype, gB (801 – 868), showed a smaller increase
in helical structure and a diminished association with lipid membranes. The mutant associated with the fusionnull phenotype, gB (801 – 851), showed no increase in helical structure and only minimal association with lipid
membranes. Based on our results, we propose that residues 869–882 form a helix in the presence of anionic lipid
membranes, which allows the cytoplasmic domain of gB to stably associate with membranes. We hypothesize
that this event is an important part of the mechanism by which the cytoplasmic domain negatively regulates
membrane fusion.
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