Highly Basic Clusters in the Herpes Simplex Virus 1 Nuclear Egress Complex Drive Membrane Budding by Inducing Lipid...

Area of Science:

• Virology
• Structural Biology
• Biophysics

Background:

• Herpesviruses replicate by exporting capsids from the nucleus via membrane budding.
• The viral nuclear egress complex (NEC) mediates this by forming a scaffold that deforms the inner nuclear membrane.
• The precise biophysical mechanism of NEC-mediated membrane deformation remains unclear.

Purpose of the Study:

• To elucidate the biophysical mechanisms by which the herpes simplex virus 1 NEC deforms the nuclear membrane.
• To investigate the role of electrostatic interactions and phosphorylation in NEC function.
• To explore potential therapeutic strategies targeting NEC-mediated nuclear egress.

Main Methods:

• Investigated membrane-proximal regions (MPRs) of the NEC for their interaction with lipid bilayers.
• Utilized biophysical techniques to assess membrane deformation, lipid ordering, and curvature induction.
• Employed phosphomimicking mutations to study the effect of phosphorylation on NEC activity in vitro and in vivo.

Main Results:

• Highly basic MPRs of the NEC insert into lipid headgroups, altering lipid order and promoting negative Gaussian curvature.
• Electrostatic interactions between MPRs and membranes are critical for membrane deformation.
• Phosphorylation of an MPR by a viral kinase inhibits NEC-mediated budding by disrupting membrane interactions, acting as an 'off switch'.

Conclusions:

• The NEC utilizes both lipid ordering and protein scaffolding to generate negative membrane curvature for nuclear egress.
• Phosphorylation serves as a regulatory mechanism to control NEC activity, preventing capsid-less budding.
• Targeting NEC-membrane interactions presents a promising therapeutic avenue for controlling herpesvirus infections.