Structural basis of local ER membrane curvature inversion during flavivirus replication

Flaviviruses are positive-sense RNA viruses whose intracellular replication is marked by endoplasmic reticulum (ER) membraneremodelling. The genome replication step is one of the least understood processes in the viral life cycle. The ER membrane normallyhas a positive curvature which is maintained by cellular reticulon proteins.

Upon flavivirus infection, the ER membrane curvature islocally altered by viral proteins forming inverted buds, called replication complexes (RCs).

RCs are the site of viral genome replication.The viral genome is translated as a single polyprotein comprising both capsid and non-capsid (“non-structural”, NS) proteins. NSproteins replicate the viral genome.

The function is well established for the helicase NS3 and the polymerase NS5, but remainsunknown for the transmembrane NS proteins.I hypothesise that flavivirus-induced ER membrane invaginations, which shelter the viral RNA replication, are generated bytransmembrane NS proteins acting as “anti-reticulons”.

I propose that these proteins form hetero-oligomeric complexes that localiseto specific regions of the membrane bud and act by inverting the membrane curvature of the ER. To test this hypothesis, I will workwith Langat virus (a BSL2 model system for Tick-borne encephalitis virus).

I will integrate methods of virology, structural biology ofisolated protein complexes, and in situ structural studies of infected cells using cryo-electron tomography (cryo-ET).

This study willprovide insights into the interplay of flaviviral protein in ER shaping within the context of viral infection and disease progression.