Biology subjects

Wachsmuth-Melm, M.

Publications and source records attributed to Wachsmuth-Melm, M..

4 recordsLinked to original sources

bioRxiv2023

Nucleocapsid condensation drives Ebola viral factory maturation and dispersion

Replication and genome encapsidation of many negative-sense RNA viruses take place in virus-induced membrane-less organelles termed viral factories (VFs). While liquid properties of VFs are believed to control the transition from genome replication to encapsidation, the nucleocapsid assembly, VF maturation and interactions with the cellular environment remain elusive. Here we apply in situ cryo-correlative light and electron tomography to follow nucleocapsid assembly and changes in VF morphology and their liquid properties during Ebola virus infection. We show that Ebola viral nucleocapsids transition from loosely packed helical assemblies in early VFs to condensed cylinders that arrange into highly organized parallel bundles later in infection. Early VFs associate with intermediate filaments and are devoid of other host material, but become progressively accessible to cellular components. Our data suggest that this process is coupled to VF solidification and dispersion, and that changes in liquid properties of VFs promote nucleocapsid transport to budding sites. Highlights- Cryo-ET reveals the molecular architecture of Ebola virus replication compartments - Loosely coiled nucleocapsids transition to condensed cylinders forming bundles - Nucleocapsid condensation drives dispersion of viral factories promoting viral egress - Intermediate filaments associate with and are critical for virus factory formation

microbiology↗

bioRxiv2022

SARS-CoV-2 nsp3-4 suffice to form a pore shaping replication organelles

Coronavirus replication is associated with the remodeling of cellular membranes resulting in the formation of double-membrane vesicles (DMVs). Recently, a pore spanning DMV was identified as a putative portal for viral RNA transcription and replication products providing a novel target for antiviral intervention. However, the exact components and the structure of the SARS-CoV-2 pore remain to be determined. Here, we investigate the structure of DMV pores by in situ cryo-electron tomography combined with subtomogram averaging. We reveal non-structural proteins (nsp) 3 and 4 as minimal components forming a DMV spanning pore and show that nsp3 Ubl1-Ubl2 domains are critical for inducing membrane curvature and DMV formation. Altogether, SARS-CoV-2 nsp3-4 has a dual role by driving the biogenesis of replication organelles and forming DMV-spanning replicopores. One-Sentence SummaryBiogenesis of SARS-CoV-2 replication organelles is driven by nsp3-4 constituting the double-membrane vesicle spanning pore.

microbiology↗

bioRxiv2022

IFITM3 blocks viral entry by sorting lipids and stabilizing hemifusion

Interferon-induced transmembrane protein 3 (IFITM3) inhibits the entry of numerous viruses through undefined molecular mechanisms. IFITM3 localizes in the endosomal-lysosomal system and specifically impacts virus fusion with target cell membranes. We found that IFITM3 induces local lipid sorting, resulting in an increased concentration of lipids disfavoring viral fusion at the hemifusion site. This increases the energy barrier for fusion pore formation and the hemifusion dwell time, promoting viral degradation in lysosomes. In situ cryo-electron tomography captured IFITM3-mediated arrest of influenza A virus membrane fusion. Observation of hemifusion diaphragms between viral particles and late endosomal membranes confirmed hemifusion stabilization as a molecular mechanism of IFITM3. The presence of the influenza fusion protein hemagglutinin in post-fusion conformation close to hemifusion sites further indicated that IFITM3 does not interfere with the viral fusion machinery. Collectively, these findings show that IFITM3 induces lipid sorting to stabilize hemifusion and prevent virus entry into target cells.

molecular biology↗

bioRxiv2020

SARS-CoV-2 structure and replication characterized by in situ cryo-electron tomography

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of the COVID19 pandemic, is a highly pathogenic {beta}-coronavirus. As other coronaviruses, SARS-CoV-2 is enveloped, replicates in the cytoplasm and assembles at intracellular membranes. Here, we structurally characterize the viral replication compartment and report critical insights into the budding mechanism of the virus, and the structure of extracellular virions close to their native state by in situ cryo-electron tomography and subtomogram averaging. We directly visualized RNA filaments inside the double membrane vesicles, compartments associated with viral replication. The RNA filaments show a diameter consistent with double-stranded RNA and frequent branching likely representing RNA secondary structures. We found that assembled S trimers in lumenal cisternae do not alone induce membrane bending but laterally reorganize on the envelope during virion assembly. The viral ribonucleoprotein complexes (vRNPs) are accumulated at the curved membrane characteristic for budding sites suggesting that vRNP recruitment is enhanced by membrane curvature. Subtomogram averaging shows that vRNPs are distinct cylindrical assemblies. We propose that the genome is packaged around multiple separate vRNP complexes, thereby allowing incorporation of the unusually large coronavirus genome into the virion while maintaining high steric flexibility between the vRNPs.

microbiology↗