Ruokolainen, V. | Search bioRxiv

bioRxiv2023

Progression of herpesvirus infection remodels mitochondrial organization and metabolism

Viruses target mitochondria to promote their replication, and infection-induced stress during the progression of infection leads to the regulation of antiviral defenses and mitochondrial metabolism which are opposed by counteracting viral factors. The precise structural and functional changes that underlie how mitochondria react to the infection remain largely unclear. Here we show extensive transcriptional remodeling of protein-encoding host genes involved in the respiratory chain, apoptosis, and structural organization of mitochondria as herpes simplex virus type 1 lytic infection proceeds from early to late stages of infection. High-resolution microscopy and interaction analyses unveiled infection-induced emergence of rough, thin, and elongated mitochondria relocalized at the perinuclear area, a significant increase in the number and clustering of ER-mitochondria contact sites, and thickening and shortening of mitochondrial cristae. Finally, metabolic analyses demonstrated that reactivation of ATP production is accompanied by increased mitochondrial Ca2+ content and proton leakage as the infection proceeds. Overall, the significant structural and functional changes in the mitochondria triggered by the viral invasion are tightly connected to the progression of the virus infection.

microbiology↗

bioRxiv2022

Structural studies reveal that endosomal cations promote formation of infectious CVA9 A particles, facilitating RNA and VP4 release.

Coxsackievirus A9, an enterovirus, is a common cause of paediatric aseptic meningitis and neonatal sepsis. During cell entry, enterovirus capsids undergo conformational changes leading to expansion, formation of large pores, externalization of VP1 N-termini and loss of the lipid factor from VP1. Factors such as receptor binding, heat, and acidic pH can trigger capsid expansion in some enteroviruses. Here we show that fatty-acid free bovine serum albumin or neutral endosomal ionic conditions can independently prime CVA9 for expansion and genome release. Our results show that CVA9 treatment with albumin or endosomal ions generates a heterogeneous population of virions, which could be physically separated by asymmetric flow field flow fractionation and computationally by cryo-EM and image processing. We report cryo-EM structures of CVA9 A-particles obtained by albumin or endosomal ion treatment and a control non-expanded virion to 3.5, 3.3 and 2.9 [A] resolutions, respectively. Where albumin promotes stabile expanded virions, the endosomal ionic concentrations induce unstable CVA9 virions which easily disintegrate losing their genome. Loss of most of the VP4 molecules and exposure of negatively-charged amino acid residues in the capsids interior after expansion, create a repulsive viral RNA-capsid interface, aiding genome release. ImportanceCoxsackievirus A9 (CVA9) is a common cause of meningitis and neonatal sepsis. The triggers and mode of action of RNA release into the cell unusually do not require receptor interaction. Rather, a slow process in the endosome, independent of low pH is required. Here, we show by biophysical separation, cryogenic electron microscopy and image reconstruction that albumin and buffers mimicking the endosomal ion composition can separately and together expand and prime CVA9 for uncoating. Furthermore, we show in these expanded particles that VP4 is present at only ~10% of the occupancy found in the virion, VP1 is externalised and the genome is repelled by the negatively-charged, repulsive inner surface of the capsid that occurs due to the expansion. Thus, we can now link observations from cell biology of infection with the physical processes that occur in the capsid to promote genome uncoating.

microbiology↗