8AXX

Expanded Coxsackievirus A9 after treatment with endosomal ionic buffer

Summary for 8AXX

• Entry DOI: 10.2210/pdb8axx/pdb
• EMDB information: 15634 15692 15706
• Descriptor: Capsid protein VP1, Capsid protein VP2, Capsid protein VP3 (3 entities in total)
• Functional Keywords: icosahedral symmetry, expanded virion, picornavirus, a-particle, virus
• Biological source: Human coxsackievirus A9 (strain Griggs); More
• Total number of polymer chains: 3
• Total formula weight: 89089.61

Authors

Domanska, A.,Plavec, Z.,Ruokolainen, V.,Loflund, B.,Marjomaki, V.S.,Butcher, S.J. (deposition date: 2022-09-01, release date: 2022-10-19, Last modification date: 2024-07-24)

Primary citation

Domanska, A.,Plavec, Z.,Ruokolainen, V.,Loflund, B.,Marjomaki, V.,Butcher, S.J.
Structural Studies Reveal that Endosomal Cations Promote Formation of Infectious Coxsackievirus A9 A-Particles, Facilitating RNA and VP4 Release.
J.Virol., 96:e0136722-e0136722, 2022

PubMed Abstract: Coxsackievirus A9 (CVA9), an enterovirus, is a common cause of pediatric 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 showed that CVA9 treatment with albumin or endosomal ions generated a heterogeneous population of virions, which could be physically separated by asymmetric flow field flow fractionation and computationally by cryo-electron microscopy (cryo-EM) and image processing. We report cryo-EM structures of CVA9 A-particles obtained by albumin or endosomal ion treatment and a control nonexpanded virion to 3.5, 3.3, and 2.9 Å resolution, respectively. Whereas albumin promoted stable expanded virions, the endosomal ionic concentrations induced unstable CVA9 virions which easily disintegrated, losing their genome. Loss of most of the VP4 molecules and exposure of negatively charged amino acid residues in the capsid's interior after expansion created a repulsive viral RNA-capsid interface, aiding genome release. Coxsackievirus 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 externalized, 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.

PubMed: 36448797
DOI: 10.1128/jvi.01367-22

Experimental method

ELECTRON MICROSCOPY (3.3 Å)