posted on 2020-03-05, 21:45authored byKevin
M. Bond, Nicholas A. Lyktey, Irina B. Tsvetkova, Bogdan Dragnea, Martin F. Jarrold
Capsid disassembly and genome release are critical steps in the
lifecycle of a virus. However, their mechanisms are poorly understood,
both in vivo and in vitro. Here, we have identified two in vitro disassembly
pathways of the brome mosaic virus (BMV) by charge detection mass
spectrometry and transmission electron microscopy. When subjected
to a pH jump to a basic environment at low ionic strength, protein–RNA
interactions are disrupted. Under these conditions, BMV appears to
disassemble mainly through a global cleavage event into two main fragments:
a near complete capsid that has released the RNA and the released
RNA complexed to a small number of the capsid proteins. Upon slow
buffer exchange to remove divalent cations at neutral pH, capsid protein
interactions are disrupted. The BMV virions swell but there is no
measurable loss of the RNA. Some of the virions break into small fragments,
leading to an increase in the abundance of species with masses less
than 1 MDa. The peak attributed to the BMV virion shifts to a higher
mass with time. The mass increase is attributed to additional capsid
proteins associating with the disrupted capsid protein–RNA
complex, where the RNA is presumably partially exposed. It is likely
that this pathway is more closely related to how the capsid disassembles
in vivo, as it offers the advantage of protecting the RNA with the
capsid protein until translation begins.