Zika virus (ZIKV) an arbovirus that became widely known in 2015 due to the
epidemic in Brazil, spreading across South and North America. Whilst previous
Old World ZIKV outbreaks comprised largely mild, or even asymptomatic
infections, the New World epidemic became notorious for its association with
foetal microcephaly following maternal infection, and an increased incidence of
various neurological symptoms, including Guillain-Barré syndrome.
Mature, infectious ZIKV particles comprise three structural proteins, Capsid (C),
small Membrane (M) and the envelope (E) glycoprotein; the latter is responsible
for receptor binding and mediates membrane fusion upon encountering low pH
within the acidifying endosome. However, the function of M within this context is
unknown.
Based upon its structural similarity to “viroporins”, a class of virus-coded ion
channels mediating virus entry and uncoating, we investigated whether M could
form alternative oligomeric forms to the dimeric structure seen within mature
virions, and in so doing exhibit channel activity. Gratifyingly, M peptides adopted
higher order structures within membrane-mimetic environments and displayed
channel activity in vitro, sensitive to the prototypic viroporin inhibitor,
Rimantadine. Accordingly, ZIKV entry was blocked in a dose-dependent fashion
by the drug, which also prevented virus spread in mouse models of ZIKV
infection. Molecular dynamics simulations supported that M protein is able to
oligomerise into a hexameric viroporin channel, opening of which was within
acidified environments via protonation of a conserved histidine residue.
Rimantadine was predicted in silico to interact at a lumenal binding site, against
which we derived improved inhibitors from a library of generic, FDA-approved
and other bio-active small molecules, providing a basis for novel M protein
targeted drug discovery. Significantly, due to its role during virus entry, M targeted drugs might either prevent or reduce the severity of ZIKV infections,
including those crossing the placenta, and may also show activity against
closely related M proteins from other Flaviviruses.
