Zika virus M protein as a viroporin drug target

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.