The COVID-19 pandemic has demonstrated the world’s vulnerability to biological catastrophe and elicited unprecedented scientific efforts. Some of this work and its derivatives, however, present dual-use risks (i.e., potential harm from misapplication of beneficial research) that have largely gone unaddressed.
Ferritin-based, self-assembling protein nanoparticle
vaccines are
being developed against a range of viral pathogens, including SARS-CoV-2,
influenza, HIV-1, and Epstein-Barr virus. However, purification of
these nanoparticles is often laborious and requires customization
for each potential nanoparticle vaccine. We propose that the simple
insertion of a polyhistidine tag into exposed flexible loops on the
ferritin surface (His-Fer) can mitigate the need for complex purifications
and enable facile metal-chelate-based purification, thereby allowing
for optimization of early stage vaccine candidates. Using sequence
homology and computational modeling, we identify four sites that can
accommodate insertion of a polyhistidine tag and demonstrate purification
of both hemagglutinin-modified and SARS-CoV-2 spike-modified ferritins,
highlighting the generality of the approach. A site at the 4-fold
axis of symmetry enables optimal purification of both protein nanoparticles.
We demonstrate improved purification through modulating the polyhistidine
length and optimizing both the metal cation and the resin type. Finally,
we show that purified His-Fer proteins remain multimeric and elicit
robust immune responses similar to those of their wild-type counterparts.
Collectively, this work provides a simplified purification scheme
for ferritin-based vaccines.
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