Biomedical Engineering Reference
In-Depth Information
hybrid. virus-mineral. nanoparticles.. Douglas. and. Young. pioneered. the. use. of. CCMV.
for. biotemplating. purposes. in. 1998. (Douglas. and. Young. 1998).. They. demonstrated.
mineralization. of. tungsten. by. incubating. the. empty. virion. with. tungstate. ions. (WO 4 2− ).
at. pH.>.6.5,. where. the. capsid. is. in. an. expanded. state.. Subsequently,. lowering. the. pH.
closed.the.pores.and.facilitated.formation.of.paratungstate.(H 2 W 12 O 42 10− ).inside.the.capsid.
that. precipitated. upon. adding. ammonia.. X-ray. diffraction. and. TEM. images. showing.
lattice. fringes. consistent. with. the. ammonium. salt. (NH 4 ) 10 H 2 W 12 O 42 .×.4H 2 O. conirmed.
mineralization.. In. a. similar. fashion,. they. also. demonstrated. entrapment. of. vanadate.
and. molybdate. (Douglas. and. Young. 1998,. 1999).. More. recently,. β-TiO 2 . with. photoactive.
properties.has.been.synthesized.through.this.bioinspired.approach.(Jolley.et.al..2011,.Klem.
et.al..2008)..Douglas.et.al..have.also.engineered.a.CCMV.coat.protein.recombinant,.where.
they.replaced.nine.basic.amino.acids.in.the.N-terminus.with.glutamic.acid.to.mimic.the.
function.of.the.ferritin.light.chain.(Douglas.et.al..2002)..This.modiication.causes.a.drastic.
change.in.charge.(net.change.of.3240.units).but.does.not.interfere.with.the.self-assembly.
process.and.enables.site-speciic.oxidative.hydrolysis.of.Fe(II).to.iron.oxide.nanoparticles.
inside. the. capsid.. Slocik. et. al.. used. a. comparable. approach. where. they. replaced. the.
N-terminus. with. short. metal-binding. peptides. (His/Tyr. rich). in. an. attempt. to. template.
gold,. using. AuCl 4 . (Slocik. et. al.. 2005).. Although. gold. nanoparticles. could. form. inside.
the.capsid,.they.noted.that.a.cluster.of.exposed.tyrosines.from.the.C-terminus.provides.
electrons.for.reducing.Au 3+ .to.Au 0 ,.which.aggregate.on.the.outside.surface..Leveraging.the.
tyrosine.clusters'.reductive.properties.and.using.AuCIP(CH 3 ) 3 .as.a.precursor,.the.capsid.
exterior.could.be.uniformly.decorated.with.small.nanoparticles.
7.2.4  encapsulation
The.ability.of.the.CCMV.coat.protein.to.assemble.to.virus-like.particles.(VLPs).in.vitro,.
as. long. as. the. N-terminal. charges. are. neutralized,. makes. it. an. interesting. choice. for.
encapsulation.of.exogenous.material.and.turns.it.into.a.“cargo.container.”.Since.RNA.is.
negatively.charged,.a.logical.approach.would.be.to.encapsulate.anionic.polymers,.which.
have.similar.charge.properties..Indeed,.mixing.negatively.charged.sodium.polyanethole.
sulfonate.(PAS).and.CCMV.coat.protein.at.pH.7.5,.followed.by.dialysis.to.pH.4.5,.Douglas.
demonstrated. that. it. was. possible. to. assemble. “native. like”. T.=.3. symmetry. particles.
containing. PAS. (Douglas. and. Young. 1998).. In. a. similar. manner,. polystyrene. sulfonate.
(PSS,.∼10.kDa).has.been.packaged.into.VLPs.(Sikkema.et.al..2007)..The.sizes.of.the.VLPs.
were.dependent.on.the.PSS:protein.ratio,.although.VLPs.with.a.smaller.diameter.(∼16.nm).
and.T1.symmetry.were.assembled.most.eficiently..Increasing.the.PSS.molecular.weight.
favors.the.formation.of.larger.VLPs.in.“quantized”.steps,.irst.to.22.nm.(T.=.2).and.then.
to.27.nm.(T.=.3).at.2.MDa.(Comellas-Aragones.et.al..2011,.Hu.et.al..2008)..It.is.likely.that.
the.polymer.gradually.ills.up.the.empty.core,.at.which.point.the.next.stable.symmetry.
coniguration. will. form.. Other. negative. polyanions. have. been. packaged. into. VLPs. as.
well,. such. as. redox-active. polyferrocenylsilane. (PFS). and. luorescent. poly-2-methoxy-
5-propyloxy. sulfonate. phenylene. vinylene. (MPS-PPV). (Minten. et. al.. 2009b,. Ng. et. al..
2011).. Interestingly,. the. MPS-PVP. forms. rod-like. structures. at. lower. ionic. strengths,.
which.could.be.an.effect.of.the.relatively.stiff.polymer.chain..When.dsDNA.are.used.as.
assembly. templates,. ∼16.nm. diameter. rods. form. rather. than. spherical. particles,. where.
the. rod. length. correlates. to. the. size. of. the. DNA. (Mukherjee. et. al.. 2006).. Compared. to.
ssRNA.and.polymers,.dsDNA.strands.are.less.lexible.and.this.could.be.one.reason.for.
the. preferential. assembly. into. rods.. The. stiffness. effect. on. VLP. size/shape. was. also.
noted. when. single-stranded. oligothymine. templates. were. used. to. package. various.
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