Biomedical Engineering Reference
In-Depth Information
MS2
Ø= 28 nm
RCNMV
Ø= 36 nm
CCMV
Ø= 29 nm
CPMV
Ø= 28 nm
TMV
L= 300 nm
W= 18 nm
M13
L= 900 nm
W= 7 nm
Figure 7.2
(See companion CD for color igure.)
. Surface.representations. showing.the. capsids.of. six.virus.systems. that.
have.frequently.been.used.in.nanobiotechnology.
The.RNA.in.CCMV.adopts.an.ordered.structure.at.each.quasi-threefold.axis.and.lines.the.
capsid.interior.to.leave.a.hollow.core.about.18.nm.in.diameter.(Fox.et.al..1998,.Zhao.et.al..
1995).. While. the. interior. has. a. strong. positive. electrostatic. potential,. the. exterior. capsid.
surface.displays.a.slightly.electronegative.potential.(Konecny.et.al..2006).
CCMV.exhibits.pH.and.ionic-strength-dependent.swelling..The.virus.is.stable.between.
pH.3.0-6.0.where.it.exists.in.its.native.state;.whereas.at.pH.7.0.and.lower.ionic.strengths.
(<.0.1.M).the.capsid.swells.about.10%.(Bancroft.et.al..1967b,.Lavelle.et.al..2007)..The.main.
structural. change. under. these. conditions. is. an. expansion. at. the. quasi-threefold. axis. to.
open.up.∼2.nm.diameter.pores.(Douglas.and.Young.1998,.Speir.et.al..1995)..This.swelling.
process.is.reversible.and.the.native.state.can.be.recovered.by.slowly.reducing.the.pH.to.
∼5..At.pH.above.7.0.and.in.high.ionic.strength.solutions.(∼1.M),.the.virions.disassemble.
into.dimers..The.capsid.assembly.is.not.dependent.on.a.speciic.RNA.sequence,.per.se,.and.
it. is. possible. to. reassemble. dimeric. coat. protein. into. empty,. virus-like. particles. in. vitro.
at.higher.ionic.strength.(Lavelle.et.al..2007)..It.is.assumed.that.the.high.ionic.strength.is.
needed.to.screen.the.high.positive.charge.of.the.N-terminus.that.normally.is.neutralized.by.
RNA..Although.not.required,.the.presence.of.genomic.RNA.appears.to.facilitate.assembly,.
as.functional.virions.form.relatively.fast.(Johnson.et.al..2004,.Zhao.et.al..1995)..Although.
