Biomedical Engineering Reference
In-Depth Information
This. chapter. focuses. on. the. use. of. viruses,. or. virus-based. structures. for. applications. in.
nanobiotechnology..Over.the.last.two.decades,.bioderived.nanomaterials.have.gained.much.
interest;. where. in. this. ield,. viruses. represent. a. unique,. self-assembling. multifunctional.
platform..Viruses.have,.for.instance,.been.used.as.biological.templates,.delivery.vessels,.and.
nanoscale.catalysts.for.chemical.reactions.or.materials.synthesis..Here,.we.will.irst.present.
a.brief.description.of.viruses,.their.structure,.and.lifecycle.in.order.to.familiarize.the.reader.
with. the. topic.. This. will. be. followed. by. a. comprehensive. overview. of. six. different. virus.
systems.that.have.been.extensively.studied.and.engineered.for.use.in.nanobiotechnology..
We. think. these. six. examples. provide. the. reader. with. a. well-rounded. representation. of.
the.accomplishments.that.have.been.achieved.within.this.exciting.scientiic.research.area..
Within.each.subsection,.we.will.provide.some.background.on.the.virus,.where,.in.addition.
to.the.various.nanobio-applications.that.have.been.explored.for.each.particular.system,.we.
will.also.describe.some.strategies.that.have.been.used.to.modify.the.virus.properties.
7.1 Introduction to Viruses
7.1.1 Overview
A.virus.is.deined.as.an.infectious.agent.that.requires.the.cellular.machinery.of.its.infected.
host. to. replicate. and. generate. progeny.. They. are. highly. functional. natural. “nanoma-
chines,”.whose.main.purpose.is.to.transfer.their.genetic.material.to.a.host.cell,.replicate,.
and.escape.to.infect.more.hosts..They.are.incredibly.robust,.the.most.abundant.biological.
organisms. on. the. planet. and. are. capable. of. infecting. almost. every. organism. known. to.
science.(Edwards.and.Rohwer.2005)..Additionally,.they.are.the.smallest.known.organisms.
capable.of.replication..However,.they.have.no.metabolism.of.their.own;.rather.they.must.
hijack.the.cellular.mechanisms.of.the.host.and.redirect.them.for.their.own.purposes.(Knipe.
et.al..2007)..Viruses.are.entirely.dependent.on.the.host.cell.for.survival..Furthermore,.most.
virus.infections.are.species-speciic,.that.is,.they.are.only.able.to.infect.a.narrow.range.of.
plants,.animals,.bacteria,.or.fungi.to.reproduce..The.size,.structure,.and.genetic.restraints.
placed.on.viruses.by.eons.of.evolutionary.pressures.have.resulted.in.very.little.waste.with.
respect.to.their.genetic.material,.structure,.and.life.cycle.
The.viral.life.cycle.can.be.generalized.by.three.or.four.phases:.(1).viral.entry,.(2).rep-
lication,.(3).shedding,.and/or.(4).latency..Each.phase.in.the.viral.life.cycle.consists.of.a.
multitude. of. speciic. interactions. at. the. nanoscale,. making. them. prime. candidates. for.
use. as. biotemplates. or. nanoengineering. scaffolds,. as. will. be. discussed. later.. Infection.
begins.with.viral.entry.into.the.host.cell..This.requires.the.binding.of.viral.attachment.
proteins.to.receptors.on.the.target.cell.surface,.or.fusion.of.the.viral.envelope.to.the.cell.
membrane,.followed.by.internalization.of.the.virus's.genetic.material,.and.depending.on.
the.virus,.replication.proteins..During.replication,.the.virus.takes.control.of.the.host.cell's.
machinery,. directing. it. to. synthesize. copies. of. viral. nucleic. acids. and. proteins,. which.
then.self-assemble.into.a.functional.virion..Phase.three.consists.of.the.escape.of.the.viral.
progeny.from.the.host.cell..The.fourth.phase—latency—occurs.when.under.certain.cir-
cumstances,.such.as.evasion.of.host.cell.defense.mechanisms,.the.virus.may.incorporate.
its.genetic.material.into.that.of.the.host,.and.wait.for.more.favorable.conditions.to.repli-
cate.(Knipe.et.al..2007).
The.structure.of.most.viruses.can.be.described.simply.as.a.protein.shell,.better.known.as.
a.capsid,.that.surrounds.and.protects.the.genetic.material.during.its.transfer.from.one.host.
