Biomedical Engineering Reference
In-Depth Information
Klps. are. also. regulatable,. including. the. use. of. monastrol. (ispinesib). to. deactivate. the.
kinesin-5.family.of.Klps,.antibodies.or.aptamers.(Shi.et.al.,.2007;.Syed.and.Pervaiz,.2010)..
Mixed.motor.velocities.must.also.be.considered.(Larson.et.al..2010).
A. inal. challenge. regarding. biosynthetic. devices. concerns. the. ability. to. monitor.
the. process. in. real. time. without. disturbing. the. system.. Within. the. ield. of. microscopy,.
particularly. in. terms. of. tracking. dynamics,. increased. sensitivity. from. high. to. super.
resolution. microscopy. is. enabling. new. discoveries. at. the. nanoscale.. However,. most. of.
these.capabilities.require.the.use.of.transmitted.light.and.silicon.oxide.(glass).as.the.optical.
surface..Functionalized.surfaces.and.patterns.that.are.generated.during.integrated.circuit.
fabrication. are. not. transparent. for. imaging.. Hybrid. devices. that. combine. both. silicon.
oxide.and.integrated.circuit.surfaces.in.a.patchwork.design.represent.a.possible.solution.
4.4.3 Molecular Motors in Transport Designs
Functional.devices.that.incorporate.transport.and.assembly.of.features.in.a.primarily.self-
assembling.platform.will.in.the.future.be.used.to.replace.current.nanoelectromechanical.
systems. (NEMS). and. microelectromechanical. systems. (MEMS). devices. (Bhushan,. 2008).
in.which.the.required.nanoscale.platform.does.not.allow.practical.physical.manipulation..
Currently,. the. ield. is. in. its. infancy. and. simple. primary. design. questions. are. being.
addressed,. which. include. the. following:. (1). What. is. being. transported. and. by. what.
motor. mechanism?. (2). How. will. the. cargo. be. eficiently. loaded. and. unloaded?. (3). Will.
the.progression/speed.of.the.transporter.be.constant.or.need.to.be.regulated?.(4).By.what.
means.will.the.transporter.be.guided?.Klp.molecular.motors.have.been.analyzed.in.vitro.
by. primarily. two. approaches. that. are. directly. applicable. to. design. of. nanoengineered.
devices.(Vale,.1985;.Block,.1995;.Figure.4.3.and.4.4)..In.the.irst.approach,.the.microtubule.
ilament.is.attached.to.the.surface.as.a.ixed.track.for.the.Klp..A.limitation.of.this.approach.
is.the.critical.need.to.maintain.suficient.microtubule.length.for.the.process..An.alternative.
strategy. uses. a. gliding. ilament. approach. in. which. Klps. are. ixed. to. a. surface. through.
modiication. of. their. stalk. or. tail. domains,. which. allows. the. motor. domains. to. shuttle.
microtubule. ilaments. along. with. any. microtubule-attached. cargo.. This. has. similarly.
been.done.with.actin.and.myosins.(Kron.and.Spudich,.1986)..Motor.density.on.the.surface.
must.be.suficient.to.retain.the.microtubule.cargo.and.prevent.it.from.loating.away..By.
optimizing. parameters. of. pH,. ionic. strength,. Mg
2+
,. and. temperature,. the. microtubule-
gliding.across.kinesin-covered.glass.slides.can.be.improved.(Böhm.et.al.,.2001)..Generally,.
gliding. requires. at. least. three. motors. per. microtubule. and. will. vary. depending. on. the.
processive.capability.of.the.motor.protein.used.
When.attaching.motors.to.surfaces,.there.are.three.steps.that.typically.are.followed:.
(1). adsorption. of. a. preventive. monolayer. onto. the. substrate,. such. as. casein. or. albu-
min,.to.help.stabilize.the.motor.proteins.from.denaturation;.(2).attachment.of.selected.
motors.onto.the.prepared.surface;.and.(3).addition.and.dynamic.attachment.of.the.shut-
tles.(microtubules).into.the.system..No.matter.what.strategy.is.used,.the.monitoring.of.
the. events. is. critical. to. evaluation. and. remains. a. signiicant. challenge.. Fluorescence.
microscopy.of.tagged.proteins.has.typically.been.used.for.dynamic.imaging.of.motil-
ity.events.along.with.more.recent.use.of.quantum.dots.(Chan.et.al.,.2002;.Reiman.and.
Manninen,. 2002).. The. key. is. to. apply. luorescent. signals. that. will. not. signiicantly.
impede.function..In.living.cells,.luorescent.tags.have.evolved.from.green.luorescent.
protein.(GFP).and.its.variants.to.smaller.polypeptide.tags.that.have.reduced.functional.
effects.(Zhang.et.al.,.2002).
