Biomedical Engineering Reference
In-Depth Information
of.proteins,.however,.is.their.sensitivity.to.different.environmental.conditions:.tempera-
ture,.pH,.proteases,.etc..A.protein.that.is.both.durable.and.structurally.diverse.is.of.great.
interest..SP1.was.reported.to.form.highly.ordered.2D.arrays,.selectively.attach.to.different.
surfaces,.and.serve.as.a.logic.and.memory.unit.based.on.its.capability.to.attach.a.silicon.
nanoparticle.(NP).to.its.pore.
13,16,17
.Here.we.show.the.use.of.the.SP1.proteins.as.building.
blocks.for.future.nanowires,.based.on.their.extreme.stability.and.on.their.ability.to.con-
nect.gold.nanoparticle.(GNP).to.their.inner.pores,.followed.by.forming.junctions.between.
DNA.strands.or.by.self-assembly.of.nanotubes.
18
1.2 TheSP1-GNPHybrid
SP1. is. a. circular. homo-oligomeric. dodecameric. protein,. isolated. from. aspen. (
Populus
tremula
). plants.
19,20
. One. of. SP1's. great. advantages. is. its. extreme. stability.. SP1. is. a. boiling.
stable. protein. with. a. melting. temperature. of. 109°C. that. can. withstand. a. broad. range. of.
extreme.conditions,.such.as.a.wide.pH.range,.protease,.detergents,.chaotropic.agents,.and.
organic. solvents.. Its. crystal. structure. reveals. a. ring,. 11. nm. in. diameter,. with. an. inner.
pore.of.2-3.nm.and.width.of.4-5.nm.
21
.The.N.terminil.region.of.the.SP1.dodecamer.faces.
the.inner.pore.of.the.ring.and.is.tolerant.to.amino.acid.deletions.and.additions.
22
.Adding.
six-histidine.amino.acid.groups.to.each.one.of.the.12.SP1.subunits'.N.termini.led.to.the.
formation.of.a.mutant.capable.of.attaching.a.Ni-NTA-covered.gold.nanoparticle.(GNP).to.
its.inner.pore..The.interaction.of.Ni-NTA.and.histidines.is.extremely.strong,.about.10
-7
.to.
10
-13
.M..This.mutant,.called.6His-SP1,.shows.the.same.high.durability.and.boiling.resis-
tance.as.the.nonmutated.SP1.
18
.Commercially.available.1.8.nm.GNPs.covered.by.Ni-NTA.
ligands.(Nanoprobes,.Yaphank.NY.USA).were.attached.to.the.N.termini.of.the.6His-SP1..
Incubation.of.this.variant.with.Ni-NTA.GNPs.in.the.presence.of.3.M.GuHCl.(presumably.
enabling.exposure.of the.histidine.tags.by.loosening.the.protein.structure
16
).targeted.the.
GNPs.to.the.center.of.the.dodecamer.rings.(Figure 1.1)..The.diameter.of.the.Ni-NTA.GNP.
(1.8.nm).its.well.into.the.diameter.of.the.dodecamer.inner.pore.(~3.nm).
O
O
O
-
O
-
NH
N
N
??
O
R
1.8 nm
Nanogold
?
OC
H
O
N
NH
HN
CO
H
C
FIGURE 1.1
6His-SP1-GNP.hybrids..The.6His.amino.acid.addition.to.the.end.of.each.monomer.N.termini.has.high.afinity.
to.the.Ni-NTA.groups.covering.the.1.8.GNP..Addition.of.GuHCl.causes.the.exposure.of.the.N.termini.to.the.Ni
2+
.
groups,.enabling.the.formation.of.the.hybrid.
