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Carbon-Binding Designer Proteins that Discriminate between sp2- and sp3‑Hybridized Carbon Surfaces
journal contribution
posted on 2013-04-16, 00:00 authored by Brandon
L. Coyle, Marco Rolandi, François BaneyxRobust and simple strategies to directly
functionalize graphene-
and diamond-based nanostructures with proteins are of considerable
interest for biologically-driven manufacturing, biosensing, and bioimaging.
Here, we identify a new set of carbon-binding peptides that vary in
overall hydrophobicity and charge and engineer two of these sequences
(Car9 and Car15) within the framework of E. coli thioredoxin
1 (TrxA). We develop purification schemes to recover the resulting
TrxA derivatives in a soluble form and conduct a detailed analysis
of the mechanisms that underpin the interaction of the fusion proteins
with carbonaceous surfaces. Although equilibrium quartz crystal microbalance
measurements show that TrxA::Car9 and TrxA::Car15 have similar affinities
for sp2-hybridized graphitic carbon (Kd = 50 and 90 nM, respectively), only the latter protein
is capable of dispersing carbon nanotubes. Further investigation by
surface plasmon resonance and atomic force microscopy reveals that
TrxA::Car15 interacts with sp2-bonded carbon through a
combination of hydrophobic and π–π interactions
but that TrxA::Car9 exhibits a cooperative mode of binding that relies
on a combination of electrostatics and weaker π stacking. Consequently,
we find that TrxA::Car9 binds equally well to sp2- and
sp3-bonded (diamondlike) carbon particles whereas TrxA::Car15
is capable of discriminating between the two carbon allotropes. Our
results emphasize the importance of understanding both bulk and molecular
recognition events when exploiting the adhesive properties of solid-binding
peptides and proteins in technological applications.
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Keywords
carbon allotropesfusion proteinsrecognition eventscarbon particleslatter proteincarbon nanotubespurification schemescarbonaceous surfacesfunctionalize graphenesurface plasmon resonancecoli thioredoxin 1equilibrium quartz crystal microbalance measurements showforce microscopyTrxA derivativesCar 9sp90 nM