Biomedical Engineering Reference
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lowed to self-assemble around the tethered proteins.
237
To this end,
a recombinant membrane protein is engineered to bear a stretch of
six consecutive histidine residues. A gold surface is then function-
alized by attaching a molecule terminated with a nitrilotriacetic
(NTA) moiety at one end and with a sulfhydryl group for anchor-
ing to gold at the other end. Complexation of Ni
2+
ions to both the
NTA functionality and the histidines of the stretch causes the pro-
tein to be anchored to the gold surface from its solution in deter-
gent, as shown in
Fig. 23
. To retain full functional integrity, the
membrane protein is incorporated into a lipid bilayer. For this pur-
pose, the protein layer tethered to gold is mixed with detergent-
destabilized lipid vesicles of DMPC. By removing the detergent
Figure 23. Adsorption of cytochrome
c
oxidase on the Ni-NTA modified Au sur-
face via the His-tag at the C-terminus of subunit I. Two nitrogen atoms of the imid-
azole rings from two of the histidines of the His stretch coordinate the Ni
2+
ion. The
coordinating histidines residues are not necessarily adjacent in the primary se-
quence, as drawn in the figure. (Reprinted from Ref.
237
with kind permission from
the American Chemical Society.)
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