Biomedical Engineering Reference
In-Depth Information
and coworkers' use of a TASP strategy for design of metalloproteins is
described below (Section 6.4). The position of the ligands that will
coordinate the metal ion is crucial; however, the positioning of additional
functional groups close to the coordination site may also be important.
Coordination of Zn
2
รพ
typically requires three His imidazole ligands or a
Cys
2
His
2
binding site. Pecoraro and coworkers have focused on
Cys-containing sequences that bind mercury. Proteins have been engi-
neered which fold to provide a heme binding site, thus creating artificial
heme proteins [80,91,92]. DeGrado and coworkers designed a 4-helix
bundle (four copies of the peptide in Table 6.2, entry 1) which bound two
DPP-FE heme-like cofactor by complexation to His moieties [93]. Also,
iron-sulfur (Fe
4
S
4
) clusters have been engineered into proteins [94-96].
Table 6.2 List of some a-helical sequences (helix1-turn-helix2 topology) used in
the
de novo
design of metal-ion binding helix bundles [101,102]
Entry
Name
Sequence
1
SLEEALQEAQQTAQEAQQALQKGQQAFQKFQKYG
2
DF1
DYLRELLKLELQAIKQYREALEYV
KLPVLAKILEDEEKHIEWLETING
3
DF2
MDYLRELYKLEQQAMKLYREASEYV GD
PVLAKILEDEEKHIEWLETING
4
DF2t
MDYLRELYKLEQQAMKLYREASE KARN
PEKKSVLAKILEDEEKHIEWLETING
Metal-ion binding sites have been incorporated into the
de novo
protein a
4
. A His
3
binding site was engineered into a
4
[97,98], as was a
Cys
2
His
2
binding site [99].
Lombardi, DeGrado and coworkers have designed a series of di-iron
(III) proteins formed from antiparallel dimers of helix1-turn-helix2-type
sequences (Table 6.2, entries 2-4) [100,101].
De novo
-designed metalloproteins based on b-sheet secondary struc-
tures were achieved in a rubredoxin mimic, which bound Fe(II/III) in a
Cys
4
site formed by dimerization [102].
6.3.4
Fluorous Interactions
Proteins containing fluorous side chains were first used in
19
F-NMR
studies [103]. However, in a visionary paper, Marsh described the
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