Chemistry Reference
In-Depth Information
Figure 1.5
Mn
2+
induced line-broadening of G-H8 resonances of the Dickerson-Drew
duplex [d(5
-C
1
G
2
C
3
G
4
A
5
A
6
T
7
T
8
C
9
G
10
C
11
G
12
)]
2
. G
4
(open squares), G
10
(fi lled squares). The
circles represent the overlapping G
2
and G
12
resonances
7
′
the minor groove (see discussion below). The amount of broadening was consistent
with inner sphere coordination to G-N7. The binding to guanine by 3d transition
metals was not surprising, considering the differences in thermodynamic stability of
the corresponding complexes of the nucleoside and nucleotide monomers.
32
However, the sequence-selective metal binding pattern manifested through the
apparent preference for G
4
rather than the residues G
2
, G
10
or G
12
, was highly
unexpected.
Further NMR spectroscopic evidence for apparent sequence-selective metal
binding to DNA is presented for the duplex d(G
1
C
2
C
3
G
4
A
5
T
6
A
7
T
8
C
9
G
10
G
11
C
12
)
(seq. II) containing the
Eco -
RV recognition sequence GATATC.
8
The 1D spectra with
and without MnCl
2
, shown in Figure 1.6, exhibit differential G-H8 line-broadening
in the order: G
10
G
11
. It is evident that the exposed terminal residues
both in sequence II and the previous sequence I, although offering favourable acces-
sibility, are not the preferred binding sites. One may also notice that the A
5
- H2 and
A
7
-H2 protons, residing in the minor groove, are completely unaffected.
A systematic search for a selectivity pattern was initiated by design-
ing three self-complementary sequences: [d(TATGGTACCATA)]
2
(III),
[d(TATGGATCCATA)]
2
(IV) and [d(TATGGCCATA)]
2
(V), where the central
triplet is GGX (X = A, T or C).
10
Mn
2+
- induced line - broadening for G - H8 versus
r = [Mn
2+
]/[duplex] is plotted in Figure 1.7 a - c. The line - broadening of G - H8 for
the 5
>
G
4
>>
G
1
∼
-G is practically the same for all three sequences. However, the line-
broadening of 3
′
′
-G-H8 is seen to depend on the adjacent residue X following a
