Biomedical Engineering Reference
In-Depth Information
The G-quadruplex formation is cation-selective. The selectivity sequence is K
+
>
NH
4
+
~Ba
2+
Li
+
.Ba
2+
can form a long-lived G-quadruplex with
TBA. However, due to the strong cation-DNA interaction, G-quadruplex was
not detected in Mg
2+
and Ca
2+
. The high formation capability of the K
+
-induced
G-quadruplex is contributed largely by the slow unfolding reaction. Interestingly,
although the Na
+
- and Li
+
-quadruplexes feature similar equilibrium properties, they
undergo radically different pathways. The Na
+
-quadruplex folds and unfolds most
rapidly, while the Li
+
-quadruplex performs both reactions at the slowest rates. The
sensitive nanopore also revealed that the cation-selective formation of the
G-quadruplex is correlated with the G-quadruplex volume, which varies with cation
species.
Cs
+
~Na
+
>
>
3.2.6 Significance and Impacts
The research on single aptamer molecule folding/unfolding properties suggests the
nanopore provide a powerful sensitive, non-covalent, label-free approach for sin-
gle-molecule manipulation, based on the principle that when a molecule folds,
unfolds or reacts in the lumen of a pore, different molecular states can characteris-
tically alter the pore conductance that can be identified. The current signatures help
to recognize these states and their transitions, making it possible to track single-
molecule folding/unfolding or reaction pathway. The nanopore method is also
applicable to other quadruplexes and their variants, including a variety of bio-
relevant intramolecular quadruplexes, such as the i-motif (quadruplexes formed by
cytidine-rich sequences) and chemically-modified quadruplexes with unique func-
tionalities. When combined with site-directed nucleotide substitution, the nanopore
method could be used to examine the contribution of each guanine to the quad-
ruplex's folding capability. Nanopores could also be used to determine the force
involved in the interaction of G-quadruplex aptamers and their targets, such as
thrombin and HIV-1 reverse transcriptase. This would further enhance the under-
standing of the molecular recognition by aptamer-target complexes. Finally, this
research may facilitate the generation of new molecular species with tunable
properties for nano-construction and the manufacture of biosensors.
3.3 Single Molecule Biosensing with a Robust
Nanopore Biochip
The best-learned and most useful property of aptamers is their ability to specifically
bind targets with high affinity, which renders aptamers unique sensors for ultra-
sensitive bio-detection. For example, due to the high affinity in nanomolar (nM),
a number of aptamer-based techniques for thrombin detection have been pro-
posed, such as sensitive electrochemical technique [
124
] and molecular beacon
Search WWH ::
Custom Search