Chemistry Reference
In-Depth Information
Initial pool of
DNA/RNA
Selections
using only Co
2+
DNA/RNA with
Co
2+
activity
Positive
Selection
Negative
Selection
Selection
using only Co
2+
Selection with a 'metal
soup' containing
competing metal ions
Remove sequences that are
active with other metal ions
High Co
2+
activity,
but with low Co
2+
selectivity
Continue Co
2+
selection
High Co
2+
activity with
high Co
2+
selectivity
Figure 14.3
Schemes of parallel selections of Co(II)-dependent DNAzymes with and without
negative selection. (Yi Lu, Prof; New Transition-Metal-Dependent DNAzymes as Effi cient
Endonucleases and as Selective Metal Biosensors.
Chemistry - A European Journal
, 2002,
8
,
4589-4596. Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission.)
investigated including Ca(II), Mg(II) and Cd(II), and cleavage activity in the pres-
ence of Mn(II) was minimum. This result shows the effectiveness of negative selec-
tion in improving specifi city of DNAzymes and further demonstrates that
in vitro
selection is a powerful and versatile method for generating DNA/RNAzymes with
the desired properties by carefully designed strategies and well-controlled conditions.
14.4 Understanding Nucleic Acid Enzyme -Metal Ion Interactions
Compared to ribozymes and protein enzymes, the understanding of the detailed
interaction between metal ions and DNAzymes and how metal ions affect the activi-
ties of the DNAzymes remains very limited. For instance, while many three-
dimensional structures of ribozymes and protein enzymes are available,
51 - 54
only one
DNAzyme structure has been reported.
55
Yet this structure is not the enzyme's
active conformation, and thus provides limited insight into the enzymatic activity.
Furthermore, whereas a great deal of knowledge has been available on the roles of
metal ions in protein enzymes, much less is known about that in nucleic acids. As a
result, understanding of the structure and function of metal ions in DNA/RNAzymes
