Biology Reference
In-Depth Information
cluster, while the looptomiR only affected pre-miR-18, suggesting
a slightly different mechanism of action. Additionally, due to the
aptamer being selected against the entire polycistron, some
degree of miRNA specifi city is lost.
The use of aptamers to interfere with miRNA maturation in
vitro shows promise as a tool to modulate miRNA function. Such
methods allow for more specifi c means to elucidate the miRNA
processing and maturation pathways. However, in order to be truly
effective, the action of these RNA aptamers must also be demon-
strated to be functional within in vivo studies involving more com-
plex environments.
3
Manipulation of Pre-miRNA Maturation
The targeting of pre-miRNA maturation has received signifi cantly
more attention, potentially due to a greater wealth of information
surrounding both pre-miRNA precursors and their processing
enzymes (e.g., Dicer) as a result of their similarities to the siRNA
maturation pathways. Moreover, the stem-loop structure of pre-
miRNAs makes them amenable to the development of both in vivo
and in vitro assays using both small molecules and biomacromole-
cules. The processing of pre-miRNAs to mature miRNAs can also
be modulated by a variety of mechanisms including direct binding
as well as inhibition of Dicer processing.
The ability to develop specifi c non-oligonucleotide binders to
RNA is a challenging task due to the minimal chemical diversity
and secondary structure of small RNAs; however, several research-
ers have exploited both peptides and peptoids towards this goal.
Research in the Beal laboratory investigated a series of helix-
threading peptides (HTPs) harboring an intercalating heterocyclic
core and peptide appendages capable of stabilizing interactions
with a target RNA [
47
]. There are two primary advantages for
employing macrocyclic HTPs to target RNA, fi rstly that HTPs
offer a distinct orientation of peptide functional groups. This struc-
tural rigidity provides a recognition surface with limited conforma-
tional fl exibility. However, although these conformations are
limited, not all conformations confer specifi c amino acid-nucleo-
tide interactions. The second major advantage is the increased cel-
lular permeability, stability, and RNA binding affi nity of cyclic
peptides relative to their linear analogs.
HTPs were prepared by a relatively short solid-supported syn-
thesis of a protected quinoline acid containing diallyl peptide fol-
lowed by a ring closing metathesis to generate macrocyclic peptides
(Scheme
1
). Only two cyclic HTPs were reported,
7
and
8
, with
their binding properties assessed against a targeted stem-loop
RNA by ribonuclease footprinting. Although one of the resulting
3.1 Specifi c Binding
of Pre-miRNA by
Peptides and Peptoids
In Vitro
