J Biol Chem, Vol. 275, Issue 7, 4937-4942, February 18, 2000
In Vitro Selection of RNA Molecules That Inhibit
the Activity of Ricin A-chain*
Jay R.
Hesselberth
,
Darcie
Miller,
Jon
Robertus, and
Andrew D.
Ellington
From the Department of Chemistry and Biochemistry, University of
Texas, Austin, Texas 78712
The cytotoxin ricin disables translation by
depurinating a conserved site in eukaryotic rRNA. In vitro
selection has been used to generate RNA ligands (aptamers) specific for
the catalytic ricin A-chain (RTA). The anti-RTA aptamers bear no
resemblance to the normal RTA substrate, the sarcin-ricin loop (SRL),
and were not depurinated by RTA. An initial 80-nucleotide RNA ligand was minimized to a 31-nucleotide aptamer that contained all sequences and structures necessary for interacting with RTA. This minimal RNA
formed high affinity complexes with RTA (Kd = 7.3 nM) which could compete directly with the SRL for binding
to RTA. The aptamer inhibited RTA depurination of the SRL and could
partially protect translation from RTA inhibition. The IC50
of the aptamer for RTA in an in vitro translation assay is
100 nM, roughly 3 orders of magnitude lower than a small
molecule inhibitor of ricin, pteroic acid, and 2 orders of magnitude
lower than the best known RNA inhibitor. The novel anti-RTA aptamers
may find application as diagnostic reagents for a potential biological
warfare agent and hold promise as scaffolds for the development of
strong ricin inhibitors.
*
The costs of publication of this
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must therefore be hereby marked
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accordance with 18 U.S.C. Section
1734 solely to indicate this fact.