| Structural highlights
Function
[AGO2_HUMAN] Required for RNA-mediated gene silencing (RNAi) by the RNA-induced silencing complex (RISC). The 'minimal RISC' appears to include EIF2C2/AGO2 bound to a short guide RNA such as a microRNA (miRNA) or short interfering RNA (siRNA). These guide RNAs direct RISC to complementary mRNAs that are targets for RISC-mediated gene silencing. The precise mechanism of gene silencing depends on the degree of complementarity between the miRNA or siRNA and its target. Binding of RISC to a perfectly complementary mRNA generally results in silencing due to endonucleolytic cleavage of the mRNA specifically by EIF2C2/AGO2. Binding of RISC to a partially complementary mRNA results in silencing through inhibition of translation, and this is independent of endonuclease activity. May inhibit translation initiation by binding to the 7-methylguanosine cap, thereby preventing the recruitment of the translation initiation factor eIF4-E. May also inhibit translation initiation via interaction with EIF6, which itself binds to the 60S ribosomal subunit and prevents its association with the 40S ribosomal subunit. The inhibition of translational initiation leads to the accumulation of the affected mRNA in cytoplasmic processing bodies (P-bodies), where mRNA degradation may subsequently occur. In some cases RISC-mediated translational repression is also observed for miRNAs that perfectly match the 3' untranslated region (3'-UTR). Can also up-regulate the translation of specific mRNAs under certain growth conditions. Binds to the AU element of the 3'-UTR of the TNF (TNF-alpha) mRNA and up-regulates translation under conditions of serum starvation. Also required for transcriptional gene silencing (TGS), in which short RNAs known as antigene RNAs or agRNAs direct the transcriptional repression of complementary promoter regions.[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22]
Publication Abstract from PubMed
Short interfering RNAs (siRNAs) are promising therapeutics that make use of the RNA interference (RNAi) pathway, but liabilities arising from the native RNA structure necessitate chemical modification for drug development. Advances in the structural characterization of components of the human RNAi pathway have enabled structure-guided optimization of siRNA properties. Here we report the 2.3 A resolution crystal structure of human Argonaute 2 (hAgo2), a key nuclease in the RNAi pathway, bound to an siRNA guide strand bearing an unnatural triazolyl nucleotide at position 1 (g1). Unlike natural nucleotides, this analogue inserts deeply into hAgo2's central RNA binding cleft and thus is able to modulate pairing between guide and target RNAs. The affinity of the hAgo2-siRNA complex for a seed-only matched target was significantly reduced by the triazolyl modification, while the affinity for a fully matched target was unchanged. In addition, siRNA potency for off-target repression was reduced (4-fold increase in IC50) by the modification, while on-target knockdown was improved (2-fold reduction in IC50). Controlling siRNA on-target versus microRNA (miRNA)-like off-target potency by projection of substituent groups into the hAgo2 central cleft from g1 is a new approach to enhance siRNA selectivity with a strong structural rationale.
Structure-Guided Control of siRNA Off-Target Effects.,Suter SR, Sheu-Gruttadauria J, Schirle NT, Valenzuela R, Ball-Jones AA, Onizuka K, MacRae IJ, Beal PA J Am Chem Soc. 2016 Jul 20;138(28):8667-9. doi: 10.1021/jacs.6b06137. Epub 2016, Jul 12. PMID:27387838[23]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
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- ↑ Suter SR, Sheu-Gruttadauria J, Schirle NT, Valenzuela R, Ball-Jones AA, Onizuka K, MacRae IJ, Beal PA. Structure-Guided Control of siRNA Off-Target Effects. J Am Chem Soc. 2016 Jul 20;138(28):8667-9. doi: 10.1021/jacs.6b06137. Epub 2016, Jul 12. PMID:27387838 doi:http://dx.doi.org/10.1021/jacs.6b06137
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