| 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
The middle (MID) domain of eukaryotic Argonaute (Ago) proteins and archaeal and bacterial homologues mediates the interaction with the 5'-terminal nucleotide of miRNA and siRNA guide strands. The MID domain of human Ago2 (hAgo2) is comprised of 139 amino acids with a molecular weight of 15.56 kDa. MID adopts a Rossman-like beta1-alpha1-beta2-alpha2-beta3-alpha3-beta4-alpha4 fold with a nucleotide specificity loop between beta3 and alpha3. Multiple crystal structures of nucleotides bound to hAgo2 MID have been reported, whereby complexes were obtained by soaking ligands into crystals of MID domain alone. This protocol describes a simplified one-step approach to grow well-diffracting crystals of hAgo2 MID-nucleotide complexes by mixing purified His(6)-SUMO-MID fusion protein, Ulp1 protease, and excess nucleotide in the presence of buffer and precipitant. The crystal structures of MID complexes with UMP, UTP and 2'-3' linked alpha-L-threofuranosyl thymidine-3'-triphosphate (tTTP) are presented. This article also describes fluorescence-based assays to measure dissociation constants (K(d)) of MID-nucleotide interactions for nucleoside 5'-monophosphates and nucleoside 3',5'-bisphosphates. (c) 2024 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Crystallization of Ago2 MID-nucleotide complexes Basic Protocol 2: Measurement of dissociation constant K(d) between Ago2 MID and nucleotides.
Structure and Stability of Ago2 MID-Nucleotide Complexes: All-in-One (Drop) His(6)-SUMO Tag Removal, Nucleotide Binding, and Crystal Growth.,Lei L, Harp JM, Chaput JC, Wassarman K, Schlegel MK, Manoharan M, Egli M Curr Protoc. 2024 Jun;4(6):e1088. doi: 10.1002/cpz1.1088. PMID:38923271[23]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
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- ↑ Lei L, Harp JM, Chaput JC, Wassarman K, Schlegel MK, Manoharan M, Egli M. Structure and Stability of Ago2 MID-Nucleotide Complexes: All-in-One (Drop) His(6)-SUMO Tag Removal, Nucleotide Binding, and Crystal Growth. Curr Protoc. 2024 Jun;4(6):e1088. PMID:38923271 doi:10.1002/cpz1.1088
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