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PDBsum entry 3c4t
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References listed in PDB file
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Key reference
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Title
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Structural and biochemical insights into the dicing mechanism of mouse dicer: a conserved lysine is critical for dsrna cleavage.
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Authors
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Z.Du,
J.K.Lee,
R.Tjhen,
R.M.Stroud,
T.L.James.
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Ref.
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Proc Natl Acad Sci U S A, 2008,
105,
2391-2396.
[DOI no: ]
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PubMed id
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Abstract
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Dicer, an RNase III enzyme, initiates RNA interference by processing precursor
dsRNAs into mature microRNAs and small-interfering RNAs. It is also involved in
loading and activation of the RNA-induced silencing complex. Here, we report the
crystal structures of a catalytically active fragment of mouse Dicer, containing
the RNase IIIb and dsRNA binding domains, in its apo and Cd(2+)-bound forms, at
1.68- and 2.8-A resolution, respectively. Models of this structure with dsRNA
reveal that a lysine residue, highly conserved in Dicer RNase IIIa and IIIb
domains and in Drosha RNase IIIb domains, has the potential to participate in
the phosphodiester bond cleavage reaction by stabilizing the transition state
and leaving group of the scissile bond. Mutational and enzymatic assays confirm
the importance of this lysine in dsRNA cleavage, suggesting that this lysine
represents a conserved catalytic residue of Dicers. The structures also reveals
a approximately 45-aa region within the RNase IIIb domain that harbors an
alpha-helix at the N-terminal half and a flexible loop at the C-terminal half,
features not present in previously reported structures of homologous RNase III
domains from either bacterial RNase III enzymes or Giardia Dicer. N-terminal
residues of this alpha-helix have the potential to engage in minor groove
interaction with dsRNA substrates.
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Figure 1.
A schematic representation of the three classes of RNase III
enzymes. Protein domains are indicated as black rectangles.
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Figure 3.
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