A phosphate-binding pocket within the platform-PAZ-connector helix cassette of human Dicer.
Publication Type:Journal Article
Source:Mol Cell, Volume 53, Issue 4, p.606-16 (2014)
Keywords:Amino Acid Sequence, Animals, Base Sequence, Cells, Cultured, Crystallography, X-Ray, DEAD-box RNA Helicases, Humans, Mice, Mice, Knockout, Molecular Sequence Data, Mutation, Phosphates, Protein Binding, Protein Structure, Secondary, Protein Structure, Tertiary, Ribonuclease III, RNA, Small Interfering, Sequence Homology, Amino Acid, Surface Plasmon Resonance
<p>We have solved two families of crystal structures of the human Dicer "platform-PAZ-connector helix" cassette in complex with small interfering RNAs (siRNAs). The structures possess two adjacently positioned pockets: a 2 nt 3'-overhang-binding pocket within the PAZ domain (3' pocket) and a phosphate-binding pocket within the platform domain (phosphate pocket). One family of complexes contains a knob-like α-helical protrusion, designated "hDicer-specific helix," that separates the two pockets and orients the bound siRNA away from the surface of Dicer, which could be indicative of a product release/transfer state. In the second complex, the helical protrusion is melted/disordered and the bound siRNA is aligned toward the surface of Dicer, suggestive of a cleavage-competent state. These structures allow us to propose that the transition from the cleavage-competent to the postulated product release/transfer state may involve release of the 5'-phosphate from the phosphate pocket while retaining the 3' overhang in the 3' pocket.</p>