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Structure of an mRNA:Repressor Complex ‐ Ferritin‐IRE: IRP1
Author(s) -
Theil Elizabeth C.,
Walden William E,
Volz Karl
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a652-b
Subject(s) - rna , aconitase , internal ribosome entry site , chemistry , ribosome , repressor , binding site , base pair , messenger rna , biology , biophysics , biochemistry , crystallography , microbiology and biotechnology , gene , enzyme , gene expression
A family of RNA structures (IRE) regulates iron trafficking/storage genes. IRE repressors (IRP1,2) are aconitase family members. IRE structures are helices terminated by a conserved pseudotriloop (CAGUGU/C/A), with an unpaired C in the helix (isolated or in a loop), that control mRNA translation (5′UTR) or mRNA turnover (3′UTR). Crystal structures of wild type and U6‐deletion ferritin H–IRE RNA (30 nt) complexed to IRP1 diffracted to 2.8 and 2.6 Å, respectively, and show mutual induced fit. U6, an unpaired base in some IRE‐RNA helices, coincides with facile IRP binding. At the RNA terminal loop site, two bases, A15, and G16, extrude into a protein cavity. All loop bases, A15 G16 and U17, have protein contacts. At the C8 binding site, the unpaired base projects from the RNA helix into an IRP pocket where protein backbone: RNA interactions dominate. In free IRE‐RNA (NMR spectroscopy) G16 and U17 are largely disordered, A15 is stacked over the C‐G base pair and the helix bend differs. The two RNA binding sites are separated by ~30 Å. In an alternative IRP1 conformer, [4Fe‐4S]‐ cytoplasmic aconitase, RNA binding residues are at the enzyme active site. Extensive domain rearrangements narrow the RNA binding cleft by 25 Å, forming the aconitase enzyme active site. Deletion of U6 mainly changes IRP:IRE interactions in the lower stem, where the largest IRE‐RNA variations occur. Phylogenetically conserved IRE‐RNA helix variations among the family members may alter protein interactions and contribute to differential binding/repression observed in vitro and in vivo. Support:NIH‐DK 20251(ECT), DK 47281 (WEW), GM47522 (KV).