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Publication Abstract from PubMed

Human antigen R (HuR) functions as a major post-transcriptional regulator of gene expression through its RNA-binding activity. HuR is composed by three RNA recognition motifs, namely RRM1, RRM2, and RRM3. The two N-terminal RRM domains are disposed in tandem and contribute mostly to HuR interaction with adenine and uracil-rich elements (ARE) in mRNA. Here, we used a combination of NMR and electrospray ionization-ion mobility spectrometry-mass spectrometry (ESI-IMS-MS) to characterize the structure, dynamics, RNA recognition, and dimerization of HuR RRM1. Our solution structure reveals a canonical RRM fold containing a 19-residue, intrinsically disordered N-terminal extension, which is not involved in RNA binding. NMR titration results confirm the primary RNA-binding site to the two central beta-strands, beta1 and beta3, for a cyclooxygenase 2 (Cox2) ARE I-derived, 7-nucleotide RNA ligand. We show by (15)N relaxation that, in addition to the N- and C-termini, the beta2-beta3 loop undergoes fast backbone dynamics (ps-ns) both in the free and RNA-bound state, indicating that no structural ordering happens upon RNA interaction. ESI-IMS-MS reveals that HuR RRM1 dimerizes, however dimer population represents a minority. Dimerization occurs via the alpha-helical surface, which is oppositely orientated to the RNA-binding beta-sheet. By using a DNA analog of the Cox2 ARE I, we show that DNA binding stabilizes HuR RRM1 monomer and shifts the monomer-dimer equilibrium toward the monomeric species. Altogether, our results deepen the current understanding of the mechanism of RNA recognition employed by HuR.

Oligomeric transition and dynamics of RNA binding by the HuR RRM1 domain in solution.,Lixa C, Mujo A, de Magalhaes MTQ, Almeida FCL, Lima LMTR, Pinheiro AS J Biomol NMR. 2018 Dec;72(3-4):179-192. doi: 10.1007/s10858-018-0217-y. Epub 2018, Dec 8. PMID:30535889^[2]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.