title: G quadruplex RNA structures in PSD-95 mRNA: potential regulators of miR-125a seed binding site accessibility.
abstract: Fragile X syndrome (FXS) is the most common inherited form of intellectual disability caused by the CGG trinucleotide expansion in the 3'-untranslated region of the FMR1 gene on the X chromosome, that silences the expression of the Fragile X mental retardation protein (FMRP). FMRP has been shown to bind to a G-rich region within the PSD-95 mRNA which encodes for the postsynaptic density protein 95 (PSD-95), and together with the microRNA miR-125a, to play an important role in the reversible inhibition of the PSD-95 mRNA translation in neurons. The loss of FMRP in Fmr1 KO mice disables this translation control in the production of the PSD-95 protein. Interestingly, the miR-125a binding site on PSD-95 mRNA is embedded in the G-rich region bound by FMRP and postulated to adopt one or more G quadruplex structures. In this study, we have used different biophysical techniques to validate and characterize the formation of parallel G quadruplex structures and binding of miR-125a to its complementary sequence located within the 3' UTR of PSD-95 mRNA. Our results indicate that the PSD-95 mRNA G-rich region folds into alternate G quadruplex conformations that coexist in equilibrium. miR-125a forms a stable complex with PSD-95 mRNA, as evident by characteristic Watson-Crick base-pairing that coexists with one of the G quadruplex forms, suggesting a novel mechanism for G quadruplex structures to regulate the access of miR-125a to its binding site.
authors.affiliation: Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282, USA.
authors.forename: Snezana
authors.initials: S
authors.lastname: Stefanovic
authors.affiliation: Department of Cell Biology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Bassell
authors.affiliation: Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282, USA mihailescum@duq.edu.
authors.forename: Mihaela Rita
authors.initials: MR
authors.lastname: Mihailescu
mesh_terms: D020413:3' Untranslated Regions; D020029:Base Pairing; D001483:Base Sequence; D001665:Binding Sites; D000076122:Disks Large Homolog 4 Protein; D005600:Fragile X Syndrome / Q000235:genetics; D054856:G-Quadruplexes; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics*; D035683:MicroRNAs / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics*; D013816:Thermodynamics
chemical_list: D020413:3' Untranslated Regions; C501444:DLG4 protein, human; D000076122:Disks Large Homolog 4 Protein; D047908:Intracellular Signaling Peptides and Proteins; C531888:MIRN125 microRNA, human; D008565:Membrane Proteins; D035683:MicroRNAs; D012333:RNA, Messenger
keywords: Fragile X; PSD-95 mRNA; miR-125a