title: Crystal structure reveals specific recognition of a G-quadruplex RNA by a β-turn in the RGG motif of FMRP.
abstract: Fragile X Mental Retardation Protein (FMRP) is a regulatory RNA binding protein that plays a central role in the development of several human disorders including Fragile X Syndrome (FXS) and autism. FMRP uses an arginine-glycine-rich (RGG) motif for specific interactions with guanine (G)-quadruplexes, mRNA elements implicated in the disease-associated regulation of specific mRNAs. Here we report the 2.8-Å crystal structure of the complex between the human FMRP RGG peptide bound to the in vitro selected G-rich RNA. In this model system, the RNA adopts an intramolecular K(+)-stabilized G-quadruplex structure composed of three G-quartets and a mixed tetrad connected to an RNA duplex. The RGG peptide specifically binds to the duplex-quadruplex junction, the mixed tetrad, and the duplex region of the RNA through shape complementarity, cation-π interactions, and multiple hydrogen bonds. Many of these interactions critically depend on a type I β-turn, a secondary structure element whose formation was not previously recognized in the RGG motif of FMRP. RNA mutagenesis and footprinting experiments indicate that interactions of the peptide with the duplex-quadruplex junction and the duplex of RNA are equally important for affinity and specificity of the RGG-RNA complex formation. These results suggest that specific binding of cellular RNAs by FMRP may involve hydrogen bonding with RNA duplexes and that RNA duplex recognition can be a characteristic RNA binding feature for RGG motifs in other proteins.
authors.affiliation: Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY 10016;
authors.forename: Nikita
authors.initials: N
authors.lastname: Vasilyev
authors.affiliation: Structural Biology Program, Memorial Sloan Kettering Cancer Center, NY 10065;
authors.forename: Anna
authors.initials: A
authors.lastname: Polonskaia
authors.affiliation: Laboratory of Molecular Neuro-Oncology, The Rockefeller University, New York, NY 10065;
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: Darnell
authors.affiliation: Laboratory of Molecular Neuro-Oncology, The Rockefeller University, New York, NY 10065; Howard Hughes Medical Institute, The Rockefeller University, New York, NY 10065; New York Genome Center, New York, NY, 10013.
authors.forename: Robert B
authors.initials: RB
authors.lastname: Darnell
authors.affiliation: Structural Biology Program, Memorial Sloan Kettering Cancer Center, NY 10065; pateld@mskcc.org Alexander.Serganov@nyumc.org.
authors.forename: Dinshaw J
authors.initials: DJ
authors.lastname: Patel
authors.affiliation: Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY 10016; pateld@mskcc.org Alexander.Serganov@nyumc.org.
authors.forename: Alexander
authors.initials: A
authors.lastname: Serganov
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics; D003460:Crystallization; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000737:chemistry*; D054856:G-Quadruplexes; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D023302:Protein Footprinting
chemical_list: D051860:Fragile X Messenger Ribonucleoprotein 1; C497683:FMR1 protein, human
keywords: FMRP; G-quadruplex; RGG box; RNA structure; fragile X syndrome