title: The snRNP 15.5K protein folds its cognate K-turn RNA: a combined theoretical and biochemical study.
abstract: The human 15.5K protein binds to the 5' stem-loop of U4 snRNA, promotes the assembly of the spliceosomal U4/U6 snRNP, and is required for the recruitment of the 61K protein and the 20/60/90K protein complex to the U4 snRNA. In the crystallographic structure of the 15.5K-U4 snRNA complex, the conformation of the RNA corresponds to the family of kink-turn (K-turn) structural motifs. We simulated the complex and the free RNA, showing how the protein binding and the intrinsic flexibility contribute to the RNA folding process. We found that the RNA is significantly more flexible in the absence of the 15.5K protein. Conformational transitions such as the interconversion between alternative purine stacking schemes, the loss of G-A base pairs, and the opening of the K-turn occur only in the free RNA. Furthermore, the stability of one canonical G-C base pair is influenced both by the binding of the 15.5K protein and the nature of the adjacent structural element in the RNA. We performed chemical RNA modification experiments and observed that the free RNA lacks secondary structure elements, a result in excellent agreement with the simulations. Based on these observations, we propose a protein-assisted RNA folding mechanism in which the RNA intrinsic flexibility functions as a catalyst.
authors.affiliation: Department of Molecular Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany. tjovin@gwdg.de
authors.forename: Vlad
authors.initials: V
authors.lastname: Cojocaru
authors.forename: Stephanie
authors.initials: S
authors.lastname: Nottrott
authors.forename: Reinhard
authors.initials: R
authors.lastname: Klement
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Jovin
mesh_terms: D001483:Base Sequence; D006801:Humans; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D011487:Protein Conformation; D012342:RNA, Small Nuclear / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017414:Ribonucleoprotein, U4-U6 Small Nuclear / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017411:Ribonucleoproteins, Small Nuclear / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D046911:Macromolecular Substances; D012342:RNA, Small Nuclear; D011994:Recombinant Proteins; D017414:Ribonucleoprotein, U4-U6 Small Nuclear; D017411:Ribonucleoproteins, Small Nuclear; C402291:Snu13 protein, human; C405482:U4 small nuclear RNA