title: [Mg2+ ions affect the structure of the central domain of the 18S rRNA in the vicinity of the ribosomal protein S13 binding site].
abstract: It is known that Mg2+ ions at high concentrations stabilize the structure of the 16S rRNA in a conformation favorable for binding to the ribosomal proteins in the course of the eubacterial 30S ribosomal subunits assembly in vitro. Effect of Mg2+ on the formation of the 18S rRNA structure at the 40S subunit assembly remains poorly explored. In this paper, we show that the sequentional increase of the Mg2+ concentration from 0.5 mM to 20 mM leads to a significant decrease of the affinity of recombinant human ribosomal protein S13 (rpS13e) to a RNA transcript corresponding to the central domain fragment of the 18S rRNA (18SCD). The regions near the rpS13e binding site in 18SCD (including the nucleotides of helices H20 and H22), whose availabilities to hydroxyl radicals were dependent on the Mg2+ concentration, were determined. It was found that increase of the concentrations of Mg2+ results in the enhanced accessibilities of nucleotides G933-C937 and C1006-A1009 in helix H22 and reduces those of nucleotides A1023, A1024, and A1028-S1026 in the helix H20. Comparison of the results obtained with the crystallographic data on the structure of the central domain of 18S rRNA in the 40S ribosomal subunit led to conclusion that increase of Mg2+ concentrations results in the reorientation of helices H20 and H24 relatively helices H22 and H23 to form a structure, in which these helices are positioned the same way as in 40S subunits. Hence, saturation of the central domain of 18S rRNA with coordinated Mg2+ ions causes the same changes in its structure as rpS13e binding does, and leads to decreasing of this domain affinity to the protein.
authors.forename: A V
authors.initials: AV
authors.lastname: Ivanov
authors.forename: A A
authors.initials: AA
authors.lastname: Malygin
authors.forename: G G
authors.initials: GG
authors.lastname: Karpova
mesh_terms: D001665:Binding Sites / Q000187:drug effects; D004926:Escherichia coli / Q000235:genetics; D006801:Humans; D007477:Ions / Q000737:chemistry; D008274:Magnesium / Q000737:chemistry / Q000494:pharmacology*; D009690:Nucleic Acid Conformation / Q000187:drug effects; D012337:RNA, Ribosomal, 18S / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism; D054682:Ribosome Subunits, Small, Eukaryotic / Q000737:chemistry / Q000235:genetics / Q000473:pathology
chemical_list: D007477:Ions; D012337:RNA, Ribosomal, 18S; C047013:RPS13 protein, human; D012269:Ribosomal Proteins; D008274:Magnesium