title: Conformational flexibility in RNA: the role of dihydrouridine.
abstract: In order to further understand the structural role of the modified nucleoside dihydrouridine in RNA the solution conformations of Dp and ApDpA were analyzed by one- and two-dimensional proton NRM spectroscopy and compared with those of the related uridine-containing compounds. The analyses indicate that dihydrouridine significantly destabilizes the C3'-endo sugar conformation associated with base stacked, ordered, A-type helical RNA. Equilibrium constants (Keq = [C2'-endo]/[C3'-endo]) for C2'-endo-C3'-endo interconversion at 25 degrees C for Dp, the 5'-terminal A of ApDpA and D in ApDpA are 2.08, 1.35 and 10.8 respectively. Stabilization of the C2'-endo form was shown to be enhanced at low temperature, indicating that C2'-endo is the thermodynamically favored conformation for dihydrouridine. DeltaH values show that for Dp the C2'-endo sugar conformation is stabilized by 1.5 kcal/mol compared with Up. This effect is amplified for D in the oligonucleotide ApDpA and propagated to the 5'-neighboring A, with stabilization of the C2'-endo form by 5.3 kcal/mol for D and 3.6 kcal/mol for the 5'-terminal A. Post-transcriptional formation of dihydrouridine therefore represents a biological strategy opposite in effect to ribose methylation, 2-thiolation or pseudouridylation, all of which enhance regional stability through stabilization of the C3'-endo conformer. Dihydrouridine effectively promotes the C2'-endo sugar conformation, allowing for greater conformational flexibility and dynamic motion in regions of RNA where tertiary interactions and loop formation must be simultaneously accommodated.
authors.affiliation: Department of Biochemistry, University of Utah, Salt Lake City, 84112 USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Dalluge
authors.forename: T
authors.initials: T
authors.lastname: Hashizume
authors.forename: A E
authors.initials: AE
authors.lastname: Sopchik
authors.forename: J A
authors.initials: JA
authors.lastname: McCloskey
authors.forename: D R
authors.initials: DR
authors.lastname: Davis
mesh_terms: D004355:Drug Stability; D004926:Escherichia coli / Q000737:chemistry / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D009690:Nucleic Acid Conformation; D009843:Oligoribonucleotides / Q000138:chemical synthesis / Q000737:chemistry; D012313:RNA / Q000737:chemistry* / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D012329:RNA, Bacterial / Q000737:chemistry / Q000378:metabolism; D012996:Solutions; D013816:Thermodynamics; D014529:Uridine / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D009843:Oligoribonucleotides; D012329:RNA, Bacterial; D012996:Solutions; C010922:5,6-dihydrouridine; D012313:RNA; D014529:Uridine