Poly[μ2-aqua-(μ3-2,5-dichloro­benzene­sulfonato)sodium]

In the title compound, [Na(C6H3Cl2O3S)(H2O)]n, the NaI ion is penta­coordinated by three dichloro­benzene­sulfonate anions and two water mol­ecules, forming a distorted trigonal-bipyramidal geometry. The NaI ions are bridged by the sulfonate groups and the water mol­ecules, leading to a polymeric layer structure parallel to the bc plane in which O—H⋯O hydrogen bonds are observed

Triethyl­ammonium 4-nitro­benzene­sulfonate

In the anion of the title molecular salt, C6H16N+·C6H4O5S−, the nitro group is twisted slightly from the benzene ring, making a dihedral angle of 3.16 (10)°. In the crystal structure, the cations and anions are linked into a two-dimensional network parallel to the ab plane by C—H⋯O and N—H⋯O hydrogen bonds

Multiple segmental and selective isotope labeling of large RNA for NMR structural studies

Multiple segmental and selective isotope labeling of RNA with three segments has been demonstrated by introducing an RNA segment, selectively labeled with 13C9/15N2/2H(1′, 3′, 4′, 5′, 5′′)-labeled uridine residues, into the central position of the 20 kDa ε-RNA of Duck Hepatitis B Virus. The RNA molecules were produced via two efficient protocols: a two-step protocol, which uses T4 DNA ligase and T4 RNA ligase 1, and a one-pot protocol, which uses T4 RNA ligase 1 alone. With T4 RNA ligase 1 all not-to-be-ligated termini are usually protected to prevent formation of side products. We show that such labor-intensive protection of termini is not required, provided segmentation sites can be chosen such that the segments fold into the target structure or target-like structures and thus are not trapped into stable alternate structures. These sites can be reliably predicted via DINAMelt. The simplified NMR spectrum provided evidence for the presence of a U28 H3-imino resonance, previously obscured in the fully labeled sample, and thus of the non-canonical base pair U28:C37. The demonstrated multiple segmental labeling protocols are generally applicable to large RNA molecules and can be extended to more than three segments

Resolving fast and slow motions in the internal loop containing stem-loop 1 of HIV-1 that are modulated by Mg(2+) binding: role in the kissing–duplex structural transition

Stem loop 1 (SL1) is a highly conserved hairpin in the 5′-leader of the human immunodeficiency virus type I that forms a metastable kissing dimer that is converted during viral maturation into a stable duplex with the aid of the nucleocapsid (NC) protein. SL1 contains a highly conserved internal loop that promotes the kissing–duplex transition by a mechanism that remains poorly understood. Using NMR, we characterized internal motions induced by the internal loop in an SL1 monomer that may promote the kissing–duplex transition. This includes micro-to-millisecond secondary structural transitions that cause partial melting of three base-pairs above the internal loop making them key nucleation sites for exchanging strands and nanosecond rigid-body stem motions that can help bring strands into spatial register. We show that while Mg(2+) binds to the internal loop and arrests these internal motions, it preserves and/or activates local mobility at internal loop residues G272 and G273 which are implicated in NC binding. By stabilizing SL1 without compromising the accessibility of G272 and G273 for NC binding, Mg(2+) may increase the dependence of the kissing–duplex transition on NC binding thus preventing spontaneous transitions from taking place and ensuring that viral RNA and protein maturation occur in concert

Review NMR studies of RNA dynamics and structural plasticity using NMR residual dipolar couplings

An increasing number of RNAs are being discovered that perform their functions by undergoing large changes in conformation in response to a variety of cellular signals, including recognition of proteins and small molecular targets, changes in temperature, and RNA synthesis itself. The measurement of NMR residual dipolar couplings (RDCs) in partially aligned systems is providing new insights into the structural plasticity of RNA through combined characterization of large-amplitude collective helix motions and local flexibility in noncanonical regions over a wide window of biologically relevant timescales (<milliseconds). Here, we review RDC methodology for studying RNA structural dynamics and survey what has been learnt thus far from application of these methods. Future methodological challenges are also identified. © 2007 Wiley Periodicals, Inc. Biopolymers 86: 384–402, 2007. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at [email protected] Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/56044/1/20765_ftp.pd