Biomedical subjects

Lukasz Bielecki

Publications and source records attributed to Lukasz Bielecki.

7 recordsLinked to original sources

PubMed2006

High-throughput method for the prediction of low-resolution, three-dimensional RNA structures.

Our aim is the high-throughput prediction of three-dimensional RNA structures at low resolution to answer questions posed by the RNA molecular biology. The strategy presented here is based on a computer program, called 3D-RNApredict, which implements and converts various structural data (RNA secondary structure, RNA motifs coordinates, experimental data) to create the input to the CYANA program (torsion-angle dynamics algorithm, TAD) which provides a fast engine for the 3D RNA structure calculation. The resultant RNA structure is refined using the X-PLOR program. The approach is amenable to automatization. Current predictions involve HIV-2 leader RNA domains and the sets of bacterial ncRNA.

Nucleic Acid Conformation↗

PubMed2004

Symmetric K+ and Mg2+ ion-binding sites in the 5S rRNA loop E inferred from molecular dynamics simulations.

Potassium binding to the 5S rRNA loop E motif has been studied by molecular dynamics at high (1.0 M) and low (0.2 M) concentration of added KCl in the presence and absence of Mg2+. A clear pattern of seven deep groove K+ binding sites or regions, in all cases connected with guanine N7/O6 atoms belonging to GpG, GpA, and GpU steps, was identified, indicating that the LE deep groove is significantly more ionophilic than the equivalent groove of regular RNA duplexes. Among all, two symmetry-related sites (with respect to the central G.A pair) were found to accommodate K+ ions with particularly long residence times. In a preceding molecular dynamics study by Auffinger et al. in the year 2003, these two sites were described as constituting important Mg2+ binding locations. Altogether, the data suggest that these symmetric sites correspond to the loop E main ion binding regions. Indeed, they are located in the deep groove of an important ribosomal protein binding motif associated with a fragile pattern of non-Watson-Crick pairs that has certainly to be stabilized by specific Mg2+ ions in order to be efficiently recognized by the protein. Besides, the other sites accommodate monovalent ions in a more diffuse way pointing out their lesser significance for the structure and function of this motif. Ion binding to the shallow groove and backbone atoms was generally found to be of minor importance since, at the low concentration, no well defined binding site could be characterized while high K+ concentration promoted mostly unspecific potassium binding to the RNA backbone. In addition, several K+ binding sites were located in positions equivalent to water molecules from the first hydration shell of divalent ions in simulations performed with magnesium, indicating that ion binding regions are able to accommodate both mono- and divalent ionic species. Overall, the simulations provide a more precise but, at the same time, a more intricate view of the relations of this motif with its ionic surrounding.

Binding Sites↗

PubMed2004

Anion binding to nucleic acids.

Nucleic acids are generally considered as efficient cation binders. Therefore, the likelihood that negatively charged ions might intrude their first hydration shell is rarely considered. Here, we show on the basis of (i) a survey of the Nucleic Acid Database, (ii) several structures extracted from the Cambridge Structural Database, and (iii) molecular dynamics simulations, that the nucleotide electropositive edges involving mainly amino, imino, and hydroxyl groups can cast specific anion binding sites. These binding sites constitute also good locations for the binding of the negatively charged groups of the Asp and Glu residues or the nucleic acid phosphate groups. Furthermore, it is observed in several instances that anions, like water molecules and cations, do mediate protein/nucleic acid interactions. Thus, anions as well as negatively charged groups are directly involved in specific recognition and folding phenomena involving polyanionic nucleic acids.

Anions↗

PubMed2003

The apical loop of the HIV-1 TAR RNA hairpin is stabilized by a cross-loop base pair.

The TAR hairpin of the HIV-1 RNA genome is indispensable for trans-activation of the viral promoter and virus replication. The TAR structure has been studied extensively, but most attention has been directed at the three-nucleotide bulge that constitutes the binding site of the viral Tat protein. In contrast, the conformational properties of the apical loop have remained elusive. We performed biochemical studies and molecular dynamics simulations, which indicate that the TAR loop is structured and stabilized by a cross-loop base pair between residues C30 and G34. Mutational disruption of the cross-loop base pair results in reduced Tat response of the LTR promoter, which can be rescued by compensatory mutations that restore the base pair. Thus, Tat-mediated transcriptional activation depends on the structure of the TAR apical loop. The C30-G34 cross-loop base pair classes TAR in a growing family of hairpins with a structured loop that was recently identified in ribosomal RNA, tRNA, and several viral and cellular mRNAs.

2-Aminopurine↗

PubMed2003

The Mg2+ binding sites of the 5S rRNA loop E motif as investigated by molecular dynamics simulations.

Molecular dynamics simulations have been used to investigate the binding of Mg(2+) ions to the deep groove of the eubacterial 5S rRNA loop E. The simulations suggest that long-lived and specific water-mediated interactions established between the hydrated ions and the RNA atoms lining up the binding sites contribute to the stabilization of this motif. The Mg(2+) binding specificity is modulated by two factors: (i) a required electrostatic complementarity and (ii) a structural correspondence between the hydrated ion and its binding pocket that can be estimated by its degree of dehydration and the resulting number and lifetime of the intervening water-mediated contacts. Two distinct binding modes for pentahydrated Mg(2+) ions that result in a significant freezing of the tumbling motions of the ions are described, and mechanistic details related to the stabilization of nucleic acids by divalent ions are provided.

Binding Sites↗

PubMed2002

The bulge region of HIV-1 TAR RNA binds metal ions in solution.

Binding of Mg2+, Ca2+ and Co(NH3)6(3+) ions to the HIV-1 TAR RNA in solution was analysed by 19F NMR spectroscopy, metal ion-induced RNA cleavages and Brownian dynamics (BD) simulations. Chemically synthesised 29mer oligoribonucleotides of the TAR sequence labelled with 5-fluorouridine (FU) were used for 19F NMR-monitored metal ion titration. The chemical shift changes of fluorine resonances FU-23, FU-25 and FU-40 upon titration with Mg2+ and Ca2+ ions indicated specific, although weak, binding at the bulge region with the dissociation constants (K(d)) of 0.9 +/- 0.6 and 2.7 +/- 1.7 mM, respectively. Argininamide, inducing largest (19)F chemical shifts changes at FU-23, was used as a reference ligand (K(d) = 0.3 +/- 0.1 mM). In the Pb2+-induced TAR RNA cleavage experiment, strong and selective cleavage of the C24-U25 phosphodiester bond was observed, while Mg2+ and Ca2+ induced cuts at all 3-nt residues of the bulge. The inhibition of Pb2+-specific TAR cleavage by di- and trivalent metal ions revealed a binding specificity [in the order Co(NH3)6(3+) > Mg2+ > Ca2+] at the bulge site. A BD simulation search of potential magnesium ion sites within the NMR structure of HIV-1 TAR RNA was conducted on a set of 20 conformers (PDB code 1ANR). For most cases, the bulge region was targeted by magnesium cations.

Arginine↗

PubMed2002

The molecular dynamics thermocycler. A new approach to sample conformational space, as exemplified by the RNA hairpin.

The approach called the molecular dynamics thermocycler employs repeated cycles of heating and cooling of the model during the course of unrestrained in aqua MD simulation. It is validated by confronting results of three 1.6 ns simulations using different heating temperatures, starting from a de novo constructed 12-mer RNA hairpin model containing a UGAA loop vs. the set of NMR derived coordinates (PDB code 1AFX). The lowest average RMS deviation and best coherence with the experimentally delivered structures was identified in case of the molecular dynamics thermocycler using Tmax = 400 K.

Nuclear Magnetic Resonance, Biomolecular↗