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Biomedical subjects

Piet Herdewijn

Publications and source records attributed to Piet Herdewijn.

At least 19 recordsLinked to original sources
PubMed2007

Structure of the alpha-homo-DNA:RNA duplex and the function of twist and slide to catalogue nucleic acid duplexes.

High-resolution NMR studies of an alpha-homo-DNA:RNA duplex reveal the formation of a right-handed parallel-oriented helix. It differs significantly from a standard A- or B-type helix by a small twist value (26.2 degrees ), which leads to a helical pitch of 13.7 base pairs per helical turn, a negative inclination (-1.78 Angstrom) and a large x displacement (5.90 Angstrom). The rise (3.4 Angstrom) is similar to that found in B-DNA. The solution of this new helix structure has stimulated us to develop a mathematical and geometrical model based on slide and twist parameters to describe nucleic acid duplexes. All existing duplexes can be positioned within this landscape, which can be used to understand the helicalization process.

Magnetic Resonance Spectroscopy↗
PubMed2006

Complete NMR characterization of lychnose from Stellaria media (L.) Vill.

Lychnose (alpha-D-Gal-(1-->6)-alpha-D-Glc-(1-->2)-beta-D-Fru-(1-->1)-alpha-D-Gal) was isolated from Stellaria media, a representative member of the Caryophyllaceae plant family. Weak acid hydrolysis, enzymatic hydrolysis and complete NMR characterization were performed to confirm the identity of the tetrasaccharide. All (1)H and (13)C resonances were unambiguously assigned and the conformation of the sugars was determined using one and two dimensional NMR techniques. Anomeric characterizations in lychnose were confirmed from HMBC and NOESY spectra.

Carbohydrate Conformation↗
PubMed2006

Base-base interactions in the minor groove of double-stranded DNA.

A method has been developed for the synthesis of bisheaded nucleosides with thymine and adenine base moieties. We have demonstrated that, when incorporated in oligonucleotides, extrahelical A-T base interactions are possible when the bisheaded nucleosides are positioned in opposite strands of the duplex and are separated from each other by one regular base pair.

Adenine↗
PubMed2006

The naturally occurring N6-threonyl adenine in anticodon loop of Schizosaccharomyces pombe tRNAi causes formation of a unique U-turn motif.

Modified nucleosides play an important role in structure and function of tRNA. We have determined the solution structure of the anticodon stem-loop (ASL) of initiator tRNA of Schizosaccharomyces pombe. The incorporation of N6-threonylcarbamoyladenosine at the position 3' to the anticodon triplet (t6A37) results in the formation of a U-turn motif and enhances stacking interactions within the loop and stem regions (i.e. between A35 and t6A37) by bulging out U36. This conformation was not observed in a crystal structure of tRNAi including the same modification in its anticodon loop, nor in the solution structure of the unmodified ASL. A t6A modification also occurs in the well studied anti-stem-loop of lys-tRNA(UUU). A comparison of this stem-loop with our structure demonstrates different effects of the modification depending on the loop sequence.

Adenine↗
PubMed2006

The interplay between antiviral activity, oligonucleotide hybridisation and nucleic acids incorporation studies.

Nucleoside analogues have been the most successful antiviral compounds. Likewise, they are the most intriguing antiviral compounds, because of their structural relationship to natural nucleosides. This is also the reason why the design process of a potential selective antiviral nucleoside is so difficult. Too many natural processes (from cellular uptake to DNA incorporation) and too many enzymes are involved in their biological effect (activity/toxicity/catabolism/anabolism) to make the design process readily predictable. The relationship between the physicochemical and biochemical properties of nucleoside analogues and their antiviral activity is very complex and could only be understood on a very long term basis. Here we try to explain some of the reasoning that was made during the design process leading to new potent antivirals with a phosphonate functionality.

Anti-HIV Agents↗
PubMed2006

Glycosyl transferase activity of the Escherichia coli penicillin-binding protein 1b: specificity profile for the substrate.

The glycosyl transferase of the Escherichia coli bifunctional penicillin-binding protein (PBP) 1b catalyzes the assembly of lipid-transported N-acetylglucosaminyl-beta-1,4-N-acetylmuramoyl-L-Ala-gamma-D-Glu-meso-A2pm-D-Ala-D-Ala units (lipid II) into linear peptidoglycan chains. These units are linked, at C1 of N-acetylmuramic acid (MurNAc), to a C55 undecaprenyl pyrophosphate. In an in vitro assay, lipid II functions both as a glycosyl donor and as a glycosyl acceptor substrate. Using substrate analogues, it is suggested that the specificity of the enzyme for the glycosyl donor substrate differs from that for the acceptor. The donor substrate requires the presence of both N-acetylglucosamine (GlcNAc) and MurNAc and a reactive group on C1 of the MurNAc and does not absolutely require the lipid chain which can be replaced by uridine. The enzyme appears to prefer an acceptor substrate containing a polyprenyl pyrophosphate on C1 of the MurNAc sugar. The problem of glycan chain elongation that presumably proceeds by the repetitive addition of disaccharide peptide units at their reducing end is discussed.

Carbohydrate Sequence↗
PubMed2006

A novel, highly selective inhibitor of pestivirus replication that targets the viral RNA-dependent RNA polymerase.

We report on the highly potent and selective antipestivirus activity of 5-[(4-bromophenyl)methyl]-2-phenyl-5H-imidazo[4,5-c]pyridine (BPIP). The 50% effective concentration (EC50) for inhibition of bovine viral diarrhea virus (BVDV)-induced cytopathic effect formation was 0.04 +/- 0.01 microM. Comparable reduction of viral RNA synthesis (EC50 = 0.12 +/- 0.02 microM) and production of infectious virus (EC50= 0.074 +/- 0.003 microM) were observed. The selectivity index (ratio of 50% cytostatic concentration/EC50) of BPIP was approximately 2,000. BPIP was inactive against the hepatitis C virus subgenomic replicon and yellow fever virus but demonstrated weak activity against GB virus. Drug-resistant mutants were at least 300-fold less susceptible to BPIP than wild-type virus; showed cross-resistance to N-propyl-N-[2-(2H-1,2,4-triazino[5,6-b]indol-3-ylthio)ethyl]-1-propanamine (VP32947), and carried the F224S mutation in the viral RNA-dependent RNA polymerase (RdRp). When the F224S mutation was introduced into an infectious clone, the drug-resistant phenotype was obtained. BPIP did not inhibit the in vitro activity of recombinant BVDV RdRp, but did inhibit the activity of replication complexes (RCs). Computational docking revealed that F224 is located at the top of the finger domain of the polymerase. Docking of BPIP in the crystal structure of the BVDV RdRp revealed aromatic ring stacking, some hydrophobic contacts, and a hydrogen bond. Since two structurally unrelated compounds, i.e., BPIP and VP32947, target the same region of the BVDV RdRp, this position may be expected to be critical in the functioning of the polymerase or assembly of the RC. The potential of BPIP for the treatment of pestivirus and hepacivirus infections is discussed.

Antiviral Agents↗
PubMed2005

Incorporation of a disaccharide nucleoside into the backbone of double-stranded DNA: crystallization and preliminary X-ray diffraction.

Incorporation of a disaccharide nucleoside into double-stranded DNA can be considered as a chemical (non-enzymatic) alternative for site-specific cleavage of DNA. Crystals of the sequence d(CGCGAATT*CGCG), where * is an incorporated ribose, were obtained by hanging-drop vapour diffusion and diffracted to 2.6 A. The crystals belong to the orthorhombic space group P222(1), with unit-cell parameters a = 41.52, b = 57.63, c = 81.39 A, indicating a new crystal packing motif for an oligonucleotide dodecamer sequence.

Crystallization↗
PubMed2005

Pseudouridine detection improvement by derivatization with methyl vinyl sulfone and capillary HPLC-mass spectrometry.

A method is presented for improved detection of pseudouridine in nucleoside mixtures based on the specific derivatization with methyl vinyl sulfone followed by analysis by capillary HPLC-mass spectrometry. Reaction conditions were optimized in order to obtain the best yield and specificity. The method was successfully applied to different nucleoside mixtures.

Chromatography, High Pressure Liquid↗
PubMed2005

Investigation of the DNA-dependent cyclohexenyl nucleic acid polymerization and the cyclohexenyl nucleic acid-dependent DNA polymerization.

DNA polymerases from different evolutionary families [Vent (exo-) DNA polymerase from the B-family polymerases, Taq DNA polymerase from the A-family polymerases and HIV reverse transcriptase from the reverse transcriptase family] were examined for their ability to incorporate the sugar-modified cyclohexenyl nucleoside triphosphates. All enzymes were able to use the cyclohexenyl nucleotides as a substrate. Using Vent (exo-) DNA polymerase and HIV reverse transcriptase, we were even able to incorporate seven consecutive cyclohexenyl nucleotides. Using a cyclohexenyl nucleic acid (CeNA) template, all enzymes tested were also able to synthesize a short DNA fragment. Since the DNA-dependent CeNA polymerization and the CeNA-dependent DNA polymerization is possible to a limited extend, we suggest CeNA as an ideal candidate to use in directed evolution methods for the development of a polymerase capable of replicating CeNA.

Biopolymers↗
PubMed2005

Synthesis and conformational analysis of a ribo-type cyclohexenyl nucleoside.

A straightforward approach to a novel class of ribo-type cyclohexenyl nucleosides is described. An electron-demand Diels-Alder reaction forms the key-step of the chosen synthetic pathway. Although the difference is small, conformational analysis using NMR shows that this nucleoside analogue adopts preferentially an 2H3 conformation (S-type), while the "deoxy" cyclohexenyl analogue has a preference for a C3' endo conformation (N-type). Analyses of the conformational equilibrium reveal that, in the given experimental conditions, the difference between adenosine and its cyclohexenyl congener resides in their different DeltaG values; furthermore, in adenosine, the conformational preference is of enthalpic origin, whereas in the cyclohexenyl congener, the conformational preference is of entropic origin.

Adenosine↗
PubMed2005

Oligonucleotides with cyclohexene-nucleoside building blocks: crystallization and preliminary X-ray studies of a left-handed sequence GTGTACAC.

Cyclohexene nucleic acids contain a cyclohexene ring instead of the normal beta-D-2'-deoxyribose. The cyclohexene oligonucleotide GTGTACAC was synthesized using phosphoramidite chemistry and standard protecting groups. Crystals of GTGTACAC were obtained at 289 K by the hanging-drop vapour-diffusion technique. The crystals diffract to 1.7 A resolution and belong to the trigonal space group R3, with unit-cell parameters a = 41.434, c = 66.735 A.

Base Sequence↗
PubMed2005

Cyclohexenyl nucleic acids: conformationally flexible oligonucleotides.

Cyclohexenyl nucleic acid (CeNA) is a nucleic acid mimic, where the (deoxy)ribose sugar has been replaced by cyclohexenyl moieties. In order to study the conformation of cyclohexenyl nucleosides by NMR, the HexRot program was developed to calculate conformations from scalar coupling constants of cyclohexenyl compounds, analogous to the methods applied for (deoxy)ribose nucleosides. The conformational equilibria and the values of the thermodynamic parameters are very similar between a cyclohexenyl nucleoside [energy difference between 2H3 (N-type) and 2H3 (S-type) is 1.8 kJ/mol and equilibrium occurs via the eastern hemisphere with a barrier of 10.9 kJ/mol] and a natural ribose nucleoside (energy difference between N-type and S-type is 2 kJ/mol and equilibrium occurs via the eastern hemisphere with a barrier of 4-20 kJ/mol). The flexibility of the cyclohexenyl nucleoside was demonstrated by the fast equilibrium between two conformational states that was observed in a CeNA-U monomer, combined with the 2H3 conformation of the cyclohexene moiety when incorporated into a Dickerson dodecamer and the 2H3 conformation when incorporated in a d(5'-GCGT*GCG-3')/d(5'-CGCACGC-3') duplex, as determined by the NMR spectroscopy. This represents the first example of a synthetic nucleoside that adopts different conformations when incorporated in different double-stranded DNA sequences.

Base Sequence↗
PubMed2005

Deoxythreosyl phosphonate nucleosides as selective anti-HIV agents.

Out of a series of eight new phosphonate nucleosides with an l-threose and an l-2-deoxythreose sugar moiety, two new compounds were identified (PMDTA and PMDTT) that showed potent anti-HIV-1 (HIV-2) activity [EC50 = 2.53 microM (PMDTA) and 6.59 microM (PMDTT)], while no cytoxicity was observed at the highest concentration tested [CC50 > 316 microM (PMDTA) and > 343 microM (PMDTT)]. The kinetics of incorporation of PMDTA into DNA (using the diphosphate of PMDTA as substrate and HIV-1 reverse transcriptase as catalyst) was similar to the kinetics observed for dATP, while the diphosphate of PMDTA was a very poor substrate for DNA polymerase alpha. The incorporated PMDTA fits very well in the active site pocket of HIV-1 reverse transcriptase.

Anti-HIV Agents↗
PubMed2005

Reinforced HNA backbone hydration in the crystal structure of a decameric HNA/RNA hybrid.

The crystal structure of a decameric HNA/RNA (HNA = 2',3'-dideoxy-1',5'-anhydro-d-arabinohexitol nucleic acid) hybrid with the RNA sequence 5'-GGCAUUACGG-3' is the first crystal structure of a hybrid duplex between a naturally occurring nucleic acid and a strand, which is fully modified to contain a six-membered ring instead of ribose. The presence of four duplex helices in the asymmetric unit allows for a detailed discussion of hydration, which revealed a tighter spinelike backbone hydration for the HNA- than for the RNA-strands. The reinforced backbone hydration is suggested to contribute significantly to the exceptional stability of HNA-containing duplexes and might be one of the causes for the evolutionary preference for ribose-derived nucleic acids.

Crystallography, X-Ray↗
PubMed2005

Hexitol nucleic acid-containing aptamers are efficient ligands of HIV-1 TAR RNA.

The transactivation responsive element (TAR) plays a crucial role in the transcription of the HIV-1 genome upon specific binding of the viral protein Tat and cellular proteins. We have previously identified a RNA hairpin aptamer forming a stable and specific kissing complex with TAR RNA (Ducongé, F., and Toulmé, J. J. (1999) RNA 5, 1605-1614). We chemically modified this aptamer with hexitol nucleic acid (HNA) residues. We demonstrate that a fully HNA-modified aptamer is a poor ligand but, in contrast, mixmers containing both HNA and unmodified RNA nucleotides display interesting properties. Two HNA-RNA mixmers bind to TAR with an equilibrium dissociation constant in the low-nanomolar range and show a reduced nuclease sensitivity. In addition, they show a moderate dependence on magnesium ions for binding to TAR. These HNA-RNA mixmers are able to inhibit transactivation of transcription in an in vitro assay.

Base Sequence↗
PubMed2005

Synthesis and properties of aminopropyl nucleic acids.

Oligonucleotides that contain up to three aminopropyl nucleoside analogues have been synthesized. Dimers of aminopropyl adenine and thymidine were prepared and used as building blocks by applying phosphoramidite chemistry. Both R and S isomers of the aminopropyl nucleosides were used. This incorporation led to a reduction of thermal stability of double-stranded DNA. Furthermore, the (R)-adenine analogue, which yielded (S)-APNA, can be considered as a candidate for universal base pairing.

Adenine↗