Vicky Gheerardijn

Identification of a pKa-regulating motif stabilizing imidazole-modified double-stranded DNA

The predictable 3D structure of double-stranded DNA renders it ideally suited as a template for the bottom-up design of functionalized nucleic acid-based active sites. We here explore the use of a 14mer DNA duplex as a scaffold for the precise and predictable positioning of catalytic functionalities. Given the ubiquitous participation of the histidine-based imidazole group in protein recognition and catalysis events, single histidine-like modified duplexes were investigated. Tethering histamine to the C5 of the thymine base via an amide bond, allows the flexible positioning of the imidazole function in the major groove. The mutual interactions between the imidazole and the duplex and its influence on the imidazolium pKaH are investigated by placing a single modified thymine at four different positions in the center of the 14mer double helix. Using NMR and unrestrained molecular dynamics, a structural motif involving the formation of a hydrogen bond between the imidazole and the Hoogsteen side of the guanine bases of two neighboring GC base pairs is established. The motif contributes to a stabilization against thermal melting of 6°C and is key in modulating the pKaH of the imidazolium group. The general features, prerequisites and generic character of the new pKaH-regulating motif are described.

Surprising duplex stabilisation upon mismatch introduction within triply modified duplexes

Three different modified phosphoramidite nucleoside building blocks equipped with additional protected imidazole, masked alcohol and masked carboxylate functionality are synthesized and incorporated into oligonucleotides. Based on the serine-protease active site model, doubly and triply modified duplexes are created and tested for stability. Analysis of different spatial distributions of the extra functionalities shows that careful positioning can even overcome duplex destabilisation caused by the introduction of mismatches.

Versatile synthesis of amino acid functionalized nucleosides via a domino carboxamidation reaction

Summary Functionalized oligonucleotides have recently gained increased attention for incorporation in modified nucleic acid structures both for the design of aptamers with enhanced binding properties as well as the construction of catalytic DNA and RNA. As a shortcut alternative to the incorporation of multiple modified residues, each bearing one extra functional group, we present here a straightforward method for direct linking of functionalized amino acids to the nucleoside base, thus equipping the nucleoside with two extra functionalities at once. As a proof of principle, we have introduced three amino acids with functional groups frequently used as key-intermediates in DNA- and RNAzymes via an efficient and straightforward domino carboxamidation reaction.

XVIth Symposium on Chemistry of Nucleic Acid Components

SCNAC, the XVIth Symposium on Chemistry of Nucleic Acid Components, was held in Český Krumlov (Czech Republic) in June. This years symposium, which covered the chemistry, biochemistry, biophysics and chemical biology of nucleobases, nucleosides, nucleotides and nucleic acids attracted more than 150 participants from 21 countries to its lectures, oral communications and poster presentations.