Strontium and DNA Aptamer Folding
In addition to classical double-stranded helical structure, some DNA sequences can form some unusual structures. Such unusual nucleic acid structures are illustrated by aptamers that consist of short synthetic DNA or RNA sequences that adapt well-defined three-dimensional structures and bind to specific biomolecules. For example, the 15-mer oligonucleotide with a d(G2T2G2TGTG2T2G2) sequence is one of the thrombin-binding aptamers (TBA) that binds to the serine protease thrombin with high affinity and inhibits the thrombin-catalyzed fibrin-clot formation. The unique spatial structure of TBA, the intramolecular G-quadruplex, is stabilized by the specific coordination of metal ions. Although various cations can stabilize aptamers, the highest stability was ascribed to Sr2+-aptamers.