Nanostructured dna-protein aggregates consisting of covalent oligonucleotide-streptavidin conjugates.

Covalent conjugates consisting of streptavidin and a 24-mer single-stranded DNA oligonucleotide have been oligomerized by cross-linking with a 5',5'-bis-biotinylated 169-base-pair double-stranded DNA (dsDNA) fragment. The oligomeric conjugates formed have been analyzed by nondenaturing gel electrophoresis and scanning-force microscopy (SFM). The comparison of analogous oligomers, prepared from native STV and the bis-biotinylated dsDNA fragment, revealed that the covalent STV-oligonucleotide hybrid conjugates self-assemble to generate oligomeric aggregates of significant smaller size, containing on average only about 2.5 times less dsDNA fragments per aggregate. Likely, this is a consequence of electrostatic or steric repulsion between the dsDNA and the single-stranded oligomer covalently attached to the hybrid, as indicated from control experiments. Nevertheless, the single-stranded oligonucleotide moiety within the oligomeric conjugates can be used as a selective molecular handle for further functionalization and manipulation. For instance, it was used for specific DNA-directed immobilization at a surface, previously functionalized with complementary capture oligonucleotides. Moreover, we demonstrate that macromolecules, such as STV and antibody molecules, which are tagged with the complementary oligonucleotide, specifically bind to the supramolecular DNA-STV oligomeric conjugates. This leads to a novel class of functional DNA-protein conjugates, suitable, for instance, as reagents in immuno-PCR or as building blocks in molecular nanotechnology.