Polysaccharide–polynucleotide complexes. Part 12. Enhanced affinity for various polynucleotide chains by site-specific chemical modification of schizophyllan

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Abstract
Recently, we found that schizophyllan (SPG), which is a natural and neutral polysaccharide, can form macromolecular complexes with certain polynucleotides. In order to increase the stability and the affinity of the complexes, we synthesized a 2-aminoethanol-appended SPG (N-s-SPG) by utilizing periodate oxidation and reductive amination. Although the modification level was only 2.4 ± 0.3%, the melting temperature of the poly(C)–N-s-SPG complex was increased by 8 °C comparing with the poly(C)–s-SPG complex. In addition, the conformation of the complex was scarcely perturbed by the introduction of amino groups. When we formed complexes of N-s-SPG and other polynucleotides, the melting temperature of their complexes increased without exception. Moreover, the amino modification induced complexation with poly(U), which does not form a complex with SPG. The affinity for the short chain nucleotide was also enhanced. These results indicate that the present modification method is quite useful to improve complex stability and we believe, therefore, that this strategy will make it possible to apply SPG to a novel gene carrier.