Structural examination of polysaccharide/nucleic acid complex by computational chemistry

The β-1,3-D-glucan family is a very abundant cell wall polysaccharide in fungal species. This polysaccharide forms a triple helical structure stabilized by hydrogen bonds. Recently, it was found that β-1,3-D-glucan can form a stoichiometric complex with polynucleotides. In this research, we carried out the MOPAC (semi-empirical molecular-orbital package) calculation to examine the molecular structure of this complex. Our calculation results indicated that the 3′ end of nucleic acid chain orients in the same direction to the reducing ends of the β-1,3-D-glucan chains, and that chain deforms in a large extent upon the complexation. In contrast, the change of β-1,3-D-glucan double strands due to the complexation was small. This complex was stabilized by hydrogen bonds between the 2nd hydroxyl groups of β-1,3-D-glucan and the hydrogen bonding sites of the bases of the nucleic acid chain.