抄録
In nature, curdlan and other β-1,3-D-glucan adopt a right-handed 61 triple helix, which is underpinned by the intermolecular hydrogen bonds between the constituent glucoses. Curdlan forms a stoichiometric complex with polynucleotides (e.g., poly (cytidylic acid): poly(C)). We carried out a semi-empirical quantum-mechanics calculation (MOPAC) to speculate a molecular structure for the curdlan/poly(C) complex. The calculation exhibited that two types of hydrogen bonds are formed between the 2nd OH of the curdlan main chain and the cytosine of poly(C). In the calculated model, the conformation of the helix is different from that of the single chain. The helix diameter is expanded from 11.0 to 15.3 Å upon complexation. Despite of the conformational change induced upon the complexation, the 61 helix structure of poly(C) in the complex was maintained as the original single chain. This fact agrees with the experimental result that the complexation did not change the circular dichroic spectral shape. The chain length relationship of the reaction enthalpy change indicates that the complexation is more favorable than the decomplexation when the chain of the curdlan/poly(C) complex is long enough.
