Structure and stability of polynucleotide-(1,3)-β-D-glucan complexes

The structure and stability of complexes formed between (1,3)- β-D-glucans and the polynucletide poly(C) are investigated using differential scanning calorimetry (DSC), atomic force microscopy (AFM) and size exclusion chromatography (SEC). DSC revealed the melting transition of the complexes at 55 °C and an endothermic transition for renatured scleroglucan in the interval 30–40 °C. AFM topographs support the interpretations that the latter transition is due to melting of associated polymer sequences positioned in between structural defects in renatured triplexes. The complexes form between poly(C) and single stranded or renatured scleroglucan, but not with annealed scleroglucan. The complex formation thus seems to require single strands, but the short single stranded stretches present in renatured scleroglucan are sufficient, and full dissociation into single strands is not required. No differences were observed between complexes formed by adding poly(C) to renatured triple helical or denatured single stranded (1,3)- β-D-glucans. Implications of this insight on proposed structural models are discussed.