Structure and chain conformation of a neutral intracellular heteropolysaccharide from mycelium of Paecilomyces cicadae

A neutral heteropolysaccharide (PCIPS2) was isolated and purified from mycelium of Paecilomyces cicadae, which was investigated to be mainly composed of d-mannose, l-rhamnose, 3-O-methyl-d-galactose, d-glucose and d-galactose with a molar ratio of 47.9:3.1:6.4:0.9:0.8. It had a backbone of 1,4-linked α-l-Rhap residues and 1,6-linked α-d-Manp residues with branches at O-3 of α-d-Manp residues. Its side chain was comprised of minor terminal β-d-glucose and 1,4-linked α-3-O-Me-d-Galp residues terminated by α-d-galactose. Furthermore, its chain information on the values of weight-average molar mass (Mw), root mean square radius (〈S2〉z1/2), hydrodynamic radius (Rh) and intrinsic viscosity ([η]) for PCIPS2 were analyzed to be 3.09 × 104 g/mol, 7.8 nm, 3.6 nm and 8.5 mL/g, respectively. The structural exponent α of 0.57 indicated that PCIPS2 existed as a flexible chain conformation with a coil-like structure in 0.1 M NaNO3 at 25 °C. In terms of known theory for worm-like chains, the model parameters for PCIPS2 were as following: molar mass per unit contour length (ML) = 379 nm−1, persistence length (q) = 0.74 nm and hydrodynamic diameter of cylinder (d) = 0.82 nm, which were further evidenced by atomic force microscopy (AFM).