Macromolecular cyclization of (1 → 6)‐branched‐(1 → 3)‐β‐D‐glucans observed after denaturation–renaturation of the triple‐helical structure

Abstract

High molecular weight polysaccharide structure is conventionally described in terms of linear, comb-like, or treelike molecules. At a higher level of organization, various single-and multiple-stranded helical geometries have been described in addition to the less well-defined structures and connectivities that occur in noncovalently cross-linked gels. We report here on the finding of circular morphology in one type of high molecular weight multistranded polysaccharide. Circular structures have been described for synthetic polymers and DNA,' but except for the oligomeric cyclodextrins' and cyclosophoraoses,3 circular morphology of high molecular weight polysaccharides has not been reported previously.Samples of schizophyllan,' which dissolve as rigid, triple-helical structures in aqueous solution and random coils in dimethylsulfoxide (DMSO) ,' were subjected to renaturating conditions by dialysis against distilled water of the DMSO solutions. Electron microscopic (EM) observations of heavy metal replicated, vacuum dried specimen^^,^ obtained from the powdered polysaccharide dissolved in aqueous solution revealed almost exclusively linear structures. The limited resolution imposed by the used preparation technique does not allow observations of the side chains in the comb-like schizophyllan structure. Dissolution in DMSO with renaturation by dialysis to aqueous solution at high polymer concentration, i.e., c > 4 mg/mL, yielded predominantly aggregated structures, whereas mixtures of circular, linear, and aggregated structures were observed as a result of lowering the polymer concentration to about 1 mg/mL or below during the dialysis procedure. Circular structures were also observed in samples of lentinan. This is a polysaccharide with a chemical structure similar to that of schizophyllan which has received recent attention for its biological activity and which is currently used as a chemostatic agent in cancer therapy.8Schizophyllan dissolved in mixtures of water and DMSO is reported to undergo two transition^.^ The lowtemperature transition, occurring in pure water near 5"C, is reversible (Figure 1 ) , whereas the triple-helix to random Replicas for EM were prepared as described6 from schizophyllan solutions subjected to different temperature-solvent composition histories. The sample dissolved at W H = 1 is referred to as the starting material; the renaturated sample refers to a sample initially dissolved at w H = 0.0 and subsequently dialyzed against 7 X 1000 mL distilled water at 25°C for 96 h (Figure 1, dashed line). Aliquots of the renatured sample were subsequently heated to 115°C and kept for 2 h (flushed with N2 prior to heating) in a pressurized chamber before being slowly cooled to 25°C. The latter sample is referred to as annealed. Thus, the renatured sample is first carried through the allegedly irreversible random-coil to triple-helix transition and subsequently through the reversible transition. The annealing procedure was selected to enter the onset, but not go through, the triple-helix to random c...

Supramolecular Structure and Renaturation of a (1→3)-β-d-Glucan Compared with Curdlan and Scleroglucan

“…Similar behavior was observed for scleroglucan [4] and schizophyllan [30]. However, it should be mentioned that, for the (1→3)(1→2)-β-D-Glucan, a great dispersion structure sizes was observed (scales are shown below each image), small linear and circular structures ( Figure 4a) coexisted with strands of 5 μm of length (Figure 4b) and small circular structures (Figure 4a) with rod-like linear strands (Figure 4c).…”

Rheological characterization of schizophyllan aqueous solutions after denaturation–renaturation treatment

“…Sato et al 36 and Yanaki et al 22 reported that the renaturation of denatured SPG chains involves two different molecular processes consisting of the collapse of random coil chains to more compact conformation by intrachain hydrogen bonding and the formation of aggregates by interchain hydrogen bonding. Additionally, Stokke et al, 30,31 McIntire et al, 13,32 and Kitamura et al 33 found that the DR treatment results in various DRSPG structures including globular, linear, and circular forms as well as more complicated multichain clusters. In the case of renaturation of partially denatured SPG aqueous solutions, an extended three-dimensional network is developed due to the imperfect registration between the chains forming triple helices.…”

“…13,30 -34 By means of atomic force microscopy, electron microscopy, and gel permeation chromatography, Stokke et al, 30,31 McIntire et al, 13,32 and Kitamura et al 33 found that after DR treatment SPG exists in various forms such as globular, linear, and circular structures as well as more complicated multichain clusters. Vuppu et al 34 reported that the renaturation of partially denatured SPG chains leads to an extended network.…”

Molecular Weight Control of Curdlan (β-1,3-Glucan Polysaccharide) Provides Unique Polynucleotide Binding Properties

“…8,9 Our experiments have established that when the renaturation process is carried out in the presence of certain polynucleotides, the process creates a novel triple helix (the complex formation is schematically shown in Figure 2). In addition, it was also clarified that such complexation can occur commonly in water-soluble -1,3-glucan polysaccharides such as lentinan and laminaran.…”