Glucan crystal structure

Cook WJ, Bugg CE (1973) Calcium interactions with D-glucans crystal structure of o,a-trehalose-calcium bromide monohydrate. Carbohydr Res 31 265-275. doi 10.1016/S0008-6215(00)86191-1... 

The change of the crystal structure of (l- -3)-a-D-glucan should be compared to the case of (l- -3)-3-D-glucan (curdlan). Although curdlan changes its polymorphic form by annealing (6), neither the fiber patterns (samples B and C) nor the powder patterns (samples A and D) underwent polymorphic transformations due to annealing. 

As the X-ray diffraction diagrams of an oriented gel (Fig. 6) are poorly crystalline, it has been useful to conduct X-ray crystal structure analyses of oligomer of 3-(l->-3)-D-glucan. The molecular structures of laminarabiose and its acetyl derivative have been determined. 

Without doubt, concanavalin A (Con A) is the most celebrated and has proven to be one of the most useful of the plant lectins. Its physical chemical properties and carbohydratebinding properties are well documented in previous reviews [3,8]. Suffice it to note that it was first isolated and crystallized by Sumner and Howell in 1936, who showed it to require metal ions for its activity [74]. By virtue of its interaction with branched a-D-glucans, it is readily prepared by affinity chromatography on crossed-linked dextran (Sephadex) [75, 76]. A homotetramer at pH 7 (subunit M, = 26 500 Da) of Con A has been sequenced [77] and its crystal structure determined both in its native form [38,39] and complexed with methyl a-D-mannopyranoside [40] and Man(al-3)[Man(al-6)]Man[49]. 

Crystal Structure. Curdlan powder was the source of (l->- 3)- 6 -D-glucan uTed in our study since it is commercially available and has been demonstrated to be a linear chain constituted almost exclusively of (l->3)-3-D-glucose residues. The polysaccharide was obtaineci from Takeda Chemicals Company in Japan and its morphology has been previously described.(, 1J ) It is received as a spray-dried powder which is very poorly crystalline. 

The alpha-1,3-glucans arise from fungi and other primitive plants. A number of different crystalline forms, or allomorphs, have been reported (2.> ) every case of which this writer is aware, the shape of crystalline alpha-l,3-glucan is a fully extended 2-fold helix. The differences in crystal structure arise from different packings of similar chains and depend on the history and the amount of water in the structure. From the n-h map (Figure 3), it is easy to see why only one shape is found. The extended conformation is isolated from all other conformations on the n-h map. 

The process of the artificial cellulose was visually analyzed by using transmission electron microscopy (24). Cellulose formation was detected as early as 30 s after the initial stage of the reaction in the aqueous acetonitrile. The electron diffraction pattern of the product showed the typical pattern of the crystal structure of thermodsmamically stable cellulose II with antiparallel orientation between each glucan chains. When the purified cellulase (39 kDa) was used, cellulose microfibrils with an electron diffraction pattern characteristic of metastable cellulose I with parallel orientation, an allomorph of natural cellulose, were first observed in an artificial process (25). Based on these results, a new concept of choroselectivity, selectivity concerning the relative ordering of the polymer chain direction, in polsrmerization chemistry has been proposed (26-28). 

The crystal structures of two polymorphic forms of pachyman acetate, the fully acetylated derivative of a naturally-occurring (1 3)-j3-D-glucan, have been determined by a combination of stereochemical and A -ray diffraction analyses. ... 

Single crystals of the D-glucan from Acetobacter xijlinum were prepared in water-methanol solutions at room temperature. Using electron and X-ray diffraction, a hexagonal unit-cell, with a = h = 0.518 nm and c = 2.0 nm, was derived. It was concluded that the chain axes lie parallel to the surface of the lamellar crystals, that there are 2.5 water molecules per /3-D-Glcp residue, and that the structure is similar to that of cellulose hydrate II (Ref. 42). 

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