1c58

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spinqualitylabelsall models 1c58, resolution 0.99Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

CRYSTAL STRUCTURE OF CYCLOAMYLOSE 26

Overview

The amylose fraction of starch occurs in double-helical A- and B-amyloses, and the single-helical V-amylose. The latter contains a channel-like, central cavity that is able to include molecules, "iodine's blue" being, the best-known representative. Molecular models of these amylose forms, have been deduced by solid state 13C cross-polarization/magic angle, spinning NMR and by x-ray fiber and electron diffraction combined with, computer-aided modeling. They remain uncertain, however, as no structure, at atomic resolution is available. We report here the crystal structure of, a hydrated cycloamylose containing 26 glucose residues, (cyclomaltohexaicosaose, CA26), which has been determined by, real/reciprocal space recycling starting from randomly positioned atoms or, from an oriented diglucose fragment. This structure provides conclusive, evidence for the structure of V-amylose, as the macrocycle of CA26 is, folded into two short left-handed V-amylose helices in antiparallel, arrangement and related by twofold rotational pseudosymmetry. In the, V-helices, all glucose residues are in syn orientation, forming systematic, interglucose O(3)n...O(2)(n+l) and O(6)n...O(2)(n+6)/O(3)(n+6) hydrogen, bonds; the central cavities of the V-helices are filled by disordered, water molecules. The folding of the CA26 macrocycle is characterized by, typical "band-flips" in which diametrically opposed glucose residues are, in anti rather than in the common syn orientation, this conformation being, stabilized by interglucose three-center hydrogen bonds with O(3)n as donor, and O(5)(n+l), O(6)(n+l) as acceptors. The structure of CA26 permitted, construction of an idealized V-amylose helix, and the band-flip motif, explains why V-amylose crystallizes readily and may be packed tightly in, seeds.

About this Structure

1C58 is a Protein complex structure of sequences from [1]. Full crystallographic information is available from OCA.

Reference

V-Amylose at atomic resolution: X-ray structure of a cycloamylose with 26 glucose residues (cyclomaltohexaicosaose)., Gessler K, Uson I, Takaha T, Krauss N, Smith SM, Okada S, Sheldrick GM, Saenger W, Proc Natl Acad Sci U S A. 1999 Apr 13;96(8):4246-51. PMID:10200247

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