1C58

CRYSTAL STRUCTURE OF CYCLOAMYLOSE 26

Summary for 1C58

• Entry DOI: 10.2210/pdb1c58/pdb
• Descriptor: Cyclohexacosakis-(1-4)-(alpha-D-glucopyranose) (2 entities in total)
• Functional Keywords: cycloamylose, carbohydrate
• Total formula weight: 8467.35

Authors

Gessler, K.,Saenger, W.,Nimz, O. (deposition date: 1999-11-04, release date: 1999-11-10, Last modification date: 2024-04-03)

Primary citation

Gessler, K.,Uson, I.,Takaha, T.,Krauss, N.,Smith, S.M.,Okada, S.,Sheldrick, G.M.,Saenger, W.
V-Amylose at atomic resolution: X-ray structure of a cycloamylose with 26 glucose residues (cyclomaltohexaicosaose).
Proc.Natl.Acad.Sci.USA, 96:4246-4251, 1999

PubMed Abstract: 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.

PubMed: 10200247
DOI: 10.1073/pnas.96.8.4246

Experimental method

X-RAY DIFFRACTION (0.99 Å)