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1c58

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[[Image:1c58.gif|left|200px]]
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{{Seed}}
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{{STRUCTURE_1c58| PDB=1c58 | SCENE= }}
{{STRUCTURE_1c58| PDB=1c58 | SCENE= }}
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'''CRYSTAL STRUCTURE OF CYCLOAMYLOSE 26'''
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===CRYSTAL STRUCTURE OF CYCLOAMYLOSE 26===
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==Overview==
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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.
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The line below this paragraph, {{ABSTRACT_PUBMED_10200247}}, adds the Publication Abstract to the page
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(as it appears on PubMed at http://www.pubmed.gov), where 10200247 is the PubMed ID number.
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{{ABSTRACT_PUBMED_10200247}}
==About this Structure==
==About this Structure==
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[[Category: Saenger, W.]]
[[Category: Saenger, W.]]
[[Category: Cycloamylose]]
[[Category: Cycloamylose]]
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 12:20:41 2008''
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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jun 30 20:13:46 2008''

Revision as of 17:13, 30 June 2008

Image:1c58.png

Template:STRUCTURE 1c58

CRYSTAL STRUCTURE OF CYCLOAMYLOSE 26

Template:ABSTRACT PUBMED 10200247

About this Structure

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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