Molecular structures for microbial polysaccharides: x-ray diffraction results from Klebsiella serotype K57 capsular polysaccharide |
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Authors: | David H. Isaac Kenn H. Gardner Edward D.T. Atkin Ursula Elsasser-Beile Stephan Stirm |
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Affiliation: | University of Bristol, H. H. Wills Physics Laboratory, Bristol B58 1TL Great Britain;Max-Planck-Institute für Immunbiologie, 78 Freiburg-Zahringen, Postfach 1169 G.F.R. |
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Abstract: | Fibre X-ray diffraction patterns have been obtained from oriented, semi-crystalline films of the Klebsiella capsular polysaccharide secrotype K57. K57 is a polytetrasaccharide that contains galactosyluronic acid, mannosyl, and galactosyl residues in the backbone, and an additional mannosyl group as a side-appendage. The simplest interpretation of the diffraction pattern is that the molecule crystallizes as a three-fold helix with an axially projected repeat of 1.143 nm which correlates directly with the chemical repeat. The chain is highly extended, even though it incorporates a 1,2-diaxial linkage in the main backbone. Molecular models have been built using least-squares techniques to minimise interatomic compression and simultaneously meet the observed helical parameters. These models have been compared with the experimental data by using cylindrically averaged, Fouriertransform calculations. |
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