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1. (Article ID: 530)
 
Ridout M, Cairns P, Brownsey G, Morris V
Synergistic interactions between the genetically modified bacterial polysaccharide P2 and carob or konjac mannan
Carbohydrate Research 339(13) (2004) 2233-2239
 

Rheological studies have confirmed that the bacterial polysaccharide P2, a genetically modified variant of the Acetobacter xylinum polysaccharide acetan, undergoes synergistic gelation with either of the plant polysaccharides carob or konjac mannan. X-ray fibre diffraction data shows that P2 can form a 5-fold helical structure of pitch 4.7nm and an axial rise per disaccharide repeat of 0.92nm. Optical rotation data demonstrate that P2 undergoes a coil-helix transition in solution and that deacylation enhances the stability of the helical structure in solution. Studies made on mixtures prepared at different temperatures and ionic strengths suggest that denaturation of the P2 helix favours interaction and gelation. Deacetylation of P2 enhances gelation. X-ray diffraction data for oriented fibres prepared from deacetylated P2-konjac mannan mixed films reveal a 6-fold helical structure of pitch 5.54nm with an axial rise per disaccharide repeat also of 0.92nm. This mixed helix provides direct evidence for binding between the two polysaccharides. P2 contains two sites of acetylation: one on the backbone and one on the sidechain. The former site of acetylation inhibits helix formation for P2. It is suggested that this site of acetylation also inhibits formation of the mixed helix, explaining the enhanced gelation of mixtures on deacetylation.

Bacterial polysaccharide, Rheology, Konjac mannan, Mixtures, Carob

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2. (Article ID: 776)
 
Colquhoun IJ, Jay AJ, Eagles J, Morris VJ, Edwards KJ, Griffin AM, Gasson MJ
Structure and conformation of a novel genetically engineered polysaccharide P2
Carbohydrate Research 330(3) (2001) 325-333
 

A new exocellular polysaccharide (P2) has been produced by the manipulation of a glycosyl transferase gene (aceP) involved in the biosynthesis of the polysaccharide acetan by the bacterium Acetobacter xylinum strain CKE5. The P2 polysaccharide has been studied by methylation analysis, reductive cleavage, and 1H and 13C NMR spectroscopy. The data are consistent with the structure predicted when the aceP gene is deactivated: [Molecular structure: see text]. The effect of cooling on proton NMR line width indicates a coil-helix transition in P2 at about 70 degrees C.

NMR, conformation, structure, polysaccharide, methylation, Acetobacter xylinum, AceP gene

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