Klebsiella conformations

The sodium salt form of the Klebsiella K5 polysaccharide crystallizes in a 2(1.35) helical conformation. The intrachain hydrogen-bonds are (i) OH-3-(GlcpA)—0-5-(Manp), (ii) OH-3-(Glcp)—0-5-(GlcpA), and (Hi) OH-2-(Manp)—0-2-(Glcp). 

The conformation of the backbone of the Klebsiella polysaccharide K23[-(l-3)-a-L-Rha-(l-3)-p-D-Glc-]n has been calculated using a force field which includes terms for non bonded interactions, the exo anomeric effect, and hydrogen bonds [203]. The calculated data were checked using NMR spectroscopy. The P-D-Glc-(l-3)-ot-L-Rha bond shows dihedral angles

[Pg.194]

Fig. 27 a, b. Tetrasaccharide with two repeating disaccharide units from Klebsiella capsular polysaccharide K23 in its two energetically favored conformations... 

One further point of interest concerning Klebsiella K5 is that the 0-acetyl groups appear to have little effect on the helix stability. X-ray diffraction patterns taken of de-acetylated material showed that the pitch and type of helix were both identical to those for the acetylated material and further, model building of a deacetylated chain gave rise to the same backbone conformation and system of hydrogen bonds (10). 

Figure 10. Computer-generated projections of a left-handed three-fold helical conformation for Klebsiella K16...

The final Klebsiella polysaccharide that will be mentioned specifically is KZS, whose chemical structure was determined by Niemann et al (24) (Figure 30). This polysaccharide is of particular interesT because its backbone consists of a similar alternating 1, 3 diequatorial, 1, 4 diequatorial glycosidic linkage geometry to that found in the connective tissue polysaccharides, hyaluronic acid, chondroitin sulphate and dermatan sulphate (25). All these three polysaccharides have exhibited 3-fold helical conformations with axially projected chemical repeats in the range 0.95 - 0.97 nm which is comparable to 0.97 nm found in K25 which also forms a 3-fold helix (14). Further, left-handed helices were found to be more favourable in K25 as has previously been observed in the connective tissue polysaccharides. The similarities between these various different structures is apparent in Figure 31 which shows projections down the axis of K25 and several of the connective tissue polysaccharides. 

Figure 29. An enlargement of part of the conformation of Klebsiella K9 shown in Figure 28 showing the orientation of the 1, 2-linked rhamnose residue with respect to the helix axis...

Figure 31. Computer-generated projections down the helix axis of the three-fold left-handed helical conformations of Klebsiella K25, Hyaluronic acid, HA, Chon-droitin 4-sulphate, C4-S, and Chondroitin 6-sulphate, C6-S...

Conforms (E. coli, Klebsiella Gentamicin (or amikacin) Fluoroquinolone third-... 

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