Sialic acid oligomer

However, in the a-(268) linked sialic acid oligomers, the OH-8 is replaced by OR-8, where R is the bulky quaternary center C-2 of the next sialic acid. Not surprisingly, in the a-(268) linked sialic acid trisaccharide and in the a-(268) linked sialic acid polymer, colominic acid, mixtures of rotamers about the C-7-C-8 bond are adopted [219,220] that have been interpreted for the polymer as giving a helix [221] or a short-lived helix [219], consistent with this polymer being a conformational epitope for serogroup B of Neisseria meningitidis. More recent detailed NMR relaxation studies have concluded that the polymer is a random coil with no helix present for any extended period and that the polymer has considerable flexibility about the exocyclic torsional angles [222]. 

The crystal structure of the catalytic part of endoNF (amino acids 246-910) has been solved in three studies [12,106,113] (Table 3). First, the protein structure has been solved in its apo state and with bound substrate after soaking of sialic acid trimer. By this means, two oligosialic acid binding sites have been identified [12] (see Fig. 2c and Sect. 8). To allow identification of longer sialic acid oligomers bound to endoNF, two active site mutants have been created upon structural information from the first structure [106]. Finally, an endoNF structure has been solved at the high resolution of 0.98 A [113]. 

Substrate [A] — DP3 Observed sialic acid oligomer DP3 DP5 DP5t DP3 ... 

Synthesis of an Oligomer of Sialic Acid 5.1 [Pg.1343]

Despite the development of the exquisite methods for a-(2-8)-linked disialic acid synthesis discussed above, the assembly of the a-(2-8)-linked oligomer has been far from a success. Recently, Tanaka disclosed the unpredictable difficulty of the oligomer synthesis. As mentioned above, the coupling of A-Troc-protected sialic acid donor and acceptor successfully delivered the dimer of sialic acid. However, the A-Troc donor 163 was hardly incorporated into the A-Troc disialyl acceptor 164 the glycosylation produced the stereo mixture of trisial-ic acid 165 in 6% yield (O Scheme 45) [114]. 

Horseshoe crab limulin binds to mammalian sialic acids and bacterial KDO [213] and is a sialic acid-specific hemagglutinin as well as cytolytic to erythrocytes in vitro [214]. In contrast to other pentraxins, limulin subunits have been proposed to associate as twelve 45 kDa AB complexes in doubly stacked hexameric disc-like oligomers [202,214]. 

Identification of polysialic acid as posttransladonal modification of NCAM has been based on the release of oligomers of sialic acid from it by incubation with... 

Bergwerfif, A. A., Hulleman, S.H.D., Kamerling, J. P., Vliegenthart, J.F.G., Shaw, L., Reuter, G., and Schauer, R., 1992, Nature and biosynthesis of sialic acids in the starfish Asterias rubens. Identification of sialo-oligomers and detection of S-adenosyl-L-methionine N-acylneuraminate... 

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