Sialyltransferases tables

Table I. The Effect of Various Compounds Implicated in the 2-Stage Theory of Carcinogenesis on CMP-NeuAc lactosylceramide Sialyltransferase Activity in Human Epithelial Carcinoma with (KB) Cells...

Table III. Comparison of Serum-induced ODC Activity with CMP-NeuAc lactosylceramide Sialyltransferase Activity in Various Cell Lines...

Compound 34 is a triantennary, sialo glycopeptide terminated with NeuAc a-(2- 6)-linked to Gal in all three branches it could be obtained by exhaustive, in vitro sialylation of compound 9 with /3-D-ga-lactoside a-(2— 6)-sialyltransferase.13,78 The Gln-Asn analog of compound 34, in admixture with compound 53 and a glycopeptide analog of 41, has been isolated from human-plasma ceruloplasmin (see compound 53). The 500-MHz, -n.m.r. spectrum of 34 is given in Fig. 26, and its pertinent spectral parameters are listed in Table X. 

The first structure determined for a sialyltransferase (Cstll from Campylobacter jejuni of family GT42 see O Fig. 8c) revealed an unusual variant of the GT-A fold [350]. The protein displays a similar t) e of fold as the canonical GT-A fold, but with some differences in the connectivity of /3-strands (parallel /3-sheet of topology 8712456) and it has no DxD motif. Therefore the Cstll structure represents a new type of fold. Another prokaryotic sialyltransferase has, though, a GT-B fold (see O Table 2). 

Table 10 A Limited Number of CMP-Sialic Acid Derivatives Are Accepted as Substrates by a2,3- and a2,6-Sialyltransferases from Bovine and Human Liver...

So far, the acceptor specificity of nearly 20 eu- and prokaryotic sialyltransferases has been elucidated and 15 different cDNA clones of these enzymes have been obtained (Table 14 and references therein). This list demonstrates the rapid progress in this field and also includes the first cloning of mammalian polysialyltransferase (polysialyltransferase-1 from hamster ovary cells) [620]. The same group has recently published the molecular analysis of the biosynthetic pathway of the a-2,8-polysialic acid capsule by Neisseria meningitidis serogroup B [658]. 

The transfer reaction catalyzed by rat hver a(2 — 6) sialyltransferase using 13 and A-acetyllactosamine as the substrates displayed kinetically significant substrate binding. Even after the observed KIEs for 13 were corrected, they were still too low for any mechanism involving only chemical steps, suggesting that a nonchemical step was kinetically signihcant (Table 5). 

Four of the six different a2,3-sialyltransferases that catalyze the transfer of sialic acid residues in a2,3-linkage onto the terminal Galp residue are involved in mucin glycan chains biosynthesis (Table 3). 

Table 3 Human sialyltransferases, fucosyltransferases and sulfotransferases involved in O-glycan biosynthesis. Sialyltransferase nomenclature is according toTsuji etai, 1996. ...

The requirements for the rat and pork liver sialyltransferases are shown in Table VI. The need for exogenous acceptor is almost absolute and neuraminidase-treated i-acid glycoprotein is far more eflFective than other derivatives, indicating that a terminal galactose residue is required for acceptor activity. The sialyltransferases show no requirements for cations, and the pH optima are 5.7 and 7.0 for the rat and pork liver enzymes, respectively. The Km values for the pork liver enzyme are 0.19 mM for the nucleotide sugar and 0.9 mM for the glycoprotein acceptor (calculated on the basis of available acceptor sites). 

Table V shows that pork liver sialyltransferase will catalyze the transfer of sialic acid to galactosyl-( 8, l->4)-lV-acetylglucosaminyl-R, where R may represent a hydrogen atom or a complex macromolecule such as fetuin or ai-acid glycoprotein. Competition studies (Hudgin and Schachter, 1971a) have shown that the same enzyme or enzymes in pork liver...

The total synthesis of sialosides by using the chemoenzymatic approach is as follows [74]. Sialic acid itself can be synthesized from ManNAc, mannose, or their derivatives by sialic acid aldolase enzyme through aldol condensation reaction. If ManNAc is chemically or enzymatically modified at C2, C4—C6 positions, sialic acid has structural modifications at C5, C7-C9 positions, respectively. The sialic acids are subsequently activated by a CMP-siahc acid synthetase to form a CMP-sialic acid, which is the donor used by sialyltransferases. Because CMP-sialic acid is tmstable, the CMP-Neu5Ac synthetase is valuable for the preparative enzymatic synthesis of sialosides. In the last steps, the CMP-sialic acid is transferred to galactose or GalNAc terminated glycosides by sialyltransferases to form structurally defined sialosides. Examples are that Chen and co-workers have recently developed a one-pot multienzyme system for the efficient synthesis of a-sialosides (Table 2) [12,76,79]. In this system, recombinant E. coli K-12 sialic acid aldolase catalyzed the synthesis of sialic acid precursors for... 

Table 2. The specificity and efficiency of some sialyltransferases with various substrates. transfer to other substrates expressed relative to this in column 5 substrates within each antifreeze glycoprotein and IPNeu5AcGgOse4Cer as 100 ( ) for this group only in column expressed as % of N-acetyllactosamine or asialo-fetuin —, not determined.

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