Sialic acids synthesis

Paccalet, T. et al. (2007). Engineering of a sialic acid synthesis pathway in transgenic plants by expression of bacterial Neu5AC-synthesizing enzymes. Plant Biotechnol. J. 5(1) 16-25. 

Scheme 2.2.5.23 Alternative pathways for sialic acid synthesis using the catabolic aldolase (NeuA) or the anabolic synthase (NeuS) enzymes.

H. LOnn and K. Stenvall, Exceptionally high yield in glycosylation with sialic acid. Synthesis of a GM3 glycoside, Tetrahedron Lett. 33 115 (1992). 

Ando H, Ishida H, Kiso M, Hasegawa A. A synthetic approach to the c-series gangliosides containing sialyl-alpha(2-8)sialyl-alpha (2-8)sialic acid synthesis of ganglioside GT4, alpha(2-6) GT4 and GT3. Carbohydr. Res. 1997 300 207-217. 

Immobilized enzymes are often more stable than the soluble counterparts and can be recycled. They are also removable from a reaction mixture. PHA synthase fusions with the enzyme of interest were successfully developed and enabled production of recombinant enzyme already attached to a support material (PHA) in one step. The fl-galactosidase LacZ [21] was the first immobilized enzyme followed by alpha-amylase, organophosphohydrolase, and enzymes involved in sialic acid synthesis [76-78]. These demonstrated applicability PHA-immobilized enzymes in food processing, biomass conversion, bioremediation, and fine chemical synthesis. 

The preceding sections have dealt almost exclusively with glycoprotein synthesis by normal liver. As mentioned earlier, there is much interest in the increased rate of plasma glycoprotein synthesis that occurs in many pathological states (Winzler, 1968 Bocci, 1970). Under other conditions such as protein deficiency (Neuhaus et al., 1963) or choline deficiency (Mookerjea, 1969 Mookerjea et al., 1967), there is a decrease in plasma glycoprotein synthesis. Feedback inhibition has been demonstrated in the pathways of UDP-N-acetylglucosamine and CMP-sialic acid synthesis (Kornfeld et al., 1964). There have been reports that vitamin K (Johnson et al., 1971 Bernacki and Bosmann, 1970) and vitamin A (DeLuca... 

Another pharmacologic option is the use of metabolites involved in the sialic acid biosynthetic pathway. This is theoretically possible as the function of other enzymes involved in sialic acid synthesis is not affected in cells with GNE mutations, suggesting that metabolite supplementation may be an effective option in increasing sialic acid levels. This possibility is further supported by studies on the recovery of cellular sialylation after supplementation with ManNAc or sialic acid [26, 40]. 

Figure 11.3 Incorporation of exogenous sialic acid metabolites into the pathway for sialic acid synthesis. Mutations in the GNE gene cause reduced GlcNAc epimerase and ManNAc kinase enzymatic activities, which can be rescued by supplementation with sialic acid metabolites. ManNAc or NeuAc can be incorporated...

FIGURE 12. Sialic acid synthesis by the procedure of Kuhn and Baschang 962b)... 

A basically different approach to sialic acid synthesis was recently described by Mirzayanova et al. (1970) (Figure 13). N-Acetyl-o-manno-samine was subjected to the cyanohydrin reaction, the cyano group converted to an aldehyde, and the latter condensed with phosphorane XLVII via the Wittig reaction. Mild hydrolysis gave a crystalline product that was identical to natural NANA in elemental analysis, optical rotation, melting point, chromatographic behavior, and color reactions. 

Another, more classical, control mechanism exists for the feedback regulation of key enzymes for the synthesis of Gm-6-P04 and for N-acetylmannosamine. Each of these is the first enzyme in the metabolic commitment to hexosamine and sialic acid synthesis. Komfeld et al, (1964) showed that UDP-GlcNAc is an efficient feedback inhibitor for L-glutamine-D-fructose-6-phosphate aminotransferase and that CMP-NAN also inhibits UDP-GlcNAc-2-epimerase, which is responsible for the synthesis of A/ -acetylmannosamine. This is an example of the by now familar endproduct inhibition of the first enzyme of a metabolic pathway (see Figure 6). They were also able to demonstrate that in vivo administration of puromycin to rats, which inhibits de novo protein synthesis and also depresses sialic acid and hexosamine utilization, does not lead to an accumulation of UDP-GlcNAc. Furthermore, the turnover of the UDP-hexosamine pool was shown to be slowed down. These data suggest that impairment of the utilization of UDP-hexosamine leads to decreased synthesis of UDP-hexosamines or their precursors (i.e., classical feedback inhibition). 

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