Facts About: CMP-Sialic Acid in Nature

September 05, 2024

By: Richard D. Cummings

Sialic acid is a nonose (9-carbon) monosaccharide found in many organisms.  All vertebrates have sialic acid, while most invertebrates do not have sialic acid, but there are notable ones that do, as discussed below.  In addition, sialic acid is not generated nor found in glycoconjugates expressed by plants, parasites, protozoans and helminths (worms).  By contrast, many types of bacteria, such as E. coli K1 and Neisseria meningitidis, can synthesize Neu5Ac (1) and carry it within their surface glycoconjugates.  Colominic acid is an example of a polysaccharide comprised of α2-8-linked Neu5Ac made by E. coli K235 (2).  Amazingly, some parasites, such as the parasitic protozoan Trypanosoma spp, may acquire sialic acid from their host by a transglycosylation reaction using a ‘trans-sialidase’, which transfers sialic acid from host glycans to their own (3).

In animals and bacteria, CMP-sialic acid is the donor for sialylation reactions in synthesizing sialylated glycans.  It is made by the unique enzyme CMP-sialic acid synthetase, originally discovered by Roseman (4-6), in the same strain in which he also discovered CMP-sialic acid (7).  The vertebrate CMP-sialic acid synthetase is soluble, not membrane bound, and has two domains, an N-terminal domain that is catalytic and synthesizes CMP-sialic acid, and a C-terminal domain, whose function is to stabilize the enzyme (8-10).  Also of interest is that the mammalian CMP-sialic acid synthetase is located in the nucleus, whereas all other nucleotide sugar generating systems are in the cytoplasm (11,12). The mammalian enzyme, which has a catalytic N-terminal domain and a non-catalytic C-terminal domain, is targeted into the nucleus through nuclear localization signals within its polypeptide comprised of multiple clusters of basic amino acids (13).  By contrast, in Drosophila melanogaster the CMP-sialic acid synthetase is located in the Golgi apparatus, and is a single domain protein representing only the N-terminal catalytic domain (14,15).  The bacterial CMP-sialic acid synthetase is in the cytoplasm and has only a single catalytic domain.  In the fish medaka it has been found that a mutation in the C-terminal domain of CMP-sialic acid synthetase leads to dramatic loss of its activity due to instability of the protein, associated with the lethality 19 days post-fertilization, and abnormalities in ventricular contraction and skeletal myogenesis (16).  Although most glycans from Drosophila are not sialylated, some are, as reported in the early 1990s (17), though apparently at relatively low levels, but it is found on a variety of glycoproteins (18).

The importance of nuclear localization for the CMP-sialic acid synthetase is unclear.  All other nucleotide sugars are made in the cytoplasmic compartment and imported by specific transporters into the ER and Golgi (19).  There is also a specific transporter in the Golgi for import of CMP-sialic acid, suggesting that CMP-sialic acid made in the nucleus can accumulate in the cytoplasm for use by Golgi enzymes (20).  It is possible that the sequestration of CMP-sialic acid synthesis in the nuclear compartment is important in eukaryotes to limit its potential degradation, modifications (21,22), or other aspects of synthesis of sialylated molecules.  

References

  1. Vimr, E., and Lichtensteiger, C. (2002) To sialylate, or not to sialylate: that is the question. Trends Microbiol 10, 254-257

  2. Barry, G. T. (1958) Colominic acid, a polymer of N-acetylneuraminic acid. J Exp Med 107, 507-521

  3. Couto, A. S., Katzin, A. M., Colli, W., and de Lederkremer, R. M. (1987) Sialic acid in a complex oligosaccharide chain of the Tc-85 surface glycoprotein from the trypomastigote stage of Trypanosoma cruzi. Mol Biochem Parasitol 26, 145-153

  4. Mizanur, R. M., and Pohl, N. L. (2008) Bacterial CMP-sialic acid synthetases: production, properties, and applications. Appl Microbiol Biotechnol 80, 757-765

  5. Kean, E. L., Munster-Kuhnel, A. K., and Gerardy-Schahn, R. (2004) CMP-sialic acid synthetase of the nucleus. Biochim Biophys Acta 1673, 56-65

  6. Roseman, S. (1962) Enzymatic synthesis of cytidine 5'-mono-phospho-sialic acids. Proc Natl Acad Sci U S A 48, 437-441

  7. Comb, D. G., Watson, D. R., and Roseman, S. (1966) The sialic acids. IX. Isolation of cytidine 5'-monophospho-N-acetylneuraminic acid from Escherichia coli K-235. J Biol Chem 241, 5637-5642

  8. Oschlies, M., Dickmanns, A., Haselhorst, T., Schaper, W., Stummeyer, K., Tiralongo, J., Weinhold, B., Gerardy-Schahn, R., von Itzstein, M., Ficner, R., and Munster-Kuhnel, A. K. (2009) A C-terminal phosphatase module conserved in vertebrate CMP-sialic acid synthetases provides a tetramerization interface for the physiologically active enzyme. J Mol Biol 393, 83-97

  9. Mosimann, S. C., Gilbert, M., Dombroswki, D., To, R., Wakarchuk, W., and Strynadka, N. C. (2001) Structure of a sialic acid-activating synthetase, CMP-acylneuraminate synthetase in the presence and absence of CDP. J Biol Chem 276, 8190-8196

  10. Krapp, S., Munster-Kuhnel, A. K., Kaiser, J. T., Huber, R., Tiralongo, J., Gerardy-Schahn, R., and Jacob, U. (2003) The crystal structure of murine CMP-5-N-acetylneuraminic acid synthetase. J Mol Biol 334, 625-637

  11. Munster-Kuhnel, A. K., Tiralongo, J., Krapp, S., Weinhold, B., Ritz-Sedlacek, V., Jacob, U., and Gerardy-Schahn, R. (2004) Structure and function of vertebrate CMP-sialic acid synthetases. Glycobiology 14, 43R-51R

  12. Di, W., Fujita, A., Hamaguchi, K., Delannoy, P., Sato, C., and Kitajima, K. (2017) Diverse subcellular localizations of the insect CMP-sialic acid synthetases. Glycobiology 27, 329-341

  13. Munster, A. K., Weinhold, B., Gotza, B., Muhlenhoff, M., Frosch, M., and Gerardy-Schahn, R. (2002) Nuclear localization signal of murine CMP-Neu5Ac synthetase includes residues required for both nuclear targeting and enzymatic activity. J Biol Chem 277, 19688-19696

  14. Viswanathan, K., Tomiya, N., Park, J., Singh, S., Lee, Y. C., Palter, K., and Betenbaugh, M. J. (2006) Expression of a functional Drosophila melanogaster CMP-sialic acid synthetase. Differential localization of the Drosophila and human enzymes. J Biol Chem 281, 15929-15940

  15. Mertsalov, I. B., Novikov, B. N., Scott, H., Dangott, L., and Panin, V. M. (2016) Characterization of Drosophila CMP-sialic acid synthetase activity reveals unusual enzymatic properties. Biochem J 473, 1905-1916

  16. Wu, D., Arakawa, H., Fujita, A., Hashimoto, H., Hibi, M., Naruse, K., Kamei, Y., Sato, C., and Kitajima, K. (2021) A point-mutation in the C-domain of CMP-sialic acid synthetase leads to lethality of medaka due to protein insolubility. Sci Rep 11, 23211

  17. Roth, J., Kempf, A., Reuter, G., Schauer, R., and Gehring, W. J. (1992) Occurrence of sialic acids in Drosophila melanogaster. Science 256, 673-675

  18. Zhao, F., Jia, C., He, F., Hu, M., Guo, X., Zhang, J., and Feng, X. (2023) Site-Specific Profiling of N-Glycans in Drosophila melanogaster. Front Biosci (Landmark Ed) 28, 278

  19. Parker, J. L., Corey, R. A., Stansfeld, P. J., and Newstead, S. (2019) Structural basis for substrate specificity and regulation of nucleotide sugar transporters in the lipid bilayer. Nat Commun 10, 4657

  20. Zhao, W., Chen, T. L., Vertel, B. M., and Colley, K. J. (2006) The CMP-sialic acid transporter is localized in the medial-trans Golgi and possesses two specific endoplasmic reticulum export motifs in its carboxyl-terminal cytoplasmic tail. J Biol Chem 281, 31106-31118

  21. Visser, E. A., Moons, S. J., Timmermans, S., de Jong, H., Boltje, T. J., and Bull, C. (2021) Sialic acid O-acetylation: From biosynthesis to roles in health and disease. J Biol Chem 297, 100906

  22. Lewis, A. L., Chen, X., Schnaar, R. L., and Varki, A. (2022) Sialic Acids and Other Nonulosonic Acids. in Essentials of Glycobiology (Varki, A., Cummings, R. D., Esko, J. D., Stanley, P., Hart, G. W., Aebi, M., Mohnen, D., Kinoshita, T., Packer, N. H., Prestegard, J. H., Schnaar, R. L., and Seeberger, P. H. eds.), 4th Ed., Cold Spring Harbor (NY). pp 185-204

See also: Interesting Facts About Glycans