The crystal structure of murine CMP-5-N-acetylneuraminic acid synthetase.
Sialic acids are activated by CMP-5-N-acetylneuraminic acid synthetase prior to their transfer onto oligo- or polysaccharides. Here, we present the crystal structure of the N-terminal catalytically active domain of the murine 5-N-acetylneuraminic acid synthetase in complex with the reaction product. In contrast to the previously solved structure of 5-N-acetylneuraminic acid synthetase from Neisseria meningitidis and the related CMP-KDO-synthetase of Escherichia coli, the murine enzyme is a tetramer, which was observed with the active sites closed. In this conformation a loop is shifted by 6A towards the active site and thus an essential arginine residue can participate in catalysis. Furthermore, a network of intermolecular salt-bridges and hydrogen bonds in the dimer as well as hydrophobic interfaces between two dimers indicate a cooperative behaviour of the enzyme. In addition, a complex regulation of the enzyme activity is proposed that includes phosphorylation and dephosphorylation.[1]References
- The crystal structure of murine CMP-5-N-acetylneuraminic acid synthetase. Krapp, S., Münster-Kühnel, A.K., Kaiser, J.T., Huber, R., Tiralongo, J., Gerardy-Schahn, R., Jacob, U. J. Mol. Biol. (2003) [Pubmed]
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