A C-terminal phosphatase module conserved in vertebrate CMP-sialic acid synthetases provides a tetramerization interface for the physiologically active enzyme.
The biosynthesis of sialic acid-containing glycoconjugates is crucial for the development of vertebrate life. Cytidine monophosphate-sialic acid synthetase (CSS) catalyzes the metabolic activation of sialic acids. In vertebrates, the enzyme is chimeric, with the N-terminal domain harboring the synthetase activity. The function of the highly conserved C-terminal domain (CSS-CT) is unknown. To shed light on its biological function, we solved the X-ray structure of murine CSS-CT to 1.9 A resolution. CSS-CT is a stable shamrock-like tetramer that superimposes well with phosphatases of the haloacid dehalogenase superfamily. However, a region found exclusively in vertebrate CSS-CT appears to block the active-site entrance. Accordingly, no phosphatase activity was observed in vitro, which points toward a nonenzymatic function of CSS-CT. A computational three-dimensional model of full-length CSS, in combination with in vitro oligomerization studies, provides evidence that CSS-CT serves as a platform for the quaternary organization governing the kinetic properties of the physiologically active enzyme as demonstrated in kinetic studies.
Oschlies
Melanie
M
Institut für Zelluläre Chemie, Medizinische Hochschule Hannover, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany.
Dickmanns
Achim
A
Haselhorst
Thomas
T
Schaper
Wiebke
W
Stummeyer
Katharina
K
Tiralongo
Joe
J
Weinhold
Birgit
B
Gerardy-Schahn
Rita
R
von Itzstein
Mark
M
Ficner
Ralf
R
Münster-Kühnel
Anja-K
AK
D000595:Amino Acid Sequence; D000818:Animals; D018360:Crystallography, X-Ray; D007700:Kinetics; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D000216:N-Acylneuraminate Cytidylyltransferase / Q000737:chemistry* / Q000378:metabolism*; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
D000216:N-Acylneuraminate Cytidylyltransferase