A C-Terminal Phosphatase Module Conserved in Vertebrate CMP-Sialic Acid Synthetases Provides a Tetramerization Interface for the Physiologically Active Enzyme

作者：Oschlies Melanie; Dickmanns Achim; Haselhorst Thomas; Schaper Wiebke; Stummeyer Katharina; Tiralongo Joe; Weinhold Birgit; Gerardy Schahn Rita; von Itzstein Mark; Ficner Ralf; Muenster Kuehnel Anja K

来源：Journal of Molecular Biology, 2009, 393(1): 83-97.

DOI：10.1016/j.jmb.2009.08.003

• sialic acid
• CMP-sialic acid
• CMP-sialic acid synthetase
• HAD phosphatase
• alpha/beta-type hydrolase fold

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 angstrom 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.

• 出版日期2009-10-16