PMID: 26687144

Authors:

Riemersma M, Froese DS, van Tol W, Engelke UF, Kopec J, van Scherpenzeel M, Ashikov A, Krojer T, von Delft F, Tessari M, Buczkowska A, Swiezewska E, Jae LT, Brummelkamp TR, Manya H, Endo T, van Bokhoven H, Yue WW, Lefeber DJ

Title:

Human ISPD Is a Cytidyltransferase Required for Dystroglycan O-Mannosylation.

Journal:

Chem Biol. 2015 Dec 17;22(12):1643-52. doi: 10.1016/j.chembiol.2015.10.014. Epub , 2015 Dec 10.

Abstract:

A unique, unsolved O-mannosyl glycan on alpha-dystroglycan is essential for its interaction with protein ligands in the extracellular matrix. Defective O-mannosylation leads to a group of muscular dystrophies, called dystroglycanopathies. Mutations in isoprenoid synthase domain containing (ISPD) represent the second most common cause of these disorders, however, its molecular function remains uncharacterized. The human ISPD (hISPD) crystal structure showed a canonical N-terminal cytidyltransferase domain linked to a C-terminal domain that is absent in cytidyltransferase homologs. Functional studies demonstrated cytosolic localization of hISPD, and cytidyltransferase activity toward pentose phosphates, including ribulose 5-phosphate, ribose 5-phosphate, and ribitol 5-phosphate. Identity of the CDP sugars was confirmed by liquid chromatography quadrupole time-of-flight mass spectrometry and two-dimensional nuclear magnetic resonance spectroscopy. Our combined results indicate that hISPD is a cytidyltransferase, suggesting the presence of a novel human nucleotide sugar essential for functional alpha-dystroglycan O-mannosylation in muscle and brain. Thereby, ISPD deficiency can be added to the growing list of tertiary dystroglycanopathies.