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Nat Commun. 2015 Jul 14;6:7673. doi: 10.1038/ncomms8673.

9-O-Acetylation of sialic acids is catalysed by CASD1 via a covalent acetyl-enzyme intermediate.

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Institute of Cellular Chemistry, Hannover Medical School, D-30623 Hannover, Germany.
Virology Division, Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, 3584 CH Utrecht, The Netherlands.


Sialic acids, terminal sugars of glycoproteins and glycolipids, play important roles in development, cellular recognition processes and host-pathogen interactions. A common modification of sialic acids is 9-O-acetylation, which has been implicated in sialoglycan recognition, ganglioside biology, and the survival and drug resistance of acute lymphoblastic leukaemia cells. Despite many functional implications, the molecular basis of 9-O-acetylation has remained elusive thus far. Following cellular approaches, including selective gene knockout by CRISPR/Cas genome editing, we here show that CASD1--a previously identified human candidate gene--is essential for sialic acid 9-O-acetylation. In vitro assays with the purified N-terminal luminal domain of CASD1 demonstrate transfer of acetyl groups from acetyl-coenzyme A to CMP-activated sialic acid and formation of a covalent acetyl-enzyme intermediate. Our study provides direct evidence that CASD1 is a sialate O-acetyltransferase and serves as key enzyme in the biosynthesis of 9-O-acetylated sialoglycans.

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