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. 2021 Dec 17;12:799861. doi: 10.3389/fimmu.2021.799861

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Copyright © 2021 Hugonnet, Singh, Haas and von Gunten

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Sialic acids. Sialic acids are nine-carbon monosaccharides. (A) The two main mammalian sialic acids N-acetyl neuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc) are shown. Neu5Gc is derived from Neu5Ac and differs by one oxygen atom in the N-glycolyl group, which is added by the enzyme cytidine monophosphate N-acetylneuraminic acid hydroxylase (CMAH) in the cytosol. Humans have an inactivating mutation of the CMAH gene and therefore they lack this enzymatic activity. (B) Kdn (2-keto-3-deoxy-D-glycero-D-galacto-nononic acid), which is more common among lower vertebrates and bacteria (see text).