Reversible O-Acetyl Migration within the Sialic Acid Side Chain and Its Influence on Protein Recognition.

ACS chemical biology 2021 Oct 15

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O-Acetylation is a common naturally occurring modification of carbohydrates and is especially widespread in sialic acids, a family of nine-carbon acidic monosaccharides. O-Acetyl migration within the exocyclic glycerol-like side chain of mono-O-acetylated sialic acid reported previously was from the C7- to C9-hydroxyl group with or without an 8-O-acetyl intermediate, which resulted in an equilibrium that favors the formation of the 9-O-acetyl sialic acid. Herein, we provide direct experimental evidence demonstrating that O-acetyl migration is bidirectional, and the rate of equilibration is influenced predominantly by the pH of the sample. While the O-acetyl group on sialic acids and sialoglycans is stable under mildly acidic conditions (pH < 5, the rate of O-acetyl migration is extremely low), reversible O-acetyl migration is observed readily at neutral pH and becomes more significant when the pH increases to slightly basic. Sialoglycan microarray studies showed that esterase-inactivated porcine torovirus hemagglutinin-esterase bound strongly to sialoglycans containing a more stable 9-N-acetylated sialic acid analog, but these compounds were less resistant to periodate oxidation treatment compared to their 9-O-acetyl counterparts. Together with prior studies, the results support the possible influence of sialic acid O-acetylation and O-acetyl migration to host-microbe interactions and potential application of the more stable synthetic N-acetyl mimics.

Citation

Yang Ji, Aniruddha Sasmal, Wanqing Li, Lisa Oh, Saurabh Srivastava, Audra A Hargett, Brian R Wasik, Hai Yu, Sandra Diaz, Biswa Choudhury, Colin R Parrish, Darón I Freedberg, Lee-Ping Wang, Ajit Varki, Xi Chen. Reversible O-Acetyl Migration within the Sialic Acid Side Chain and Its Influence on Protein Recognition. ACS chemical biology. 2021 Oct 15;16(10):1951-1960