Alterations in sialic-acid O-acetylation glycoforms during murine erythrocyte development

Vinay S. Mahajan; Faisal Alsufyani; Hamid Mattoo; Ian Rosenberg; Shiv Pillai

Prior studies of Baumann et al have shown that CASD1 catalyzes the transfer of acetyl moieties from acetyl-CoA to CMP-sialic acid through the formation of a covalent acetyl-enzyme intermediate (Baumann et al., 2015) . Of note, CASD1 is unable to use . CC-BY-NC-ND 4.0 International license is made available under a The copyright holder for this preprint (which was not peer-reviewed) is the author/funder. It . https://doi.org/10.1101/469254 doi: bioRxiv preprint the unactivated form of sialic acid or other sialic acid that is already incorporated into sialoconjugates (e.g. fetuin (N-linked), bovine submandibular mucin (O-linked), 2,3/2,6sialolactose, or GD3) as substrates. The authors proposed that the 9-O-acetylated CMPsialic acid is subsequently incorporated into sialoglycans. CASD1 is widely expressed in most tissues (based on the Protein and RNA Expression Atlas); this may indicate that The copyright holder for this preprint (which was not peer-reviewed) is the author/funder. It . https://doi.org/10.1101/469254 doi: bioRxiv preprint Based on our analysis of the differential binding or inactivation of the TER-119 epitope by BHE and CHE virolectins and receptor-destroying esterases, the TER-119 antibody appears to recognize an epitope bearing 7,9-di-O-acetyl sialic acid. The analysis of the ligand-bound structures of BHE and CHE shows that although there is some structural homology between the two hemagglutinins, they bind the 9-O-acetyl sialic acid ligand in opposite orientations (Zeng et al., 2008) . Thus, it is theoretically possible that the conformation of the specific 9-O-acetyl sialic acid glycoform recognized by TER-119 is sterically constrained in the context of a particular glycan that favors binding and recognition by BHE over CHE. Although both BHE and CHE are lectins fused to receptor-destroying enzymes, it is particularly interesting that the esterase and hemagglutinin activities appear to have evolutionarily converged at the level of the specific glyco-conformations of 9-O-acetyl sialic acids. Thus study reveals an additional layer of complexity and diversity among the O-acetylated sialic acids and establishes the developmental regulation of the sequential acquisition of two different forms of 9-Oacetyl sialic acid during murine erythroid differentiation.