Distinct <i>O</i>-Acetylation Patterns of Serum Glycoproteins among Humans, Mice, and Rats

<i>O</i>-Acetylation is a significant chemical modification of sialic acids on glycoproteins with diverse biological functions. As two important animal models, mice and rats have been widely used for various biomedical studies. In this study, we show that the sialic acid types and their <i>O</i>-acetylation patterns have large differences among serum glycoproteins of humans, rats, and mice. Based on intact <i>N</i>-glycopeptide analyses, all sialoglycopeptides in human sera were modified by Neu5Ac without any <i>O</i>-acetylation; 90% of sialoglycopeptides in rat sera were also modified by Neu5Ac, with more than 60% that were further <i>O</i>-acetylated. In contrast, 99% of sialoglycopeptides in mouse sera contained Neu5Gc including 12% in <i>O</i>-acetylated forms. Among all <i>O</i>-acetylated <i>N</i>-glycans, rat sera had hybrid glycans fivefold those of mouse sera, while mouse sera contained 5.5-fold core-fucosylated glycans and 4.6-31.5-fold mono-/penta-/hexa-antenna glycans compared to mice. The overall <i>O</i>-acetylation proportions of serum glycoproteins in rats were much higher than those in mice, and diverse <i>O</i>-acetylation proportions also commonly existed at different glycosites of the same glycoproteins. This study enhances our understanding of <i>O</i>-acetylated sialoglycan diversities and underscores the necessity of considering glycosylation profiles when selecting suitable animal models for various biomedical studies.