9-O-ACETYLATED SIALIC ACIDS HAVE WIDESPREAD BUT SELECTIVE EXPRESSION - ANALYSIS USING A CHIMERIC DUAL-FUNCTION PROBE DERIVED FROM INFLUENZA-C HEMAGGLUTININ-ESTERASE

While 9-O-acetylation of sialic acids has been reported in some mammal ian tissues, the distribution of this modification on specific cell ty pes and molecules is largely unknown. The influenza C virus hemaggluti nin-esterase is a membrane-bound glycoprotein that binds specifically to 9-O acetylated sialic acids (hemagglutinin activity) and then hydro lyzes the O-acetyl group (receptor-destroying activity). A recombinant soluble form of influenza C virus hemagglutinin-esterase wherein the C-terminal transmembrane and cytoplasmic domains are replaced by the F c portion of human IgG retains both its recognition and enzymatic func tions. The latter activity can selectively remove 9-O-acetyl groups fr om bound or free sialic acids and, under specific conditions, 7-O-acet yl groups as well. Irreversible inactivation of the esterase unmasks s table recognition activity, giving a molecule that binds specifically to 9-O-acetylated sialic acids. These probes demonstrate widespread bu t selective expression of 9-O-acetylated sialic acids in certain cell types of rat tissues. Patterns of polarized or gradient expression fur ther demonstrate the regulated nature of this modification. Direct pro bing of blots and thin-layer plates shows selective expression of 9-O- acetylation on certain glycoproteins and glycolipids in such tissues. Thus, 9-O-acetylation is more widespread than previously thought and o ccurs on specific molecules and cell types.