Molecular cloning and characterization of lysosomal sialic acid O-acetylesterase

O-Acetylation and de-O-acetylation of sialic acids have been implicated in the regulation of a variety of biological phenomena, including endogenous lectin recognition, tumor antigenicity, virus binding, and complement activation. Applying a strategy designed to identify genes preferentially expressed in active sites of embryonic hematopoiesis, we isolated a novel cDNA from the pluripotent hematopoietic cell line FDCPmixA4 whose open reading frame contained sequences homologous to peptide fragments of a lysosomal sialic acid O-acetylesterase (Lse) previously purified from rat liver, but with no evident similarity to endoplasmic reticulum-derived acetylesterases. The expressed Lse protein exhibits sialic-acid O-acetylesterase activity that is not attributable to a typical serine esterase active site. lse expression is spatially and temporally restricted during embryogenesis, and its mRNA levels correlate with differences in O-acetylesterase activity described in adult tissues and blood cell types. Using interspecific backcross analysis, we further mapped the lse gene to the central region of mouse chromosome 9. This constitutes the first report on the molecular cloning of a sialic acid-specific O-acetylesterase in vertebrates and suggests novel roles for the 9-O-acetyl modification of sialic acids during the development and differentiation of mammalian organisms.