Gangliosides are
sialic acid containing
glycosphingolipids, commonly found on the outer leaflet of the plasma membrane. O-acetylation of
sialic acid hydroxyl groups is one of the most common modifications in
gangliosides. Studies on the
biological activity of O-acetylated
gangliosides have been limited by their scarcity in nature. This comparatively small change in
ganglioside structure causes major changes in their physiological properties. When the
ganglioside GD1b was O-acetylated in the outer
sialic acid, it became the potent inhibitor of astroblast and
astrocytoma proliferation called
Neurostatin. Although various chemical and enzymatic methods to O-acetylate commercial
gangliosides have been described, O-acetylation was nonspecific and produced many side-products that reduced the yield. An
enzyme with O-
acetyltransferase activity (SOAT) has been previously cloned from the bacteria Campylobacter jejuni. This
enzyme catalyzed the acetylation of
oligosaccharide-bound
sialic acid, with high specificity for terminal alpha-2,8-linked residues. Using this
enzyme and commercial
gangliosides as starting material, we have specifically O-acetylated the
gangliosides' outer
sialic acids, to produce the corresponding
gangliosides specifically O-acetylated in the
sialic acid bound in alpha-2,3 and alpha-2,8 residues. We demonstrate here that O-acetylation occurred specifically in the C-9 position of the
sialic acid. In summary, we present a new method of specific O-acetylation of
ganglioside sialic acids that permits the large scale preparation of these modified
glycosphingolipids, facilitating both, the study of their mechanism of antitumoral action and their use as therapeutic drugs for treating
glioblastoma multiform (GBM) patients.