Biosynthesis and characterisation of glycoproteins in Koliella antarctica (Klebsormidiales, Chlorophyta)

The biosynthesis of the oligosaccharide chains of glycoproteins in cultures of Koliella antarctica (Klebsormidiales), a green filamentous microalga collected from samples of seawater near the Italian station of Terra Nova (Ross Sea, Antarctica), has been studied by using D-[U-14C]glucosamine as a tracer. To characterize the oligosaccharide moieties of Koliella glycoproteins, immunolabelling experiments with different lectins have also been performed. The use of radioactive tracer has shown that exogenously supplied D-[U-14C]glucosamine is taken up by the microalga and sequentially metabolized to soluble radioactive UDP-N-acetylglucosamine and UDP-N-acetylgalactosamine. N-acetylglucosamine and N-acetylgalactosamine residues were incorporated mainly into the oligosaccharide chains of soluble and membrane-bound glycoproteins; the lowest amount of radioactive N-acetylhexosamines was detected in covalently and non-covalently linked cell-wall glycoproteins. Immunolabelling experiments with different lectins have shown similarities and differences among the patterns of soluble, membrane-bound and cell-wall glycoproteins. A peculiar characteristic of these microalgae is the presence of N-acetylgalactosamine residues as a component of the oligosaccharide chains of intracellular and cell wall N-linked glycoproteins.