Products of endogenous N-acetylglucosaminyltransferase activity of Dictyostelium discoideum during growth and early development

Like animal cells, many unicellular eukaryotes modify mucin-like domains of secretory proteins with multiple O-linked glycans. Unlike animal mucin-type glycans, those of some microbial eukaryotes are initiated by ␣-linked GlcNAc rather than ␣-GalNAc. Based on sequence similarity to a recently cloned soluble polypeptide hydroxyproline GlcNAc-transferase that modifies Skp1 in the cytoplasm of the social ameba Dictyostelium, we have identified an enzyme, polypeptide ␣-N-acetylglucosaminyltransferase (pp ␣-GlcNAc-T2), that attaches GlcNAc to numerous secretory proteins in this organism. Unlike the Skp1 GlcNAc-transferase, pp ␣-GlcNAc-T2 is predicted to be a type 2 transmembrane protein. A highly purified, soluble, recombinant fragment of pp ␣-GlcNAc-T2 efficiently transfers GlcNAc from UDP-GlcNAc to synthetic peptides corresponding to mucin-like domains in two proteins that traverse the secretory pathway. pp ␣-GlcNAc-T2 is required for addition of GlcNAc to peptides in cell extracts and to the proteins in vivo. Mass spectrometry and Edman degradation analyses show that pp ␣-GlcNAc-T2 attaches GlcNAc in ␣-linkage to the Thr residues of all the synthetic mucin repeats. pp ␣-GlcNAc-T2 is encoded by the previously described modB locus defined by chemical mutagenesis, based on sequence analysis and complementation studies. This finding establishes that the many phenotypes of modB mutants, including a permeability defect in the spore coat, can now be ascribed to defects in mucin-type O-glycosylation. A comparison of the sequences of pp ␣-GlcNAc-T2 and the animal pp ␣-GalNAc-transferases reveals an ancient common ancestry indicating that, despite the different N-acetylhexosamines involved, the enzymes share a common mechanism of action.

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Products of endogenous N-acetylglucosaminyltransferase activity of Dictyostelium discoideum during growth and early development

Cited by 3 publications

References 27 publications

Glycosyltransferases in the Differentiation of Slime Molds

Glycosyltransferases in the Differentiation of Slime Molds

Bibliography on Dictyostelium

Initiation of Mucin-type O-Glycosylation in Dictyostelium Is Homologous to the Corresponding Step in Animals and Is Important for Spore Coat Function

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