Critical role of evolutionarily conserved glycosylation at Asn211 in the intracellular trafficking and activity of sialyltransferase ST3Gal-II

RUGGIERO F.M.; VILCAES A.; IGLESIAS-BARTOLOMÉ R.; DANIOTTI J.L.

Puerto Varas

Congreso; XXIX Annual Meeting of Chilean Society for Cell Biology; 2015

Chilean Society For Cell Biology

IntroductionST3Gal-II is the main mammalian sialyltransferase responsible for GD1a and GT1b ganglioside biosynthesis in brain. It contains two putative N-glycosylation sites (Asn92 and Asn211). The present study explores the occupancy of these potential N-glycosylation sites and its relevance for intracellular trafficking and enzyme activity in human ST3Gal-II. Materials and methodsConfocal microscopy. N-glycosylation and N-glycan trimming inhibition. Immunofluorescence. Site-directed mutagenesis. Enzymatic activity assays. ResultsST3Gal-II distributes along the Golgi complex (GC), mainly in proximal compartments. It is mostly N-glycosylated at Asn211 being this co-translational modification relevant for its exiting from the endoplasmic reticulum (ER), proper Golgi localization and enzymatic activity towards glycolipid and glycoprotein as acceptor substrates. Its N-terminal domain containing the cytosolic, transmembrane and stem region (aa 1-51) is able to drive a protein reporter out of the ER and to retain it at the GC. DiscussionWe demonstrated that ST3Gal-II is N-glycosylated at predicted N-glycosylation consensus sequences and revealed the role of this modification for its trafficking to the GC and for enzymatic activity. Nevertheless, ST3Gal-II N-glycosylation does not represent an absolute requirement for its GC retention. As the products of this sialyltransferase (GD1a and GT1b gangliosides) are glycolipid targets of autoantibodies associated with neuropathy syndromes, such as Guillain-Barré syndrome, inhibition of ST3Gal-II N-glycosylation might be considered as a potential target for neuropathology therapeutics.