ST3Gal-II and beta-4GalNT-I are S-acylated at N-terminal cysteines involved in homodimerization

Congreso; LII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB).; 2016

Ganglioside glycosyltransferases (GGTs) are type II membrane proteins that consist in a short N-terminal cytoplasmic tail, a transmembrane domain (TMD), and a luminally oriented C-terminal domain that bears the catalytic domain. We have previously shown that the N-terminal domain (Ntd) of the GGTs ST3Gal V, ST8Sia I and b4GalNT I are S-acylated at conserved cysteine residues when expressed in CHO-K1 cells. Here, we extended our studies to ST3Gal II, a GT that sialylates glycolipids and glycoproteins, and found that full length ST3Gal II is also S-acylated. S-acylation, commonly known as palmitoylation, is catalyzed by a family of palmitoyltransferases (PATs) that are mostly localized at the Golgi complex but also at the ER and the plasma membrane. Using GT?s ER-retention mutants, we found that S-acylation of b4GalNT I and ST3Gal II takes place at different compartments, suggesting that b4GalNT I and ST3Gal II are not substrates of the same PAT and this may be due to the different localization of the conserved cysteines in these GTs (TMD or cytosolic tail, respectively). We also found that cysteines that are target of S-acylation on b4GalNT I and ST3Gal II are involved in the formation of homodimers through disulfide bonds. We show an increase of ST3Gal II dimmers in the presence of the PAT inhibitor 2-bromopalmitate, suggesting that S-acylation may be regulating GTs homo-dimerization.