ST3Gal-II and b4GalNT-I are S-acylated at N-terminal cysteines involved in homo-dimerization

FERNANDO M. RUGGIERO; SABRINA CHUMPEN RAMIREZ; JAVIER VALDEZ TAUBAS; JOSE L. DANIOTTI

Córdoba

Congreso; "LII Reunión anual de SAIB"; 2016

Sociedad Argentina de Investigación Bioquímica

Ganglioside glycosyltransferases (GGTs) are type IImembrane proteins that consist in a short N-terminal cytoplasmic tail, atransmembrane domain (TMD), and a luminally oriented C-terminal domain thatbears 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 conservedcysteine residues when expressed in CHO-K1 cells. Here, we extended our studiesto ST3Gal II, a GT that sialylates glycolipids and glycoproteins, and foundthat full length ST3Gal II is also S-acylated. S-acylation, commonly known aspalmitoylation, is catalyzed by a family of palmitoyltransferases (PATs) thatare mostly localized at the Golgi complex but also at the ER and the plasmamembrane. Using GT?s ER-retention mutants, we found that S-acylation of b4GalNTI and ST3Gal II takes place at different compartments, suggesting that b4GalNTI and ST3Gal II are not substrates of the same PAT and this may be due to thedifferent localization of the conserved cysteines in these GTs (TMD orcytosolic tail, respectively). We also found that cysteines that are target ofS-acylation on b4GalNT I and ST3Gal II are involved in the formation ofhomodimers through disulfide bonds. We show an increase of ST3Gal II dimmers inthe presence of the PAT inhibitor 2-bromopalmitate, suggesting that S-acylationmay be regulating GTs homo-dimerization.