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

Córdoba

Congreso; "LII Reunión anual de SAIB"; 2016

Sociedad Argentina de Investigación Bioquímica

Ganglioside glycosyltransferases (GGTs) are type-II integral membrane proteins that consist of 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 beta4GalNT-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 at the Ntd cysteine residue. Using ER-retention mutants we found that S-acylation of beta4GalNT-I and ST3Gal-II occurs at different compartments. S-acylation 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. Our results suggest that beta4GalNT-I and ST3Gal-II are substrates of different PATs which could be determined by the localization of the conserved cysteine, within the TMD or outside of it. We also found that cysteines target of S-acylation on beta4GalNT-I and ST3Gal-II are also involved in the formation of homodimers through disulfide bonds. We could demonstrate an increase of ST3Gal-II dimmers in the presence of the PAT inhibitor 2-bromopalmitate, suggesting that S-acylation could be regulating GTs homodimerization.