Post-translational N-glycosylation as a sensor of protein's conformational stability

GUARDIA CMA; COUTO PM; CARAMELO JJ; COUTO FL

San Martin, Buenos Aires

Simposio; Tercer Simposio Argentino de Glicobiología "GLYCOAR 2019"; 2019

UNSAM

N-glycosylation is one of the most frequent protein modificationsin eukaryotes. N-glycans fulfill multiple structural and biologicalfunctions, and are crucial for productive folding of manyglycoproteins. Carried out by the oligosaccharyltransferasecomplex (OST), the process consists in the transference of a highmannose glycan to the lateral chain of asparagine residues within the context ASN-X-SER/THR (where X cannot be PRO), a motif known as N-glycosylation sequon. In higher eukaryotes, there are two isoforms of the catalytic subunit of OST, STT3A and STT3B. While the activity of STT3A takes places mainly as N-glycosylation sequons appear in the ER lumen, STT3B occupies those sites left vacant after the initial round. However, the presence of a sequon does not guarantee its occupation by the OST, thus a protein could be present as a mixture of partially occupied sequons, a phenomenon known as N-glycosylation macroheterogeneity. It is known that some sequons are poorly recognized by the OST, for instance those displaying large hydrophobic and negatively charged residues in the middle. Even so, the molecular determinants for this behavior are largely unknown. Here we study the role of protein biosynthesis dynamics and folding on the modulation of this complex process. In particular, we could determine how protein´s thermodynamic stability affects the efficiency of post-translational N-glycosylation.