La estabilidad de las proteínas modulan la eficiencia de la N-glicosilación postraduccional

COUTO, PAULA MONSERRAT; GUARDIA, CARLOS MANUEL ALBERTO; COUTO, FACUNDO LUIS; LABRIOLA, CARLOS ALBERTO; CARAMELO, JULIO JAVIER

Rosario

Congreso; LIX Reunión anual de la Sociedad Argentina de Investigaciones Bioquímicas; 2023

Sociedad Argentina de Investigaciones Bioquímicas

N-glycosylation is one of the most a frequent and drastic protein modifications, affecting nearly 25 % of the eukaryotic proteome. This process is carried out by the catalytic subunit (STT3) of the oligosaccharyl transferase complex, which adds a high mannose glycan to the lateral chain of Asn residues within the context Asn-X-Ser/Thr (X ≠ Pro), a motif known as N-glycosylation “sequon”. In metazoans, OST has two alternative STT3 subunits: STT3A and STT3B. OST with STT3A is associated with the SEC61 translocon and functions co-translationally. Vacant sequons have another opportunity for glycosylation by OST-carrying STT3B. However, the presence of an N-glycosylation sequon does not guarantee its full occupation by the OST. For this reason, a protein may present a mixture of partially occupied sequons, a phenomenon known as N-glycosylation macroheterogeneity. N-glycosylation efficiency depends on many factors, playing the chemical identity of the sequon a major role. Interestingly, identical sequons can display disparate occupancy levels. Here, we investigate the impact of the thermodynamic stability of acceptor proteins on this process. The occupancy of suboptimal sequons improves as the thermodynamic stability of the protein acceptors decreases. This effect is greatly pronounced in cells expressing only STT3B. Less stable proteins exhibit a slower rate of conformational maturation in vivo, which extends the time window for STT3B to operate. These findings can be explained by a kinetic model that distinguishes between local information within sequons and conformational maturation kinetics in vivo.