Summary As a major site of protein biosynthesis, homeostasis of the endoplasmic reticulum is critical for cell viability. Asparagine linked glycosylation of newly synthesized proteins by the oligosaccharyltransferase plays a central role in ER homeostasis due to the use of protein-linked oligosaccharides as recognition and timing markers for glycoprotein quality control pathways that discriminate between correctly folded proteins and terminally malfolded proteins destined for ER associated degradation. Recent findings indicate how the oligosaccharyltransferase achieves efficient and accurate glycosylation of the diverse proteins that enter the endoplasmic reticulum. In metazoan organisms two distinct OST complexes cooperate to maximize the glycosylation of nascent proteins. The STT3B complex glycosylates acceptor sites that have been skipped by the translocation channel associated STT3A complex.

The oxidoreductases activity of MagT1, an ER-localized thioredoxin homologue, is necessary for posttranslocational N-glycosylation of acceptor sites that lie proximal to cysteine residues.

In the frame of Multicenter observational study ECVD-RF (Epidemiology of Cardiovascular Diseases and their Risk Factors in Regions of Russian Federation) by the unique protocol the investigation of representative selections of adult population at the age of 25-64 y.o. of 11 regions RF (n=18305, including males, n=6919 and females n=11386): Volgograd, Vologda, Voronezh, Ivanovo, Kemerovo, Orenburg, Samara, Tomsk, Tyumen, Saint-Petersburg and Northern Osetia-Alania. The prevalence of the following risk factors (RF) of cardiovascular diseases is evaluated: high blood pressure — 33,8%, obesity — 29,7%, high total cholesterol — 57,6%, high glucose level or diabetes — 4,6%, smoking (tobacco consumption) — 25,7%, insufficient (low) level of physical activity — 38,8%, excessive salt consumption — 49,9% and insufficient vegetables and fruits consumption — 41,9%. Gender differences and an increase with the age of the parameters mentioned are described.The absence of a epidemiologic monitoring system at the Federal level leads to an impossibility of clear conclusions on the RF dynamics in Russian population. While comparing the ECVD-RF study with previous epidemiological studies we can just cautiously suppose the existence in 21st age of negative dynamics of one RF (obesity, dyslipidemia) and positive dynamics of the others (smoking).

Asparagine linked glycosylation of proteins is an essential protein modification reaction in most eukaryotic organisms. N-linked oligosaccharides are important for protein folding and stability, biosynthetic quality control, intracellular traffic and the physiological function of many Nglycosylated proteins. In metazoan organisms, the oligosaccharyltransferase is composed of a catalytic subunit (STT3A or STT3B) and a set of accessory subunits. Duplication of the catalytic subunit gene allowed cells to evolve OST complexes that act sequentially to maximize the glycosylation efficiency of the large number of proteins that are glycosylated in metazoan organisms. We will summarize recent progress in understanding the mechanism of (a) cotranslational glycosylation by the translocation channel associated STT3A complex, (b) the role of the STT3B complex in mediating cotranslational or posttranslocational glycosylation of acceptor sites that have been skipped by the STT3A complex, and (c) the role of the oxidoreductase MagT1 in STT3B-dependent glycosylation of cysteine-proximal acceptor sites.

Asparagine linked glycosylation of proteins is an essential protein modification reaction in most eukaryotic organisms. Metazoan organisms express two oligosaccharyltransferase complexes that are composed of a catalytic subunit (STT3A or STT3B) assembled with a shared set of accessory subunits and one to two complex specific subunits. siRNA mediated knockdowns of STT3A and STT3B in HeLa cells have shown that the two OST complexes have partially non-overlapping roles in N-linked glycosylation. However, incomplete siRNA mediated depletion of STT3A or STT3B reduces the impact of OST complex loss, thereby complicating the interpretation of experimental results. Here, we have used the CRISPR/Cas9 gene editing technology to create viable HEK293 derived cells lines that are deficient for a single catalytic subunit (STT3A or STT3B) or two STT3B-specific accessory subunits (MagT1 and TUSC3). Analysis of protein glycosylation in the STT3A, STT3B and MagT1/TUSC3 null cell lines revealed that these cell lines are superior tools for investigating the in vivo role and substrate preferences of the STT3A and STT3B complexes.