The atomic structure of a eukaryotic oligosaccharyltransferase complex.

Area of Science:

• Structural Biology
• Molecular Biology
• Biochemistry

Background:

• N-glycosylation is a vital post-translational modification affecting approximately 90% of eukaryotic glycoproteins.
• The oligosaccharyltransferase (OST) complex, located in the endoplasmic reticulum, catalyzes this essential process.
• Limited high-resolution structural data has hindered a deep understanding of eukaryotic protein N-glycosylation mechanisms.

Purpose of the Study:

• To determine the high-resolution structure of the Saccharomyces cerevisiae OST complex.
• To elucidate the structural basis of co-translational protein N-glycosylation.
• To provide insights for the potential development of small-molecule inhibitors targeting N-glycosylation.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was employed to achieve a 3.5 Å resolution structure of the OST complex.
• The structure determined encompasses key subunits including Ost1-Ost5, Stt3, Wbp1, and Swp1.

Main Results:

• The cryo-EM structure revealed the detailed architecture of the OST complex and its constituent subunits.
• Seven phospholipids were identified as mediators of inter-subunit interactions within the complex.
• An Stt3 N-glycan was observed to mediate interactions with Wbp1 and Swp1 in the ER lumen.
• Subunit Ost3 was found to interface with the Sec61 translocon, guiding nascent peptides to the catalytic site.

Conclusions:

• The high-resolution structure provides unprecedented insights into the mechanism of co-translational protein N-glycosylation.
• Understanding the OST complex structure and its interactions may pave the way for novel therapeutic strategies targeting glycosylation pathways.