Cryo-electron microscopy structures of human oligosaccharyltransferase complexes OST-A and OST-B

Oligosaccharyltransferase (OST) catalyzes the transfer of a high-mannose glycan onto secretory proteins in the endoplasmic reticulum. Mammals express two distinct OST complexes that act in a cotranslational (OST-A) or posttranslocational (OST-B) manner. Here, we present high-resolution cryo-electron...

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Bibliographic Details
Published in:Science (American Association for the Advancement of Science) 2019-12, Vol.366 (6471), p.1372-1375
Main Authors: Ramírez, Ana S, Kowal, Julia, Locher, Kaspar P
Format: Article
Language:English
Subjects:
Asparagine
Catalytic subunits
Cryoelectron Microscopy
Division of labor
Electron microscopy
Endoplasmic reticulum
Glycan
Glycosylation
Hexosyltransferases - chemistry
High resolution
Humans
Mannose
Membrane Proteins - chemistry
Microscopy
Oligosaccharyltransferase
Protein Conformation
Protein Subunits - chemistry
Proteins
Substrates
Sugar
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Summary:Oligosaccharyltransferase (OST) catalyzes the transfer of a high-mannose glycan onto secretory proteins in the endoplasmic reticulum. Mammals express two distinct OST complexes that act in a cotranslational (OST-A) or posttranslocational (OST-B) manner. Here, we present high-resolution cryo-electron microscopy structures of human OST-A and OST-B. Although they have similar overall architectures, structural differences in the catalytic subunits STT3A and STT3B facilitate contacts to distinct OST subunits, DC2 in OST-A and MAGT1 in OST-B. In OST-A, interactions with TMEM258 and STT3A allow ribophorin-I to form a four-helix bundle that can bind to a translating ribosome, whereas the equivalent region is disordered in OST-B. We observed an acceptor peptide and dolichylphosphate bound to STT3B, but only dolichylphosphate in STT3A, suggesting distinct affinities of the two OST complexes for protein substrates.
ISSN:0036-8075
1095-9203
DOI:10.1126/science.aaz3505