8pn9
From Proteopedia
Structure of human oligosaccharyltransferase OST-A complex bound to NGI-1
Structural highlights
DiseaseSTT3A_HUMAN STT3A-CDG. The disease is caused by mutations affecting the gene represented in this entry. FunctionSTT3A_HUMAN Catalytic subunit of the oligosaccharyl transferase (OST) complex that catalyzes the initial transfer of a defined glycan (Glc(3)Man(9)GlcNAc(2) in eukaryotes) from the lipid carrier dolichol-pyrophosphate to an asparagine residue within an Asn-X-Ser/Thr consensus motif in nascent polypeptide chains, the first step in protein N-glycosylation. N-glycosylation occurs cotranslationally and the complex associates with the Sec61 complex at the channel-forming translocon complex that mediates protein translocation across the endoplasmic reticulum (ER). All subunits are required for a maximal enzyme activity. This subunit contains the active site and the acceptor peptide and donor lipid-linked oligosaccharide (LLO) binding pockets (By similarity). STT3A is present in the majority of OST complexes and mediates cotranslational N-glycosylation of most sites on target proteins, while STT3B-containing complexes are required for efficient post-translational glycosylation and mediate glycosylation of sites that have been skipped by STT3A (PubMed:19167329).[UniProtKB:P39007][1] Publication Abstract from PubMedNuclear factor kappaB (NF-kappaB) plays roles in various diseases. Many inflammatory signals, such as circulating lipopolysaccharides (LPSs), activate NF-kappaB via specific receptors. Using whole-genome CRISPR-Cas9 screens of LPS-treated cells that express an NF-kappaB-driven suicide gene, we discovered that the LPS receptor Toll-like receptor 4 (TLR4) is specifically dependent on the oligosaccharyltransferase complex OST-A for N-glycosylation and cell-surface localization. The tool compound NGI-1 inhibits OST complexes in vivo, but the underlying molecular mechanism remained unknown. We did a CRISPR base-editor screen for NGI-1-resistant variants of STT3A, the catalytic subunit of OST-A. These variants, in conjunction with cryoelectron microscopy studies, revealed that NGI-1 binds the catalytic site of STT3A, where it traps a molecule of the donor substrate dolichyl-PP-GlcNAc(2)-Man(9)-Glc(3), suggesting an uncompetitive inhibition mechanism. Our results provide a rationale for and an initial step toward the development of STT3A-specific inhibitors and illustrate the power of contemporaneous base-editor and structural studies to define drug mechanism of action. Positive selection CRISPR screens reveal a druggable pocket in an oligosaccharyltransferase required for inflammatory signaling to NF-kappaB.,Lampson BL, Ramiotarez AS, Baro M, He L, Hegde M, Koduri V, Pfaff JL, Hanna RE, Kowal J, Shirole NH, He Y, Doench JG, Contessa JN, Locher KP, Kaelin WG Jr Cell. 2024 Apr 25;187(9):2209-2223.e16. doi: 10.1016/j.cell.2024.03.022. PMID:38670073[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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