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Title | Structure and mechanism of the ER-based glucosyltransferase ALG6. |
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Journal, issue, pages | Nature, Vol. 579, Issue 7799, Page 443-447, Year 2020 |
Publish date | Feb 26, 2020 |
Authors | Joël S Bloch / Giorgio Pesciullesi / Jérémy Boilevin / Kamil Nosol / Rossitza N Irobalieva / Tamis Darbre / Markus Aebi / Anthony A Kossiakoff / Jean-Louis Reymond / Kaspar P Locher / |
PubMed Abstract | In eukaryotic protein N-glycosylation, a series of glycosyltransferases catalyse the biosynthesis of a dolichylpyrophosphate-linked oligosaccharide before its transfer onto acceptor proteins. The ...In eukaryotic protein N-glycosylation, a series of glycosyltransferases catalyse the biosynthesis of a dolichylpyrophosphate-linked oligosaccharide before its transfer onto acceptor proteins. The final seven steps occur in the lumen of the endoplasmic reticulum (ER) and require dolichylphosphate-activated mannose and glucose as donor substrates. The responsible enzymes-ALG3, ALG9, ALG12, ALG6, ALG8 and ALG10-are glycosyltransferases of the C-superfamily (GT-Cs), which are loosely defined as containing membrane-spanning helices and processing an isoprenoid-linked carbohydrate donor substrate. Here we present the cryo-electron microscopy structure of yeast ALG6 at 3.0 Å resolution, which reveals a previously undescribed transmembrane protein fold. Comparison with reported GT-C structures suggests that GT-C enzymes contain a modular architecture with a conserved module and a variable module, each with distinct functional roles. We used synthetic analogues of dolichylphosphate-linked and dolichylpyrophosphate-linked sugars and enzymatic glycan extension to generate donor and acceptor substrates using purified enzymes of the ALG pathway to recapitulate the activity of ALG6 in vitro. A second cryo-electron microscopy structure of ALG6 bound to an analogue of dolichylphosphate-glucose at 3.9 Å resolution revealed the active site of the enzyme. Functional analysis of ALG6 variants identified a catalytic aspartate residue that probably acts as a general base. This residue is conserved in the GT-C superfamily. Our results define the architecture of ER-luminal GT-C enzymes and provide a structural basis for understanding their catalytic mechanisms. |
External links | Nature / PubMed:32103179 / PubMed Central |
Methods | EM (single particle) |
Resolution | 3.0 - 3.9 Å |
Structure data | EMDB-10257, PDB-6snh: EMDB-10258, PDB-6sni: |
Chemicals | ChemComp-LMH: ChemComp-HOH: ChemComp-PTY: ChemComp-Y01: |
Source |
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Keywords | MEMBRANE PROTEIN / Glycosyltransferase / Glucosyltransferase / GT-C / N-Glycosylation |