Download MendeleyStructure and mechanism of the ER-based glucosyltransferase ALG6.
Bloch, J.S., Pesciullesi, G., Boilevin, J., Nosol, K., Irobalieva, R.N., Darbre, T., Aebi, M., Kossiakoff, A.A., Reymond, J.L., Locher, K.P.(2020) Nature 579: 443-447
- PubMed: 32103179
- DOI: https://doi.org/10.1038/s41586-020-2044-z
- Primary Citation of Related Structures:
6SNH, 6SNI - 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 1 . The final seven steps occur in the lumen of the endoplasmic reticulum (ER) and require dolichylphosphate-activated mannose and glucose as donor substrates 2 . 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 3,4 . 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.
Organizational Affiliation:
Institute of Molecular Biology and Biophysics, ETH Zürich, Zürich, Switzerland.
