6sni

Publication Abstract from PubMed

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 A 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 A 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.

Structure and mechanism of the ER-based glucosyltransferase ALG6.,Bloch JS, Pesciullesi G, Boilevin J, Nosol K, Irobalieva RN, Darbre T, Aebi M, Kossiakoff AA, Reymond JL, Locher KP Nature. 2020 Feb 26. pii: 10.1038/s41586-020-2044-z. doi:, 10.1038/s41586-020-2044-z. PMID:32103179^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.