Structural Insights into the Broad-Spectrum Antiviral Target Endoplasmic Reticulum Alpha-Glucosidase II

Abstract

Targeting the host-cell endoplasmic reticulum quality control (ERQC) pathway is an effective broad-spectrum antiviral strategy. The two ER resident α-glucosidases whose sequential action permits entry in this pathway are the targets of glucomimetic inhibitors. Knowledge of the molecular details of the ER α-glucosidase II (α-Glu II) structure was limited. We determined crystal structures of a trypsinolytic fragment of murine α-Glu II, alone and in complex with key catalytic cycle ligands, and four different broad-spectrum antiviral iminosugar inhibitors, two of which are currently in clinical trials against dengue fever. The structures highlight novel portions of the enzyme outside its catalytic pocket which contribute to its activity and substrate specificity. These crystal structures and hydrogen-deuterium exchange mass spectrometry of the murine ER alpha glucosidase II heterodimer uncover the quaternary arrangement of the enzyme's α- and β-subunits, and suggest a conformational rearrangement of ER α-Glu II upon association of the enzyme with client glycoproteins.

Modulation of ERQC and ERAD: A Broad-Spectrum Spanner in the Works of Cancer Cells?

“…Entry into ERQC is conditional on ER α Glu II-mediated removal of the terminal Glc from the Glc 2 Man 9 GlcNAc 2 glycan, enabling recruitment of the resulting monoglucosylated glycoprotein to the ER lectins calnexin and calreticulin, and the associated oxido-reductases, isomerases, and foldases. The same ER α Glu II eventually removes the remaining Glc from the Glc 1 Man 9 GlcNAc 2 glycan, preventing further association with the ER lectins, thus freeing a glycoprotein from the refolding end of ERQC [37]. The noncatalytic ER α Glu II β subunit likely mediates association with the client glycoprotein glycan via its C-terminal mannose 6-phosphate receptor homology (MRH) domain, and it contains the ER-retrieval motif localising ER α Glu II to the ER [38].…”

Phylogenetic Characterization of Arboviruses in Patients Suffering from Acute Fever in Rondônia, Brazil

“…The term arbovirus ( Arthropod-Borne Virus ) refers to a group of different virus families that are transmitted by arthropod vectors, such as mosquitoes, ticks and flies [ 1 , 2 ]. Although arboviruses develop a natural zoonotic cycle, involving the virus, its vectors, non-human vertebrate hosts and the environment [ 3 ], they are transmitted to humans accidentally or to other vertebrates during the bite by an infected vector.…”

Characterizing the selectivity of ER α-glucosidase inhibitors

“…The simplest explanation for these findings is that 3,7a-ALX is a selective inhibitor of ER α-Glu I and all our data are consistent with this hypothesis. Furthermore, the key residues implicated in substrate binding (Caputo et al 2016, 2018; Satoh et al 2016) are conserved between the C. thermophilum and canine alpha-subunits of ER α-Glu II (Supplementary Figure S5), suggesting that our data with the purified enzyme is directly relevant to our microsome based studies. Nevertheless, although we tentatively suggest that 3,7a-ALX may be a selective inhibitor of ER α-Glu I, further experiments, such as studies using purified ER α-Glu I, will be required to confirm this hypothesis.…”

“…Figures 3 and 4), and both studies locate the putative enzyme active site in the center of a highly conserved (β/α) 8 barrel domain (Supplementary Figure S5). The murine and C. thermophilum GIIα proteins have a similar domain architecture and the respective positioning of bound disaccharides is well matched (Caputo et al 2018). Given its close similarity to both the canine (92% sequence identity) and human (90% sequence identity) proteins, we utilized the mouse GIIα structure in our docking studies in the hope of obtaining information of potential therapeutic value.…”