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Publication Abstract from PubMed

All viruses depend on host cell proteins for replication. Denying viruses' access to the function of critical host proteins can result in antiviral activity against multiple virus families. In particular, small-molecule drug candidates which inhibit the alpha-glucosidase enzymes of the endoplasmic reticulum (ER) translation quality control (QC) pathway have demonstrated broad-spectrum antiviral activities and low risk for development of viral resistance. However, antiviral drug discovery focused on the ERQC enzyme alpha-glucosidase I (alpha-GluI) has been hampered by difficulties in obtaining crystal structures of complexes with inhibitors. We report here the identification of an orthologous enzyme from a thermophilic fungus, Chaetomium thermophilum (Ct), as a robust surrogate for mammalian ER alpha-GluI and a platform for inhibitor design. Previously annotated only as a hypothetical protein, the Ct protein was validated as a bona fide alpha-glucosidase by comparing its crystal structure to that of mammalian alpha-GluI, by demonstrating enzymatic activity on the unusual alpha-d-Glcp-(1 --> 2)-alpha-d-Glcp-(1 --> 3) substrate glycan, and by showing that well-known inhibitors of mammalian alpha-GluI (1-DNJ, UV-4, UV-5) also inhibit Ct alpha-GluI. Crystal structures of Ct alpha-GluI in complex with three such inhibitors (UV-4, UV-5, EB-0159) revealed extensive interactions with all four enzyme subsites and provided insights into the catalytic mechanism. Identification of ER Ct alpha-GluI as a surrogate for mammalian alpha-GluI will accelerate the structure-guided discovery of broad-spectrum antivirals. This study also highlights Ct as a source of thermostable eukaryotic proteins, such as ER alpha-Glu I, that lack orthologs in bacterial or archaeal thermophiles.

Identification of Endoplasmic Reticulum alpha-Glucosidase I from a Thermophilic Fungus as a Platform for Structure-Guided Antiviral Drug Design.,Karade SS, Kolesnikov A, Treston AM, Mariuzza RA Biochemistry. 2022 Apr 27. doi: 10.1021/acs.biochem.2c00092. PMID:35476408^[1]

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