Novel Insights Into the Sulfated Glucuronic Acid-Based Anti-SARS-CoV-2 Mechanism of Exopolysaccharides From Halophilic Archaeon Haloarcula hispanica

Abstract

The pandemic caused by SARS-CoV-2 is the most widely spread disease in the 21st century. Due to the continuous emergence of variants across the world, it is necessary to expand our understanding of host–virus interactions and explore new agents against SARS-CoV-2. In this study, it was found exopolysaccharides (EPSs) from halophilic archaeon Haloarcula hispanica ATCC33960 can bind to the spike protein of SARS-CoV-2 with the binding constant KD of 2.23 nM, block the binding of spike protein to Vero E6 and bronchial epithelial BEAS-2B cells, and inhibit pseudovirus infection. However, EPSs from the gene deletion mutant △HAH_1206 almost completely lost the antiviral activity against SARS-CoV-2. A significant reduction of glucuronic acid (GlcA) and the sulfation level in EPSs of △HAH_1206 was clearly observed. Our results indicated that sulfated GlcA in EPSs is possible for a main structural unit in their inhibition of binding of SARS-CoV-2 to host cells, which would provide a novel antiviral mechanism and a guide for designing new agents against SARS-CoV-2.

AepG is a glucuronosyltransferase involved in acidic exopolysaccharide synthesis and contributes to environmental adaptation of Haloarcula hispanica

“…EPSs extracted from the parental strain consists of GlcA, Man, Gal, and Glc at a 4:3.6:1.5:1 M ratio. However, analysis of the EPS from the Δ HAH_1206 mutant showed only trace amounts of GlcA could be detected ( 35 ). To further assess whether HAH_1206 contributes to acidic EPS synthesis, DolP-linked sugars in the parental and mutant strains were extracted from the cell membrane, released with hydrofluoric acid, and analyzed by HPAEC-pulsed amperometric detection.…”

“…5 ), the sugar donors for the negatively charged sugars of the acidic EPS. Indeed, only trace amounts of GlcA could be detected in the EPS from the Δ HAH_1206 mutant ( 35 ). Therefore, it is reasonable to conclude that AepG is required for the synthesis of the negatively charged sugars of the acidic EPS, which is required for the separation and dispersal of H. hispanica cells in hypersaline surroundings.…”

“…Various haloarchaea produce EPSs ( 14 , 15 , 16 , 17 , 18 , 19 ), yet little is known about archaeal EPS biosynthesis. H. hispanica can produce an acidic EPS consisting of GlcA, Man, Gal, and Glc at a 4:3.6:1.5:1 M ratio ( 21 , 35 ), by a biosynthetic pathway that remains unknown.…”

“…We have shown that GlcA residues were not detected in the EPS of the Δ aepG mutant ( 35 ), which also lacked DolP-linked GlcA. Using recombinant CBD-AepG and the cell lysate of the mutant, we determined AepG activity in vitro .…”

Non-anticoagulant heparin derivatives for COVID-19 treatment

“…In preclinical studies of viral infections, heparin possesses a direct antiviral activity upon SARS-CoV-2. The early reports indicated that heparin could bind to the proteolytic cleavage site of the S1 and S2 protein based on combined surface plasmon resonance (SPR) and computational study [15] , [16] . Zhang et al found that heparin, HS, and non-anticoagulant low molecular weight heparin at micromolar doses could effectively compete with spike glycoprotein of COVID-19 to block the viral invasion pathway [17] .…”