SARS-CoV-2 Main Protease Targets Host Selenoproteins and Glutathione Biosynthesis for Knockdown via Proteolysis, Potentially Disrupting the Thioredoxin and Glutaredoxin Redox Cycles

Abstract

Associations between dietary selenium status and the clinical outcome of many viral infections, including SARS-CoV-2, are well established. Multiple independent studies have documented a significant inverse correlation between selenium status and the incidence and mortality of COVID-19. At the molecular level, SARS-CoV-2 infection has been shown to decrease the expression of certain selenoproteins, both in vitro and in COVID-19 patients. Using computational methods, our group previously identified a set of six host proteins that contain potential SARS-CoV-2 main protease (Mpro) cleavage sites. Here we show experimentally that Mpro can cleave four of the six predicted target sites, including those from three selenoproteins: thioredoxin reductase 1 (TXNRD1), selenoprotein F, and selenoprotein P, as well as the rate-limiting enzyme in glutathione synthesis, glutamate-cysteine ligase catalytic subunit (GCLC). Cleavage was assessed by incubating recombinant SARS-CoV-2 Mpro with synthetic peptides spanning the proposed cleavage sites, and analyzing the products via UPLC-MS. Furthermore, upon incubation of a recombinant Sec498Ser mutant of the full TXNRD1 protein with SARS-CoV-2 Mpro, the predicted cleavage was observed, destroying the TXNRD1 C-terminal redox center. Mechanistically, proteolytic knockdown of both TXNRD1 and GCLC is consistent with a viral strategy to inhibit DNA synthesis, conserving the pool of ribonucleotides for increased virion production. Viral infectivity could also be enhanced by GCLC knockdown, given the ability of glutathione to disrupt the structure of the viral spike protein via disulfide bond reduction. These findings shed new light on the importance of dietary factors like selenium and glutathione in COVID-19 prevention and treatment.

Selenium—More than Just a Fortuitous Sulfur Substitute in Redox Biology

“…The impairment of antioxidant defense is due to SARS-CoV-2 infection. Selenium and selenoproteins play a major role in combating oxidative stress in response to SARS-CoV-2 infections [ 324 , 325 ]. Several experiments from different countries have demonstrated that low serum levels are present in COVID-19 patients [ 326 , 327 ].…”

“…Interestingly, GP X 1 significantly binds with the inactive Mpro mutant (C145A), but no interaction is observed between GPx1 and wild-type Mpro [ 342 , 343 ]. Based on this, Gallardo et al investigated experimentally the cleavage of the GPx1 10-mer peptide by Mpro, but no cleavage was observed [ 324 ]. It can be concluded that selenocysteine is significantly different from glutamine at the cleavage site.…”

Funktionen eines Spurenelements

“…Die Arbeitsgruppe von Ethan Will Taylor an der University of North Carolina in Greensboro, USA, hat vor kurzem einen mechanistischen Zusammenhang zwi-schen dem Covid-Virus Sars-CoV-2 und dem Selenstoffwechsel nachgewiesen. 3) Vorher gab es Hinweise darauf, dass Viren die Produktion von Selenoproteinen behindern, indem sie in die Genregulation eingreifen. Nach den neuen Ergebnissen gehen sie gegen die Proteine selbst vor: Den Forscher:innen zufolge spaltet die Protease des Virus drei menschliche Selenoproteine und macht sie damit funktionsuntüchtig.…”

The relevance of selenium to viral disease with special reference to SARS-CoV-2 and COVID-19

“…Other strong candidates for proteolysis by Mpro included sites in TXNRD1 and SELENOP. Synthetic peptides corresponding to all three of these putative cleavage sites in human selenoproteins have been found to be cleaved in vitro by recombinant Mpro using synthetic peptides and MS to identify the cleavage products (80) .…”