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Mitigation of the activity of the main protease (Mpro) and papain-like protease (PLpro) of SARS CoV-2 has direct implications in combating the ongoing deadly COVID-19 pandemic. The active site of these proteases contains cysteine thiols which are covalently modified by the sulfur drugs such as ebselen and disulfiram. The natural product of Allium contains several reactive sulfur compounds that may covalently modify the active site cysteine thiols of coronavirus proteases. The report has assessed the binding affinity of the 52 different sulfur compounds of Allium against both Mpro and PLpro of coronavirus by conventional docking methods. Three of the top six compounds have demonstrated high affinity for both the proteases, namely, E-ajoene (S3), S-(3-pentanyl)-L-cysteine-sulfoxide (S49), and 1-propenyl allyl thiosulfinate (S14). The reactive sulfur compounds E-ajoene and 1-propenyl allyl thiosulfinate were subjected to the calculation of energetics of the putative reactions and covalent docking studies. The results indicate they covalently modify the active site cysteine thiols of the proteases through S-thioallylation, S-thioallyl sulfinyl propenylation, and S-thiopropenylation. The diversity of covalent modifications, high affinity for both the proteases and sulfur-mediated hydrogen bonds at the active site indicate that E-ajoene is a potential dual protease targeting covalent inhibitor of SARS CoV-2. [ABSTRACT FROM AUTHOR]

Coronavirus disease 2019 (COVID-19) is an ongoing pandemic caused due to new coronavirus infection with 3716075 deaths across the world as reported by the World Health Organization (WHO). SARS-CoV-2 main protease (Mpro) plays a vital role in the replication of coronavirus and thus an attractive target for the screening of inhibitors for the therapy of COVID-19. The preclinical drugs ebselen and PX-12 are potent inhibitors of SARS-CoV-2 Mpro and covalently modifies the active site Cys-145 residue of Mpro through selenosulfide/disulfide. In the current report, using virtual screening methods, reactive sulfur species allicin is subjecting for covalent docking at the active site of SARS-CoV-2 Mpro using PX-12 as a benchmark reference compound. The results indicate that allicin induces dual S-thioallylation of Cys-145 and Cys-85/ Cys-156 residues of SARS-CoV-2 Mpro. Using density functional theory (DFT), Gibbs free energy change (DG) is calculated for the putative reactions between N-acetylcysteine amide thiol and allicin/allyl sulfenic acid. The overall reaction is exergonic and allyl disulfide of Cys-145 residue of Mpro is involved in a sulfur mediated hydrogen bond. The results indicate that allicin causes dual S-thioallylation of SARS-CoV-2 Mpro which may be of interest for treatment and attenuation of ongoing coronavirus infection. [ABSTRACT FROM AUTHOR]

The prevalence of methicillin-resitant Staphylococcus aureus (MRSA) in hospitals and the community poses an increasing health burden, which requires the discovery of alternative antimicrobials. Allicin (diallyl thiosulfinate) from garlic exhibits broad-spectrum antimicrobial activity against many multidrug resistant bacteria. The thiol-reactive mode of action of allicin involves its S -thioallylations of low molecular weight (LMW) thiols and protein thiols. To investigate the mode of action and stress response caused by allicin in S. aureus , we analyzed the transcriptome signature, the targets for S -thioallylation in the proteome and the changes in the bacillithiol (BSH) redox potential (E BSH) under allicin stress. Allicin caused a strong thiol-specific oxidative and sulfur stress response and protein damage as revealed by the induction of the PerR, HypR, QsrR, MhqR, CstR, CtsR, HrcA and CymR regulons in the RNA-seq transcriptome. Allicin also interfered with metal and cell wall homeostasis and caused induction of the Zur, CsoR and GraRS regulons. Brx-roGFP2 biosensor measurements revealed a strongly increased E BSH under allicin stress. In the proteome, 57 proteins were identified with S -thioallylations under allicin treatment, including translation factors (EF-Tu, EF-Ts), metabolic and redox enzymes (AldA, GuaB, Tpx, KatA, BrxA, MsrB) as well as redox-sensitive MarR/SarA-family regulators (MgrA, SarA, SarH1, SarS). Phenotype and biochemical analyses revealed that BSH and the HypR-controlled disulfide reductase MerA are involved in allicin detoxification in S. aureus. The reversal of protein S -thioallylation was catalyzed by the Brx/BSH/YpdA pathway. Finally, the BSSB reductase YpdA was shown to use S -allylmercaptobacillithiol (BSSA) as substrate to regenerate BSH in S. aureus. In conclusion, allicin results in an oxidative shift of E BSH and protein S -thioallylation, which can be reversed by YpdA and the Brx/BSH/YpdA electron pathways in S. aureus to regenerate thiol homeostasis. Image 1 • Allicin causes a thiol-specific oxidative stress response in S. aureus. • The mode of action of allicin involves S -thioallylation of 57 proteins. • S -thioallylated proteins are redox-sensitive enzymes and MarR-family regulators. • BSH and the disulfide reductase MerA are involved in allicin detoxification. • BrxAB/BSH/YpdA pathway functions in reversal of protein S-thioallylation. [ABSTRACT FROM AUTHOR]

Abstract A single clove of edible garlic (Allium sativum L.) of about 10 g produces up to 5 mg of allicin (diallylthiosulfinate), a thiol-reactive sulfur-containing defence substance that gives injured garlic tissue its characteristic smell. Allicin induces apoptosis or necrosis in a dose-dependent manner but biocompatible doses influence cellular metabolism and signalling cascades. Oxidation of protein thiols and depletion of the glutathione pool are thought to be responsible for allicin's physiological effects. Here, we studied the effect of allicin on post-translational thiol-modification in human Jurkat T-cells using shotgun LC-MS/MS analyses. We identified 332 proteins that were modified by S -thioallylation in the Jurkat cell proteome which causes a mass shift of 72 Da on cysteines. Many S -thioallylated proteins are highly abundant proteins, including cytoskeletal proteins tubulin, actin, cofilin, filamin and plastin-2, the heat shock chaperones HSP90 and HSPA4, the glycolytic enzymes GAPDH, ALDOA, PKM as well the protein translation factor EEF2. Allicin disrupted the actin cytoskeleton in murine L929 fibroblasts. Allicin stimulated the immune response by causing Zn2+ release from proteins and increasing the Zn2+-dependent IL-1-triggered production of IL-2 in murine EL-4 T-cells. Furthermore, allicin caused inhibition of enolase activity, an enzyme considered a cancer therapy target. In conclusion, our study revealed the widespread extent of S -thioallylation in the human Jurkat cell proteome and showed effects of allicin exposure on essential cellular functions of selected targets, many of which are targets for cancer therapy. Graphical abstract fx1 Highlights • Allicin from garlic caused S -thioallylation of 332 proteins in the human Jurkat cell proteome. • Main S -thioallylated proteins are cytoskeletal proteins, chaperones, glycolytic enzymes, translation factors. • Selected S -thioallylated proteins were shown to be inhibited by allicin. • Allicin disrupted the cytoskeleton, decreased enolase activity and enhanced Zn2+ release. • Mode of action of allicin in mammalian cells could explain its cytostatic effect in cancer cells. [ABSTRACT FROM AUTHOR]

Garlic is a common ingredient in food, normally used as spice but is also used since ancient times for its health beneficial activity. The thiosulfinate allicin is the first active compound in freshly damaged garlic tissue and reacts with thiol-groups. Hence, allicin is able to modify thiol groups, both of protein cysteine-residues and low-molecular weight thiols like glutathione. This thiol-modification is supposed to be an important mechanism for allicin’s biological activity. Here, the mechanisms and possible targets for allicin in cells are discussed.