Post-Infection Entry Mechanism of Ricin A Chain-Pokeweed Antiviral Proteins (RTA-PAPs) Chimeras is Mediated by Viroporins

The limitations of virus-specific antiviral drugs became apparent during the current COVID-19 pandemic. The search for broad range antiviral proteins of a new kind to answer current and future pandemics has become an even more pressing matter. Here, the author further describes the expected anti-SARS-CoV-2 mechanisms of a novel broad range antiviral chimeric protein constructed between ricin A chain and pokeweed antiviral proteins. The latest in protein-ligand docking software were used to determine binding affinity of RTA-PAPs to SARS-CoV-2 frameshift stimulation element and elucidate the preferential post-infection entry mechanisms of RTA-PAPs into virus infected cells over non-infected ones, by doing a comparative analysis between in vitro and in silico results on numerous viruses. The results obtained strongly suggest that the post-infection preferential entry of RTA-PAPs into infected cells is mediated by the presence of viroporins integrated into the host cell membrane. The discovery of this mechanism revealed RTA-PAPs, and proteins like them, to be a new class of broad range antivirals that target with high specificity viroporin producing viruses, and with gain of functions in antiviral activities, post-infection.

Ricin Antibodies’ Neutralizing Capacity against Different Ricin Isoforms and Cultivars

Ricin, a highly toxic protein from Ricinus communis, is considered a potential biowarfare agent. Despite the many data available, no specific treatment has yet been approved. Due to their ability to provide immediate protection, antibodies (Abs) are an approach of choice. However, their high specificity might compromise their capacity to protect against the different ricin isoforms (D and E) found in the different cultivars. In previous work, we have shown the neutralizing potential of different Abs (43RCA-G1 (anti ricin A-chain) and RB34 and RB37 (anti ricin B-chain)) against ricin D. In this study, we evaluated their protective capacity against both ricin isoforms. We show that: (i) RB34 and RB37 recognize exclusively ricin D, whereas 43RCA-G1 recognizes both isoforms, (ii) their neutralizing capacity in vitro varies depending on the cultivar, and (iii) there is a synergistic effect when combining RB34 and 43RCA-G1. This effect is also demonstrated in vivo in a mouse model of intranasal intoxication with ricin D/E (1:1), where approximately 60% and 40% of mice treated 0 and 6 h after intoxication, respectively, are protected. Our results highlight the importance of evaluating the effectiveness of the Abs against different ricin isoforms to identify the treatment with the broadest spectrum neutralizing effect.

Novel Binding Mechanisms of Fusion Broad Range Anti-Infective Protein Ricin A Chain Mutant-Pokeweed Antiviral Protein 1 (RTAM-PAP1) against SARS-CoV-2 Key Proteins in Silico

The deadly pandemic named COVID-19, caused by a new coronavirus (SARS-CoV-2), emerged in 2019 and is still spreading globally at a dangerous pace. As of today, there are no proven vaccines, therapies, or even strategies to fight off this virus. Here, we describe the in silico docking results of a novel broad range anti-infective fusion protein RTAM-PAP1 against the various key proteins of SARS-CoV-2 using the latest protein-ligand docking software. RTAM-PAP1 was compared against the SARS-CoV-2 B38 antibody, ricin A chain, a pokeweed antiviral protein from leaves, and the lectin griffithsin using the special CoDockPP COVID-19 version. These experiments revealed novel binding mechanisms of RTAM-PAP1 with a high affinity to numerous SARS-CoV-2 key proteins. RTAM-PAP1 was further characterized in a preliminary toxicity study in mice and was found to be a potential therapeutic candidate. These findings might lead to the discovery of novel SARS-CoV-2 targets and therapeutic protein structures with outstanding functions.

Novel anti-SARS-CoV-2 mechanisms of fusion broad range anti- infective protein ricin A chain mutant-pokeweed antiviral protein 1 (RTAM-PAP1) in silico

A deadly pandemic named COVID-19 caused by a new coronavirus SARS- CoV-2 has emerged in 2019 and is still spreading globally at a dangerous pace. As of today, there are no proven vaccines, therapies or even strategies to fight off this virus. Here, we describe the in silico results of a novel broad range anti-infective fusion protein RTAM-PAP1 against the various key pro- teins of SARS-CoV-2 using the latest protein-ligand docking software. RTAM-PAP1 was compared against the SARS-CoV-2 B38 antibody, ricin A chain, pokeweed antiviral protein from leaves and the lectin griffithsin using CoDockPP special COVID-19 version. These experiments revealed novel binding mechanisms of RTAM-PAP1 with high affinity to numerous targets with anti-SARS-CoV-2 effects. RTAM-PAP1 was further characterized in a preliminary toxicity study in mice and was found to likely be a potent anti- SARS-CoV-2 agent. These findings might lead to the discovery of novel SARS-CoV-2 targets and therapeutic protein structures.

Novel anti-SARS-CoV-2 mechanisms of fusion broad range anti- infective protein ricin A chain mutant-pokeweed antiviral protein 1 (RTAM-PAP1) in silico

A deadly pandemic named COVID-19 caused by a new coronavirus SARS- CoV-2 has emerged in 2019 and is still spreading globally at a dangerous pace. As of today, there are no proven vaccines, therapies or even strategies to fight off this virus. Here, we describe the in silico results of a novel broad range anti-infective fusion protein RTAM-PAP1 against the various key pro- teins of SARS-CoV-2 using the latest protein-ligand docking software. RTAM-PAP1 was compared against the SARS-CoV-2 B38 antibody, ricin A chain, pokeweed antiviral protein from leaves and the lectin griffithsin using CoDockPP special COVID-19 version. These experiments revealed novel binding mechanisms of RTAM-PAP1 with high affinity to numerous targets with anti-SARS-CoV-2 effects. RTAM-PAP1 was further characterized in a preliminary toxicity study in mice and was found to likely be a potent anti- SARS-CoV-2 agent. These findings might lead to the discovery of novel SARS-CoV-2 targets and therapeutic protein structures.

Post-Exposure Anti-Ricin Treatment Protects Swine against Lethal Systemic and Pulmonary Exposures

Ricin, a plant-derived toxin originating from the seeds of Ricinus communis (castor bean plant), is one of the most lethal toxins known. To date, there is no approved post-exposure therapy for ricin exposures. This work demonstrates for the first time the therapeutic efficacy of equine-derived anti-ricin F(ab’)2 antibodies against lethal pulmonary and systemic ricin exposures in swine. While administration of the antitoxin at 18 h post-exposure protected more than 80% of both intratracheally and intramuscularly ricin-intoxicated swine, treatment at 24 h post-exposure protected 58% of the intramuscular-exposed swine, as opposed to 26% of the intratracheally exposed animals. Quantitation of the anti-ricin neutralizing units in the anti-toxin preparations confirmed that the disparate protection conferred to swine subjected to the two routes of exposure stems from variance between the two models. Furthermore, dose response experiments showed that approximately 3 times lesser amounts of antibody are needed for high-level protection of the intramuscularly compared to the intratracheally intoxicated swine. This study, which demonstrates the high-level post-exposure efficacy of anti-ricin antitoxin at clinically relevant time-points in a large animal model, can serve as the basis for the formulation of post-exposure countermeasures against ricin poisoning in humans.