Therapeutic Development in COVID-19

Taxonomic Characterization, Antiviral Activity and Induction of Three New Kenalactams in Nocardiopsis sp. CG3

Exploration of secondary metabolites secreted by new Actinobacteria taxa isolated from unexplored areas, can increase the possibility to obtain new compounds which can be developed into new drugs for the treatment of serious diseases such as hepatitis C. In this context, one actinobacterial strain, CG3, has been selected based on the results of polyphasic characterization, which indicate that it represents a new putative species within the genus Nocardiopsis. Two fractions (F2 and F3), prepared from the culture of strain CG3 in soybean medium, exhibited a pronounced antiviral activity against the HCV strain Luc-Jc1. LC–HRESIMS analysis showed different bioactive compounds in both active fractions (F2 and F3), including five polyenic macrolactams (kenalactams A-E), three isoflavone metabolites, along with mitomycin C and one p-phenyl derivative. Furthermore, feeding with 1% of methionine, lysine or alanine as a unique nitrogen source, induced the production of three novel kenalactam derivatives.

How Do Enveloped Viruses Exploit the Secretory Proprotein Convertases to Regulate Infectivity and Spread?

Inhibition of the binding of enveloped viruses surface glycoproteins to host cell receptor(s) is a major target of vaccines and constitutes an efficient strategy to block viral entry and infection of various host cells and tissues. Cellular entry usually requires the fusion of the viral envelope with host plasma membranes. Such entry mechanism is often preceded by “priming” and/or “activation” steps requiring limited proteolysis of the viral surface glycoprotein to expose a fusogenic domain for efficient membrane juxtapositions. The 9-membered family of Proprotein Convertases related to Subtilisin/Kexin (PCSK) serine proteases (PC1, PC2, Furin, PC4, PC5, PACE4, PC7, SKI-1/S1P, and PCSK9) participate in post-translational cleavages and/or regulation of multiple secretory proteins. The type-I membrane-bound Furin and SKI-1/S1P are the major convertases responsible for the processing of surface glycoproteins of enveloped viruses. Stefan Kunz has considerably contributed to define the role of SKI-1/S1P in the activation of arenaviruses causing hemorrhagic fever. Furin was recently implicated in the activation of the spike S-protein of SARS-CoV-2 and Furin-inhibitors are being tested as antivirals in COVID-19. Other members of the PCSK-family are also implicated in some viral infections, such as PCSK9 in Dengue. Herein, we summarize the various functions of the PCSKs and present arguments whereby their inhibition could represent a powerful arsenal to limit viral infections causing the present and future pandemics.