Heterologous Expression and Partial Characterization of a Putative Opine Dehydrogenase from a Metagenomic Sequence of Desulfohalobium retbaense

The aim of this research was to prove the function of the putative opine dehydrogenase from Desulfohalobium retbaense and to characterize the enzyme in terms of functional and kinetic parameters. A putative opine dehydrogenase was identified from a metagenomic library by a sequence-based technique search of the metagenomic library, and afterward was successfully heterologously produced in Escherichia coli. In order to examine its potential for applications in the synthesis of secondary amines, first the substrate specificity of the enzyme towards different amino donors and amino acceptors was determined. The highest affinity was observed towards small amino acids, preferentially L-alanine, and when it comes to α-keto acids, pyruvate proved to be a preferential amino acceptor. The highest activity was observed at pH 6.5 in the absence of salts. The enzyme showed remarkable stability in a wide range of experimental conditions, such as broad pH stability (from 6.0-11.0 after 30 min incubation in buffers at a certain pH), stability in the presence of NaCl up to 3.0 M for 24 h, it retained 80 % of the initial activity after 1 h incubation at 45 °C, and 65 % of the initial activity after 24 h incubation in 30 % dimethyl sulfoxide.

Inhibition of SARS-CoV-2 Mpro with Vitamin C, L-Arginine and a Vitamin C/L-Arginine Combination

BACKGROUND

Drug resistance is a critical problem in health care that affects therapy outcomes and requires new approaches to drug design. SARS-CoV-2 Mpro mutations are of concern as they can potentially reduce therapeutic efficacy. Viral infections are amongst the many disorders for which nutraceuticals have been employed as an adjunct therapy. The aim of this study was to examine the potential in vitro activity of L-arginine and vitamin C against SARS-CoV-2 Mpro.

METHODS

The Mpro inhibition assay was developed by cloning, expression, purification, and characterization of Mpro. Selected compounds were then screened for protease inhibition.

RESULTS

L-arginine was found to be active against SARS-CoV-2 Mpro, while a vitamin C/L-arginine combination had a synergistic antiviral action against Mpro. These findings confirm the results of our previous in silico repurposing study that showed L-arginine and vitamin C were potential Mpro inhibitors. Moreover, they suggest a possible molecular mechanism to explain the beneficial effect of arginine in COVID patients.

CONCLUSIONS

The findings of the current study are important because they help to identify COVID-19 treatments that are efficient, inexpensive, and have a favorable safety profile. The results of this study also suggest a possible adjuvant nutritional strategy for COVID-19 that could be used in conjunction with pharmacological agents.