Expression, purification, and biophysical characterization of recombinant MERS-CoV main (M) protease.

MERS-CoV main protease (M) is essential for the maturation of the coronavirus; therefore, considered a potential drug target. Detailed conformational information is essential to developing antiviral therapeutics. However, the conformation of MERS-CoV M under different conditions is poorly characterized. In this study, MERS-CoV M was recombinantly produced in E.coli and characterized its structural stability with respect to changes in pH and temperatures. The intrinsic and extrinsic fluorescence measurements revealed that MERS-CoV M tertiary structure was exposed to the polar environment due to the unfolding of the tertiary structure. However, the secondary structure of MERS-CoV M was gained at low pH because of charge-charge repulsion. Furthermore, differential scanning fluorometry studies of M showed a single thermal transition at all pHs except at pH 2.0; no transitions were observed. The data from the spectroscopic studies suggest that the MERS-CoV M forms a molten globule-like state at pH 2.0. Insilico studies showed that the covid-19 M shows 96.08% and 50.65% similarity to that of SARS-CoV M and MERS-CoV M, respectively. This study provides a basic understanding of the thermodynamic and structural properties of MERS-CoV M.