MERS-CoV papain-like protease (PL^pro): expression, purification, and spectroscopic/thermodynamic characterization

Within a decade, MERS-CoV emerged with nearly four times higher case fatality rate than an earlier outbreak of SARS-CoV and spread out in 27 countries in short span of time. As an emerging virus, combating it requires an in-depth understanding of its molecular machinery. Therefore, conformational characterization studies of coronavirus proteins are necessary to advance our knowledge of the matter for the development of antiviral therapies. In this study, MERS-CoV papain-like protease (PL^pro) was recombinantly expressed and purified. Thermal folding pathway and thermodynamic properties were characterized using dynamic multimode spectroscopy (DMS) and thermal shift assay. DMS study showed that the PL^pro undergoes a single thermal transition and follows a pathway of two-state folding with T _m and van't Hoff enthalpy values of 54.4 ± 0.1 °C and 317.1 ± 3.9 kJ/mol, respectively. An orthogonal technique based on intrinsic tryptophan fluorescence also showed that MERS-CoV PL^pro undergoes a single thermal transition and unfolds via a pathway of two-state folding with a T _m value of 51.4 °C. Our findings provide significant understandings of the thermodynamic and structural properties of MERS-CoV PL^pro.