Two steps purification, biochemical characterization, thermodynamics and structure elucidation of thermostable alkaline serine protease from Nocardiopsis alba strain OM-5

The Nocardiopsis alba strain OM-5 showed maximum protease production in submerged culture. The OM-5 protease was purified by hydrophobic interaction chromatography. The purified protease of 68 kDa showed maximum activity (3312 ± 1.64 U/mL) at 70 °C and was quite stable at 80 °C up to 4 M NaCl (w/v) at pH 9. The purified protease showed significant activity and stability in different cations, denaturing agents, metal ions, and osmolytes. The thermodynamic parameters including deactivation rate constant (Kd) and half lives (t1/2) at 50–80 °C were in the range of 2.50 × 10−3 to 5.50 × 10−3 and 277.25–111.25 min respectively at 0–4 M NaCl. The structural stability of the OM-5 protease under various harsh conditions was elucidated by circular dichroism (CD) spectroscopy followed by K2D3 analysis revealed that the native structure of OM-5 protease was stable even in sodium dodecyl sulfate and Tween 20 indicated by increased α-helices content assisted with decreased β-sheets content. •Biocatalytic potential of the haloalkaliphilic marine actinomycete•Submerged cultivation and cost-effective purification of alkaline serine protease•Probing protein folding of the enzyme at high temperature and in strong denaturants•Thermodynamic parameters indicated stability of protease in salt/high temperature.•Circular dichroism spectra analysis revealed structural stability of the enzyme.•Oxidants, cations, anions, metal ions, osmolytes, and surfactant stable protease