Thermodynamics of a Ca2+ dependent, highly thermostable and detergent compatible purified alkaline serine protease from Nocardiopsis xinjiangensis strain OM-6.

Extracellular alkaline protease producing salt tolerant alkaliphilic actinobacteria, Nocardiopsis xinjiangensis strain OM-6 was isolated from Okha Madi (OM) site of coastal Gujarat, India. The purified protease was stable even at 70°C in 100mM Ca2+ with Kd=20×10-3 and t1/2=34min. The activation energies (E), enthalpy (∆H*) and entropy (∆S*) for protease deactivation were 29.35kJ/mol, 26.68kJ/mol and -186.22J/mol, respectively in 200mM Ca2+. The ∆G* for protease deactivation was 97.63kJ/mol at 50°C in 100mM Ca2+. OM-6 protease exhibited enhanced residual activities up to 103%, 70%, 144% and 119% with SDS, CTAB, Tween 80 and Triton X-100, respectively after 2h of incubation at 40°C. Interestingly, residual activity of OM-6 protease increased by 450% and 559% in 50mM H2O2 and 10mM ß-mercaptoethanol respectively even after 2h of incubation. Moreover, protease retained 100% of its original activity with H2O2 and ß-mercaptoethanol at highest concentration after 24h. The protease retained more than 60% of original activity with 1% w/v of each commercial detergent even after 2h at 40°C. These unique properties of protease make it an ideal choice for application in detergent formulations and enzymatic peptide synthesis.

Thermodynamics of a Ca(2+)-dependent highly thermostable alkaline protease from a haloalkliphilic actinomycete.

An alkaline protease from salt-tolerant alkaliphilic actinomycetes, Nocardiopsis alba OK-5 was purified by a single-step hydrophobic interaction chromatography and characterized. The purified protease with an estimated molecular mass of 20 kDa was optimally active at 70 °C in 0-3 M NaCl and 0-100 mM Ca(2+) displaying significant stability at 50-80 °C. The enzyme was stable at 80 °C in 100 mM Ca(2+) with Kd of 17 × 10(-3) and t1/2 of 32 min. The activation energy (Ea), enthalpy (ΔH*), and entropy (ΔS*) for the protease deactivation calculated in the presence of 200 mM Ca(2+) were 38.15 kJ/mol, 35.49 kJ/mol and 183.48 J/mol, respectively. The change in free energy (ΔG*) for protease deactivation at 60 °C in 200 mM Ca(2+) was 95.88 kJ/mol. Decrease in ΔH* reflected reduced cooperativity of deactivation and unfolding. The enzyme was intrinsically stable that counteracted heat denaturation by a weak cooperativity during the unfolding. Further, the enzyme was highly stable in the presence of various cations, surfactants, H2O2, ß-mercaptoethanol, and commercial detergents. The compatibility of the enzyme with various cations, surfactants, and detergent matrices suggests its suitability as an additive in the detergents and peptide synthesis.

Characteristics and thermodynamics of a thermostable protease from a salt-tolerant alkaliphilic actinomycete.

An alkaline serine protease from a newly isolated salt-tolerant alkaliphilic actinomycetes, Brachystreptospora xinjiangensis OM-6 was purified with 35- and 26-fold purification and 47% and 22% yield employing two steps and one step methods, respectively. The enzyme was quite stable at 80 °C in 30% Na-glutamate with the deactivation rate constant (Kd) 8.66 and half life (t1/2) 80.04 min. The activation energies (E), enthalpy (ΔH*), entropy (ΔS*) and change in free energy (ΔG*) for the protease deactivation were calculated in the presence of 30% Na-glutamate and correlated with the enzyme stability. The thermodynamic analysis corresponded the trends of the enzyme stability and inactivation. The enzyme retained high activity and significant stability at higher salt, temperature, range of pH and metal ions. The enzyme was extremely resistant against urea denaturation, oxidizing and reducing agents and surfactants, a finding which is rather unique and restricted to only few proteins.

Cloning and expression of alkaline protease genes from two salt-tolerant alkaliphilic actinomycetes in E. coli.

Cloning and expression of recombinant alkaline serine proteases from two salt tolerant alkaliphilic actinomycetes strains: OM-6 (EU710555.1) and OK-5 (HM560975) were successfully obtained in mesophilic host, Escherichia coli. The positive clones harboring protease genes were selected on the basis of restriction analysis on agarose gel. The effect of temperature and IPTG concentrations on the expression of recombinant proteases and solubilization of the expressed enzymes was assessed. SDS-PAGE revealed protease bands corresponding to 25 kDa and 20 kDa molecular mass representing OM-6 and OK-5 proteases, respectively. Cloning and expression of alkaline proteases from salt tolerant alkaliphilic actinomycetes would pave the way for further biochemical and molecular characterization to achieve unexplored features of the biocatalysts from extremophiles.