Stability of Alkaline Proteases from Haloalkaliphilic Actinobacteria Probed by Circular Dichroism Spectroscopy

Abstract

Two halo-tolerant and alkaliphilic actinomycetes, Nocardiopsis alba OM-4 (GeneBank Number, KC119568) and Nocardiopsis alba TATA-13 (GeneBank Number, KC119569) isolated from the salt-enriched soil of the Coastal Gujarat (India) were studied for their proteases. The low molecular weight (19–20 kDa) alkaline proteases were purified by the hydrophobic interaction chromatography on Phenyl Sepharose 6 FF column. The enzymes were optimally active at 60–70°C and pH 10.0. NaCl enhanced the catalysis and enzyme stability at different temperatures and in the presence of up to 50% concentrations of various solvents. The purified enzymes were resistant against various surfactants and inhibitors, suggesting their potential applications in the detergent industry. The changes in the secondary structures were probed by the circular dichroism spectroscopy at various temperatures and solvents, followed by the K2D analysis. With increasing temperatures, the contents of the α- helices and β-sheets increased in the N. alba OM-4 protease, while a reverse trend was evident for the N. alba TATA-13 protease. On the other hand, the α-helix contents increased accompanied with decreased β-sheets in both proteases in the presence of different solvents.