Identification and homology modeling of a new biotechnologically compatible serine alkaline protease from moderately halotolerant Gracilibacillus boraciitolerans strain LO15

A new serine alkaline protease (designated as SAPGB) from Gracilibacillus boraciitolerans strain LO15, was produced (9000 U/mL), purified, and characterized. SAPGB has a monomer structure with a precise molecular weight of 30,285.03 kDa as learnt from matrix-assisted laser desorption/ionization-time of flight/mass spectroscopy (MALDI-TOF/MS) exploration. The NH2-terminal amino-acid succession revealed significant identity with Bacillus proteases. The SAPGB was irreversibly inhibited by diiodopropyl fluorophosphates (DFP) and phenylmethylsulfonyl fluoride (PMSF). The enzyme displayed optimum activity at 65 °C and pH 10. The maximal activity was achieved in the range 0.5–5 M NaCl and about 52% of the activity was preserved across the broad salinity range of 0–30%. SAPGB exhibited a considerable catalytic efficiency (ratio kcat/Km) and degree of hydrolysis (DH). In addition, SAPGB showed a high tolerance to several organic solvents and an excellent detergent compatibility than SAPV, SAPA, Thermolysin type X, and Esperase 8.0 L. These properties make SAPGB a potential candidate for detergent formulations. On the other hand, sapGB gene was cloned and expressed in E. coli BL21(DE3)pLysS and the biochemical properties of the purified extracellular recombinant protease (rSAPGB) were similar to those of SAPGB. Finally, a 3D structural model of SAPGB was constructed by homology modeling. [Display omitted] •The protease SAPGB from Gracilibacillus boraciitolerans strain LO15 was purified and typified.•The optimum pH and temperature values for activity were pH 10 and 65 °C, respectively.•The sapGB gene encoding SAPGB, was cloned, sequenced, and expressed in E. coli BL21(DE3)pLysS.•Pro-SAPGB 3D-structure model was built using structure of Pro-subtilisin E (PDB ID: 3WHI).•The SAPGB enzyme is a potential candidate for peptide synthesis and detergent formulations.