Biochemical and molecular characterization of a thermo- and detergent-stable alkaline serine keratinolytic protease from Bacillus circulans strain DZ100 for detergent formulations and feather-biodegradation process

An extracellular keratinolytic protease (SAPDZ) was produced and purified from a newly isolated Bacillus circulans strain DZ100. Matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF/MS) analysis revealed that the purified enzyme is a monomer with a molecular mass of 32019.10 Da. The sequence of the 25 N-terminal residues of SAPDZ showed high homology with those of Bacillus proteases. Optimal activity was achieved at pH 12.5 and 85 °C. This enzyme was completely inhibited by phenylmethanesulfonyl fluoride (PMSF) and diiodopropyl fluorophosphates (DFP), which suggests that it belongs to the serine protease family. Compared to the other tested proteases, SAPDZ exhibited broader substrate specificity, higher levels of catalytic efficiency, and greater keratinolytic activity, which made it able to accomplish the entire feather-biodegradation process on its own. The sapDZ gene encoding SAPDZ was cloned, sequenced, and expressed in Escherichia coli. The biochemical properties exhibited by the extracellular purified recombinant enzyme (rSAPDZ) were similar to those of the native one. Above all, SAPDZ exhibited marked stability to detergents, making it a potential candidate for future applications in detergent formulations and an efficient eco-friendly enzyme for the biodegradation of feather keratin.