Biochemical and molecular characterization of a detergent-stable serine alkaline protease from Bacillus pumilus CBS with high catalytic efficiency

We have described previously the potential use of an alkaline protease from Bacillus pumilus CBS as an effective additive in laundry detergent formulations [B. Jaouadi, S. Ellouz-Chaabouni, M. Ben Ali, E. Ben Messaoud, B. Naili, A. Dhouib, S. Bejar, A novel alkaline protease from Bacillus pumilus CBS having a high compatibility with laundry detergent and a high feather-degrading activity, Process Biochem, submitted for publication]. Here, we purified this enzyme (named SAPB) and we cloned, sequenced and over-expressed the corresponding gene. The enzyme was purified to homogeneity using salt precipitation and gel filtration HPLC. The pure protease was found to be monomeric protein with a molecular mass of 34598.19 Da as determined by MALDI-TOF mass spectrometry. The NH2-terminal sequence of first 21 amino acids (aa) of the purified SAPB was AQTVPYGIPQIKAPAVHAQGY and was completely identical to proteases from other Bacillus pumilus species. This protease is strongly inhibited by PMSF and DFP, showing that it belongs to the serine proteases superfamily. Interestingly, the optimum pH is 10.6 while the optimum temperature was determined to be 65 °C. The enzyme was completely stable within a wide range of pH (7.0–10.6) and temperature (30–55 °C). One of the distinguishing properties is its catalytic efficiency (kcat/Km) calculated to be 45,265 min−1 mM−1 and 147,000 min−1 mM−1 using casein and AAPF as substrates, respectively, which is higher than that of Subtilisin Carlsberg, Subtilisin BPN′ and Subtilisin 309 determined under the same conditions. In addition, SAPB showed remarkable stability, for 24 h at 40 °C, in the presence of 5% Tween-80, 1% SDS, 15% urea and 10% H2O2, which comprise the common bleach-based detergent formulation. The sapB gene encoding SAPB was cloned, sequenced and over-expressed in Escherichia coli. The purified recombinant enzyme (rSAPB) has the same physicochemical and kinetic properties as the native one. SapB gene had an ORF of 1149 bp encoding a protein of 383 aa organized into a signal peptide (29 aa), a pro-protein (79 aa) and a mature enzyme (275 aa). The deduced amino acid sequence inspection displays an important homology with other bacterial proteases. The highest homology of 98.1% was found with BPP-A protease from Bacillus pumilus MS-1, with only 8 aa of difference.