A novel keratinase from Bacillus tequilensis strain Q7 with promising potential for the leather bating process.

The present paper reports on the purification and characterization of an extracellular keratinase (KERQ7) newly purified from Bacillus tequilensis Q7. Pure protein was obtained after ammonium sulfate fractionation (30-60%), followed by Mono S Sepharose cation-exchange chromatography. MALDI-TOF/MS analysis revealed that the purified enzyme was a monomer with a molecular mass of 28,355.07-Da. The sequence of the 21 N-terminal residues of KERQ7 showed high homology with those of Bacillus keratinases. Optimal activity was achieved at pH 7 and 30°C. KERQ7 was completely inhibited by PMSF and DFP, which suggests that it belongs to the serine keratinase family. KERQ7 displayed higher levels of hydrolysis and catalytic efficiency than Basozym(®) CS 10, Koropon(®) SC 5K, and Pyrase(®) 250 MP. The kerQ7 gene encoding KERQ7 was cloned, sequenced, and expressed in Escherichia coli BL21(DE3)pLysS. The biochemical properties of the extracellular purified recombinant enzyme (rKERQ7) were similar to those of native KERQ7. The deduced amino acid sequence showed strong homology with other Bacillus keratinases. The highest sequence identity value (97%) was obtained with KERUS from Brevibacillus brevis US575, with only 7 aa of difference. These properties make KERQ7 a potential promising and eco-friendly enzymatically enhanced process for animal hide bating in the leather processing industry.

Probing the crucial role of Leu31 and Thr33 of the Bacillus pumilus CBS alkaline protease in substrate recognition and enzymatic depilation of animal hide.

The sapB gene, encoding Bacillus pumilus CBS protease, and seven mutated genes (sapB-L31I, sapB-T33S, sapB-N99Y, sapB-L31I/T33S, sapB-L31I/N99Y, sapB-T33S/N99Y, and sapB-L31I/T33S/N99Y) were overexpressed in protease-deficient Bacillus subtilis DB430 and purified to homogeneity. SAPB-N99Y and rSAPB displayed the highest levels of keratinolytic activity, hydrolysis efficiency, and enzymatic depilation. Interestingly, and at the semi-industrial scale, rSAPB efficiently removed the hair of goat hides within a short time interval of 8 h, thus offering a promising opportunity for the attainment of a lime and sulphide-free depilation process. The efficacy of the process was supported by submitting depilated pelts and dyed crusts to scanning electron microscopic analysis, and the results showed well opened fibre bundles and no apparent damage to the collagen layer. The findings also revealed better physico-chemical properties and less effluent loads, which further confirmed the potential candidacy of the rSAPB enzyme for application in the leather industry to attain an ecofriendly process of animal hide depilation. More interestingly, the findings on the substrate specificity and kinetic properties of the enzyme using the synthetic peptide para-nitroanilide revealed strong preferences for an aliphatic amino-acid (valine) at position P1 for keratinases and an aromatic amino-acid (phenylalanine) at positions P1/P4 for subtilisins. Molecular modeling suggested the potential involvement of a Leu31 residue in a network of hydrophobic interactions, which could have shaped the S4 substrate binding site. The latter could be enlarged by mutating L31I, fitting more easily in position P4 than a phenylalanine residue. The molecular modeling of SAPB-T33S showed a potential S2 subside widening by a T33S mutation, thus suggesting its importance in substrate specificity.