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

Directed evolution driving the generation of an efficient keratinase variant to facilitate the feather degradation

Keratinases can specifically degrade keratins, which widely exist in hair, horns, claws and human skin. There is a great interest in developing keratinase to manage keratin waste generated by the poultry industry and reusing keratin products in agriculture, medical treatment and feed industries. Degradation of keratin waste by keratinase is more environmentally friendly and more sustainable compared with chemical and physical methods. However, the wild-type keratinase-producing strains usually cannot meet the requirements of industrial production, and some are pathogenic, limiting their development and utilization. The main purpose of this study is to improve the catalytic performance of keratinase via directed evolution technology for the degradation of feathers. We first constructed a mutant library through error-prone PCR and screened variants with enhanced enzyme activity. The keratinase activity was further improved through fermentation conditions optimization and fed-batch strategies in a 7-L bioreactor. As a result, nine mutants with enhanced activity were identified and the highest enzyme activity was improved from 1150 to 8448 U/mL finally. The mutant achieved efficient biodegradation of feathers, increasing the degradation rate from 49 to 88%. Moreover, a large number of amino acids and soluble peptides were obtained as degradation products, which were excellent protein resources to feed. Therefore, the study provided a keratinase mutant with application potential in the management of feather waste and preparation of protein feed additive.

Production of subtilisin proteases in bacteria and yeast

In this review, we discuss the progress in the study and modification of subtilisin proteases. Despite longstanding applications of microbial proteases and a large number of research papers, the search for new protease genes, the construction of producer strains, and the development of methods for their practical application are still relevant and important, judging by the number of citations of the research articles on proteases and their microbial producers. This enzyme class represents the largest share of the industrial production of proteins worldwide. This situation can explain the high level of interest in these enzymes and points to the high importance of designing domestic technologies for their manufacture. The review covers subtilisin classification, the history of their discovery, and subsequent research on the optimization of their properties. An overview of the classes of subtilisin proteases and related enzymes is provided too. There is a discussion about the problems with the search for (and selection of) subtilases from natural strains of various microorganisms, approaches to (and specifics of) their modification, as well as the relevant genetic engineering techniques. Details are provided on the methods for expression optimization of industrial subtilases of various strains: the details of the most important parameters of cultivation, i.e., composition of the media, culture duration, and the influence of temperature and pH. Also presented are the results of the latest studies on cultivation techniques: submerged and solid-state fermentation. From the literature data reviewed, we can conclude that native enzymes (i.e., those obtained from natural sources) currently hardly have any practical applications because of the decisive advantages of the enzymes modified by genetic engineering and having better properties: e.g., thermal stability, general resistance to detergents and specific resistance to various oxidants, high activity in various temperature ranges, independence from metal ions, and stability in the absence of calcium. The vast majority of subtilisin proteases are expressed in producer strains belonging to different species of the genus Bacillus. Meanwhile, there is an effort to adapt the expression of these enzymes to other microbes, in particular species of the yeast Pichia pastoris.

Heterologous expression and purification of keratinase from Actinomadura viridilutea DZ50: feather biodegradation and animal hide dehairing bioprocesses

The keratin-degrading bacterium Actinomadura viridilutea DZ50 secretes a keratinase (KERDZ) with potential industrial interest. Here, the kerDZ gene was extracellularly expressed in Escherichia coli BL21(DE3)pLysS using pTrc99A vector. The recombinant enzyme (rKERDZ) was purified and biochemically characterized. Results showed that the native and recombinant keratinases have similar biochemical characteristics. The conventional dehairing with lime and sodium sulfide degrades the hair to the extent that it cannot be recovered. Thus, these chemical processes become a major contributor to wastewater problem and create a lot of environmental concern. The complete dehairing was achieved with 2000 U/mL rKERDZ for 10 h at 40 °C. In fact, keratinase assisted dehairing entirely degraded chicken feather (45 mg) and removed wool/hair from rabbit, sheep, goat, or bovine' hides (1.6 kg) while preserving the collagen structure. The enzymatic process is the eco-friendly option that reduces biological (BOD) (50%) and chemical (COD) oxygen demands (60%) in leather processing. Consequently, the enzymatic hair removal process could solve the problem of post-treatments encountering the traditional leather processing. The enzymatic (rKERDZ) dehaired leather was analyzed by scanning electron microscopic (SEM) studies, which revealed similar fiber orientation and compactness compared with control sample. Those properties support that the rKERDZ enzyme-mediated process is greener to some extent than the traditional one.

Extracellular Production, Characterization, and Engineering of a Polyextremotolerant Subtilisin-Like Protease From Feather-Degrading Thermoactinomyces vulgaris Strain CDF

Here, the gene encoding a subtilisin-like protease (protease Als) was cloned from Thermoactinomyces vulgaris strain CDF and expressed in Escherichia coli. The recombinant enzyme was released into the culture medium of E. coli as a mature form (mAls). Purified mAls displayed optimal activity at 60–70°C and pH 10.0 using azo-casein as the substrate, and showed a half-life of 13.8 h at 70°C. Moreover, the activity of thermostable mAls was comparable to or higher than those of mesophilic subtilisin Carlsberg and proteinase K at low temperatures (10–30°C). Protease Als was also stable in several organic solvents and showed high compatibility with commercial laundry detergents. Notably, mAls exhibited approximately 100% of its activity at 3 M NaCl, and showed enhanced thermostability with the increase of NaCl concentration up to 3 M. Protease Als possesses an excess of solvent-accessible acidic amino acid residues, which may account for the high halotolerance of the enzyme. Compared with homologous protease C2 from the same strain, protease Als exhibits substantially lower activity toward insoluble keratin substrates but efficiently hydrolyzes soluble keratin released from chicken feathers. Additionally, direct substitution of the substrate-binding site of protease Als with that of protease C2 improves its activity against insoluble keratin substrates. By virtue of its polyextremotolerant attribute and kerationolytic capacity, protease Als may find broad applications in various industries such as laundry detergents, food processing, non-aqueous biocatalysis, and feather processing.

Proteolytic extracts of three Bromeliaceae species as eco-compatible tools for leather industry

Most tanneries use high proportions of Na₂S and CaO during the dehairing step, resulting in effluents of high alkalinity and large amounts of suspended solid, besides the risk of liberating the toxic H₂S. Solid waste rich in protein is another environmental problem of tanneries. Enzymes are an interesting technological tool for industry due to their biodegradability, nontoxic nature, and nonpolluting effluent generation. In the leather industry, proteases have been chosen as a promising eco-friendly alternative to Na₂S/CaO dehairing. Extracts with high proteolytic activity have been obtained from fruits of Bromeliaceae species: Bromelia balansae Mez (Bb), Bromelia hieronymi Mez (Bh), and Pseudananas macrodontes (Morr.) Harms (Pm). In this work, Bb, Bh, and Pm have been studied for application in the leather industry, focusing in their dehairing properties. Enzymatic activities were measured against collagen, keratin, elastin, and epidermis while a dehairing assay was performed by employing cowhide. All extracts showed similar activity on collagen and epidermis, while Bh and Pm were the most active against keratin at the same caseinolytic unit (CU) values; Bh was the only extract active against elastin. Bb (1 CU/ml), Bh (1.5 CU/ml), and Pm (0.5 CU/ml) were able to depilate cowhide. Desirable characteristics of dehairing were observed for all extracts since hair pores did not show residual hair, grain surface was clean and intact, and collagen fiber bundles of dermis were not damaged. In conclusion, results here presented show that proteolytic extracts of Bromeliaceae species are promising eco-compatible tools for leather industry.

Biochemical and molecular characterization of new keratinoytic protease from Actinomadura viridilutea DZ50

A new extracellular thermostable keratinolytic protease, designated KERDZ, was purified and characterized from a thermophilic actinomycetes Actinomadura viridilutea DZ50 isolated from Algerian fishing port. The isolate exhibited high keratinase production when grown in chicken-feather meal media (18,000U/ml) after 96-h of incubation at 45°C. The enzyme was purified by ammonium sulfate precipitation (35-55%)-dialysis and heat treatment (30min at 75°C) followed by UNO S-1 FPLC cation exchange chromatography and size exclusion HPLC column. The biochemical characterizations carried on include physico-chemical determination and spectroscopic analysis. The MALDI-TOF/MS analysis revealed that the purified enzyme was a monomer with a molecular mass of 19536.10-Da. The sequence of the 25 N-terminal residues of KERDZ showed high homology with those of actinomycetes keratinases. Optimal activity was achieved at pH 11 and 80°C. KERDZ was completely inhibited by PMSF and DFP suggested its belonging to the serine keratinase family. KERDZ displayed higher levels of hydrolysis and catalytic efficiency than bacterial keratinases (KERAK-29, Actinase E, and KERAB) and subtilisins (subtilisin Carlsberg and subtilisin Novo). The kerDZ gene encoding KERDZ was isolated and its DNA sequence was determined. These properties make KERDZ a potential, promising and eco-friendly alternative to the conventional chemicals used for industrial applications.

A novel organic solvent- and detergent-stable serine alkaline protease from Trametes cingulata strain CTM10101

A protease-producing fungus was isolated from an alkaline wastewater of chemical industries and identified as Trametes cingulata strain CTM10101 on the basis of the ITS rDNA gene-sequencing. It was observed that the fungus strongly produce extracellular protease grown at 30°C in potato-dextrose-broth (PDB) optimized media (13500U/ml). The pure serine protease isolated by Trametes cingulata (designated SPTC) was purified by ammonium sulfate precipitation-dialysis followed by heat-treatment and UNO S-1 FPLC cation-exchange chromatography. The chemical characterization carried on include phisico-chemical determination and spectroscopie analysis. The MALDI-TOF/MS analysis revealed that the purified enzyme was a monomer with a molecular mass of 31405.16-Da. The enzyme had an NH2-terminal sequence of ALTTQTEAPWALGTVSHKGQAST, thus sharing high homology with those of fungal-proteases. The optimum pH and temperature values of its proteolytic activity were pH 9 and 60°C, respectively, and its half-life times at 60 and 70°C were 9 and 5-h, respectively. It was completely inhibited by PMSF and DFP, which strongly suggested its belonging to the serine protease family. Compared to Flavourzyme(®)500L from Aspergillus oryzae and Thermolysin typeX from Geobacillus stearothermophilus, SPTC displayed higher levels of hydrolysis, substrate specificity, and catalytic efficiency as well as elevated organic solvent tolerance and considerable detergent stability. Finally, SPTC could potentially be used in peptide synthesis and detergent formulations.

Construction of a Rapid Feather-Degrading Bacterium by Overexpression of a Highly Efficient Alkaline Keratinase in Its Parent Strain Bacillus amyloliquefaciens K11

Keratinase is essential to degrade the main feather component, keratin, and is of importance for wide industrial applications. In this study, Bacillus amyloliquefaciens strain K11 was found to have significant feather-degrading capacity (completely degraded whole feathers within 24 h). The keratinase encoding gene, kerK, was expressed in Bacillus subtilis SCK6. The purified recombinant KerK showed optimal activity at 50 °C and pH 11.0 and degraded whole feathers within 0.5 h in the presence of DTT. The recombinant plasmids harboring kerK were extracted from B. subtilis SCK6 and transformed into B. amyloliquefaciens K11. As a result, the recombinant B. amyloliquefaciens K11 exhibited enhanced feather-degrading capacity with shortened reaction time within 12 h and increased keratinolytic activity (1500 U/mL) by 6-fold. This efficient and rapid feather-degrading character makes the recombinant strain of B. amyloliquefaciens K11 have potential for applications in feather meal preparation and waste feather disposal.

Purification and biochemical characterization of two detergent-stable serine alkaline proteases from Streptomyces sp. strain AH4

Streptomyces sp. strain AH4 exhibited a high ability to produce two extracellular proteases when cultured on a yeast malt-extract (ISP2)-casein-based medium. Pure proteins were obtained after heat treatment (30 min at 70 °C) and ammonium sulphate fractionation (30-60 %), followed by size exclusion HPLC column. Matrix assisted laser desorption ionization-time of flight mass spectrometry analysis revealed that the purified enzymes (named SAPS-P1 and SAPS-P2) were monomers with molecular masses of 36,417.13 and 21,099.10 Da, respectively. Their identified N-terminal amino acid displayed high homologies with those of Streptomyces proteases. While SAPS-P1 was optimally active at pH 12.0 and 70 °C, SAPS-P2 showed optimum activity at pH 10.0 and 60 °C. Both enzymes were completely stable within a wide range of temperature (45-75 °C) and pH (8.0-11.5). They were noted to be completely inhibited by phenylmethanesulfonyl fluoride and diisopropyl fluorophosphates, which confirmed their belonging to the serine proteases family. Compared to SAPS-P2, SAPS-P1 showed high thermostability and excellent stability towards bleaching, denaturing, and oxidizing agents. Both enzymes displayed marked stability and compatibility with a wide range of commercial laundry detergents and significant catalytic efficiencies compared to Subtilisin Carlsberg and Protease SG-XIV. Overall, the results indicated that SAPS-P1 and SAPS-P2 can be considered as potential promising candidates for future application as bioadditives in detergent formulations.

Single amino acid mutation alters thermostability of the alkaline protease from Bacillus pumilus: thermodynamics and temperature dependence

Dehairing alkaline protease (DHAP) from Bacillus pumilus BA06 has been demonstrated to have high catalytic efficiency and good thermostability, with potential application in leather processing. In order to get insights into its catalytic mechanism, two mutants with single amino acid substitution according to the homology modeling and multiple sequence alignment were characterized in thermodynamics of thermal denaturation and temperature dependence of substrate hydrolysis. The results showed that both mutants of V149I and R249E have a systematic increase in catalytic efficiency (kcat/Km) in a wide range of temperatures, mainly due to an increase of k1 (substrate diffusion) and k2 (acylation) for V149I and of k2 and k3 (deacylation) for R249E. In comparison with the wild-type DHAP, the thermostability is increased for V149I and decreased for R249E. Thermodynamic analysis indicated that the free energy (ΔGa°) of activation for thermal denaturation may govern the thermostability. The value of ΔGa° is increased for V149I and decreased for R249E. Based on these data and the structural modeling, it is suggested that substitution of Val149 with Ile may disturb the local flexibility in the substrate-binding pocket, leading to enhancement of binding affinity for the substrate. In contrast, substitution of Arg249 with Glu leads to interruption of interaction with the C-terminal of enzyme, thus resulting in less thermostability. This study indicates that amino acid residues in the active center or in the substrate-binding pocket may disturb the catalytic process and can be selected as the target for protein engineering in the bacterial alkaline proteases.