A novel neutral protease from Thermoactinomyces species 27a: sequencing of the gene, purification, and characterization of the enzyme

Purification and Characterization of a DegP-Type Protease from the Marine Bacterium Cobetia amphilecti KMM 296

A new member of the DegP-type periplasmic serine endoproteases of the S1C family from the marine bacterium Cobetia amphilecti KMM 296 (CamSP) was expressed in Escherichia coli cells. The calculated molecular weight, number of amino acids, and isoelectric point (pI) of the mature protein CamSP are 69.957 kDa, 666, and 4.84, respectively. The proteolytic activity of the purified recombinant protease CamSP was 2369.4 and 1550.9 U/mg with the use of 1% bovine serum albumin (BSA) and casein as the substrates, respectively. The enzyme CamSP exhibited maximum activity at pH 6.0-6.2, while it was stable over a wide pH range from 5.8 to 8.5. The optimal temperature for the CamSP protease activity was 50 °C. The enzyme required NaCl or KCl at concentrations of 0.3 and 0.5 M, respectively, for its maximum activity. The Michaelis constant (K_m) and V_max for BSA were determined to be 41.7 µg/mL and 0.036 µg/mL min^-1, respectively. The metal ions Zn²⁺, Cu²⁺, Mn²⁺, Li²⁺, Mg²⁺, and Ca²⁺ slightly activated CamSP, while the addition of CoCl₂ to the incubation mixture resulted in a twofold increase in its protease activity. Ethanol, isopropanol, glycerol, and Triton-X-100 increased the activity of CamSP from two- to four-times. The protease CamSP effectively degraded the wheat flour proteins but had no proteolytic activity towards soybean, corn, and the synthetic substrates, α-benzoyl-Arg-p-nitroanilide (BAPNA) and N-Succinyl-L-alanyl-L-alanyl-L-prolyl-L-phenylalanine 4-nitroanilide (SAPNA).

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.

Autocatalytic activation of a thermostable glutamyl endopeptidase capable of hydrolyzing proteins at high temperatures

Glutamyl endopeptidases (GSEs) specifically hydrolyze peptide bonds formed by α-carboxyl groups of Glu and Asp residues. We cloned the gene for a thermophilic GSE (designated TS-GSE) from Thermoactinomyces sp. CDF. A proform of TS-GSE that contained a 61-amino acid N-terminal propeptide and a 218-amino acid mature domain was produced in Escherichia coli. We found that the proform possessed two processing sites and was capable of autocatalytic activation via multiple pathways. The N-terminal propeptide could be autoprocessed at the Glu^-1-Ser¹ bond to directly generate the mature enzyme. It could also be autoprocessed at the Glu^-12-Lys^-11 bond to yield an intermediate, which was then converted into the mature form after removal of the remaining part of the propeptide. The segment surrounding the two processing sites was flexible, which allowed the proform and the intermediate form to be trans-processed into the mature form by either active TS-GSE or heterogeneous proteases. Deletion analysis revealed that the N-terminal propeptide is important for the correct folding and maturation of TS-GSE. The propeptide, even its last 11-amino acid peptide segment, could inhibit the activity of its cognate mature domain. The mature TS-GSE displayed a temperature optimum of 85 °C and retained approximately 90 % of its original activity after incubation at 70 °C for 6 h, representing the most thermostable GSE reported to date. Mutational analysis suggested that the disulfide bonds Cys³²-Cys⁴⁸ and Cys¹⁸⁰-Cys¹⁸³ cumulatively contributed to the thermostability of TS-GSE.

Propeptides as modulators of functional activity of proteases

Most proteases are synthesized in the cell as precursor-containing propeptides. These structural elements can determine the folding of the cognate protein, function as an inhibitor/activator peptide, mediate enzyme sorting, and mediate the protease interaction with other molecules and supramolecular structures. The data presented in this review demonstrate modulatory activity of propeptides irrespective of the specific mechanism of action. Changes in propeptide structure, sometimes minor, can crucially alter protein function in the living organism. Modulatory activity coupled with high variation allows us to consider propeptides as specific evolutionary modules that can transform biological properties of proteases without significant changes in the highly conserved catalytic domains. As the considered properties of propeptides are not unique to proteases, propeptide-mediated evolution seems to be a universal biological mechanism.

Degradation of intact chicken feathers by Thermoactinomyces sp. CDF and characterization of its keratinolytic protease

Thermoactinomyces is known for its resistance to extreme environmental conditions and its ability to digest a wide range of hard-to-degrade compounds. Here, Thermoactinomyces sp. strain CDF isolated from soil was found to completely degrade intact chicken feathers at 55 °C, with the resulting degradation products sufficient to support growth as the primary source of both carbon and nitrogen. Although feathers were not essential for the expression of keratinase, the use of this substrate led to a further 50-300 % increase in enzyme production level under different nutrition conditions, with extracellular keratinolytic activity reaching its highest level (∼400 U/mL) during the late-log phase. Full degradation of feathers required the presence of living cells, which are thought to supply reducing agents necessary for the cleavage of keratin disulfide bonds. Direct contact between the hyphae and substrate may enhance the reducing power and protease concentrations present in the local microenvironment, thereby facilitating keratin degradation. The gene encoding the major keratinolytic protease (protease C2) of strain CDF was cloned, revealing an amino acid sequence identical to that of subtilisin-like E79 protease from Thermoactinomyces sp. E79, albeit with significant differences in the upstream flanking region. Exogenous expression of protease C2 in Escherichia coli resulted in the production of inclusion bodies with proteolytic activity, which could be solubilized to an alkaline solution to produce mature protease C2. Purified protease C2 was able to efficiently hydrolyze α- and β-keratins at 60-80 °C and pH 11.0, representing a promising candidate for enzymatic processing of hard-to-degrade proteins such as keratinous wastes.

Enzymatic characteristics of a recombinant neutral protease I (rNpI) from Aspergillus oryzae expressed in Pichia pastoris

A truncated neutral protease I (NpI) from Aspergillus oryzae 3.042 was expressed in Pichia pastoris with a high enzyme yield of 43101 U/mL. Its optimum pH was about 8.0, and it was stable in the pH range of 5.0-9.0. Its optimum temperature was about 55 °C and retained >90% activity at 50 °C for 120 min. Recombinant NpI (rNpI) was inhibited by Cu(2+) and EDTA. Eight cleavage sites of rNpI in oxidized insulin B-chain were determined by mass spectrometry, and five of them had high hydrophobic amino acid affinity, which makes it efficient in producing antihypertensive peptide IPP from β-casein and a potential debittering agent. The high degree of hydrolysis (DH) of rNpI to soybean protein (8.8%) and peanut protein (11.1%) compared to papain and alcalase makes it a good candidate in the processing of oil industry byproducts. The mutagenesis of H(429), H(433), and E(453) in the deduced zinc-binding motif confirmed rNpI as a gluzincin. All of these results show the great potential of rNpI to be used in the protein hydrolysis industry.

Cloning, sequencing, expression, and characterization of protealysin, a novel neutral proteinase from Serratia proteamaculans representing a new group of thermolysin-like proteases with short N-terminal region of precursor

The gene of Serratia proteamaculans proteinase, protealysin, was cloned, sequenced, and expressed in Escherichia coli. The gene encoded a precursor of 341 amino acids (AAs) with a significant homology to thermolysin-like proteinases (TLPs). The molecular weight of the purified mature active recombinant protein was 32 kDa, the N-terminal amino acid sequence was AKTSTGGEVI. The optimum pH for azocasein hydrolysis by protealysin was seven and it was completely inhibited by o-phenanthroline. The enzyme hydrolyzed 3-(2-furyl)acryloyl-glycyl-L-leucine amide, the standard substrate for TLPs, with k(cat)/K(m) ratio of (2.52 +/- 0.02) x 10(2) M(-1) s(-1). Protealysin maturation removes 50 AA from the N-terminus of the precursor. The removed region had no similarity with the preprosequence of thermolysin (232 AA) but was homologous to some other TLPs. These proteins shared a conserved 7-AA motif near the initial methionine. Such motif was also found in some nonproteolytic putative proteins; two of them were eukaryotic.