Purification and characterization of organic solvent-stable protease from organic solvent-tolerant Pseudomonas aeruginosa PST-01

A novel salt- and organic solvent-tolerant phosphite dehydrogenase from Cyanothece sp. ATCC 51142

Phosphite dehydrogenase (PtxD) is a promising enzyme for NAD(P)H regeneration. To expand the usability of PtxD, we cloned, expressed, and analyzed PtxD from the marine cyanobacterium Cyanothece sp. ATCC 51142 (Ct-PtxD). Ct-PtxD exhibited maximum activity at pH 9.0°C and 50°C and high stability over a wide pH range of 6.0-10.0. Compared to previously reported PtxDs, Ct-PtxD showed increased resistance to salt ions such as Na+, K+, and NH4 +. It also exhibited high tolerance to organic solvents such as ethanol, dimethylformamide, and methanol when bound to its preferred cofactor, NAD+. Remarkably, these organic solvents enhanced the Ct-PtxD activity while inhibiting the PtxD activity of Ralstonia sp. 4506 (Rs-PtxD) at concentrations ranging from 10% to 30%. Molecular electrostatic potential analysis showed that the NAD+-binding site of Ct-PtxD was rich in positively charged residues, which may attract the negatively charged pyrophosphate group of NAD+ under high-salt conditions. Amino acid composition analysis revealed that Ct-PtxD contained fewer hydrophobic amino acids than other PtxD enzymes, which reduced the hydrophobicity and increased the hydration of protein surface under low water activity. We also demonstrated that the NADH regeneration system using Ct-PtxD is useful for the coupled chiral conversion of trimethylpyruvic acid into L-tert-leucine using leucine dehydrogenase under high ammonium conditions, which is less supported by the Rs-PtxD enzyme. These results imply that Ct-PtxD might be a potential candidate for NAD(P)H regeneration in industrial applications under the reaction conditions containing salt and organic solvent.

What do we learn from enzyme behaviors in organic solvents? - Structural functionalization of ionic liquids for enzyme activation and stabilization

Enzyme activity in nonaqueous media (e.g. conventional organic solvents) is typically lower than in water by several orders of magnitude. There is a rising interest of developing new nonaqueous solvent systems that are more "water-like" and more biocompatible. Therefore, we need to learn from the current state of nonaqueous biocatalysis to overcome its bottleneck and provide guidance for new solvent design. This review firstly focuses on the discussion of how organic solvent properties (such as polarity and hydrophobicity) influence the enzyme activity and stability, and how these properties impact the enzyme's conformation and dynamics. While hydrophobic organic solvents usually lead to the maintenance of enzyme activity, solvents carrying functional groups like hydroxys and ethers (including crown ethers and cyclodextrins) can lead to enzyme activation. Ionic liquids (ILs) are designable solvents that can conveniently incorporate these functional groups. Therefore, we systematically survey these ether- and/or hydroxy-functionalized ILs, and find most of them are highly compatible with enzymes leading to high activity and stability. In particular, ILs carrying both ether and tert-alcohol groups are among the most enzyme-activating solvents. Future direction is to learn from enzyme behaviors in both water and nonaqueous media to design biocompatible "water-like" solvents.

Expression and characterization of a novel organic solvent tolerant protease from Bacillus sphaericus DS11

Organic solvent-tolerant proteases have many applications in the synthesis of peptides. In this study, we have developed a low-cost and convenient method to produce highly concentrated organic solvent-tolerant protease. Organic solvent tolerant protease (OSP) gene from Bacillus sphaericus DS11 was cloned and expressed in Bacillus subtilis WB800. The optimum pH of the recombinant protease was 9.0. The optimum temperature of the recombinant protease was 40 °C. The recombinant protease was purified by ethanol with the yield of (87.33%). The yield of OSP enriched by ethanol was higher than that of by Ni-chelating affinity chromatography, which indicated that precipitation of the recombinant OSP with ethanol is a relatively low-cost and fast method for organic solvent -tolerant protease preparation. These results showed that this enzyme could be very useful in different industrial applications.

Pseudomonas aeruginosa Keratitis: Protease IV and PASP as Corneal Virulence Mediators

Pseudomonas aeruginosa is a leading cause of bacterial keratitis, especially in users of contact lenses. These infections are characterized by extensive degradation of the corneal tissue mediated by Pseudomonas protease activities, including both Pseudomonas protease IV (PIV) and the P. aeruginosa small protease (PASP). The virulence role of PIV was determined by the reduced virulence of a PIV-deficient mutant relative to its parent strain and the mutant after genetic complementation (rescue). Additionally, the non-ocular pathogen Pseudomonas putida acquired corneal virulence when it produced active PIV from a plasmid-borne piv gene. The virulence of PIV is not limited to the mammalian cornea, as evidenced by its destruction of respiratory surfactant proteins and the cytokine interleukin-22 (IL-22), the key inducer of anti-bacterial peptides. Furthermore, PIV contributes to the P. aeruginosa infection of both insects and plants. A possible limitation of PIV is its inefficient digestion of collagens; however, PASP, in addition to cleaving multiple soluble proteins, is able to efficiently cleave collagens. A PASP-deficient mutant lacks the corneal virulence of its parent or rescue strain evidencing its contribution to corneal damage, especially epithelial erosion. Pseudomonas-secreted proteases contribute importantly to infections of the cornea, mammalian lung, insects, and plants.

Enhancement of laccase activity by pre-incubation with organic solvents

Laccases that are tolerant to organic solvents are powerful bio-catalysts with broad applications in biotechnology. Most of these uses must be accomplished at high concentration of organic solvents, during which proteins undergo unfolding, thereby losing enzyme activity. Here we show that organic-solvent pre-incubation provides effective and reversible 1.5- to 4.0-fold enhancement of enzyme activity of fungal laccases. Several organic solvents, including acetone, methanol, ethanol, DMSO, and DMF had an enhancement effect among all laccases studied. The enhancement was not substrate-specific and could be observed by using both phenolic and non-phenolic substrates. Laccase preincubated with organic solvents was sensitive to high temperature but remained stable at 25 °C, for an advantage for long-term storage. The acetone-pre-incubated 3-D structure of DLac, a high-efficiency fungal laccase, was determined and confirmed that the DLac protein structure remains intact and stable at a high concentration of organic solvent. Moreover, the turnover rates of fungal laccases were improved after organic-solvent pre-incubation, with DLac showing the highest enhancement among the fungal laccases examined. Our investigation sheds light on improving fungal laccase usage under extreme conditions and extends opportunities for bioremediation, decolorization, and organic synthesis.

Purification and biochemical characterization of a novel thermostable protease from the oyster mushroom Pleurotus sajor-caju strain CTM10057 with industrial interest

BACKGROUND

Proteases are hydrolytic enzymes that catalyze peptide linkage cleavage reactions at the level of proteins and peptides with different degrees of specificity. This group draws the attention of industry. More than one protease in three is a serine protease. Classically, they are active at neutral to alkaline pH. The serine proteases are researched for industrial uses, especially detergents. They are the most commercially available enzyme group in the world market. Overall, fungi produced extracellular proteases, easily separated from mycelium by filtration.

RESULTS

A new basidiomycete fungus CTM10057, a hyperproducer of a novel protease (10,500 U/mL), was identified as Pleurotus sajor-caju (oyster mushroom). The enzyme, called SPPS, was purified to homogeneity by heat-treatment (80 °C for 20 min) followed by ammonium sulfate precipitation (35-55%)-dialysis, then UNO Q-6 FPLC ion-exchange chromatography and finally HPLC-ZORBAX PSM 300 HPSEC gel filtration chromatography, and submitted to biochemical characterization assays. The molecular mass was estimated to be 65 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), Native-PAGE, casein-zymography, and size exclusion by HPLC. A high homology with mushroom proteases was displayed by the first 26 amino-acid residues of the NH2-terminal aminoacid sequence. Phenylmethanesulfonyl fluoride (PMSF) and diiodopropyl fluorophosphates (DFP) strongly inhibit SPPS, revealing that it is a member of the serine-proteases family. The pH and temperature optima were 9.5 and 70 °C, respectively. Interestingly, SPPS possesses the most elevated hydrolysis level and catalytic efficiency in comparison with SPTC, Flavourzyme® 500 L, and Thermolysin type X proteases. More remarkably, a high tolerance towards organic solvent tolerance was exhibited by SPPS, together with considerable detergent stability compared to the commercial proteases Thermolysin type X and Flavourzyme® 500 L, respectively.

CONCLUSIONS

This proves the excellent proprieties characterizing SPPS, making it a potential candidate for industrial applications especially detergent formulations.

Improve Salinivibrio zinc-metalloprotease function in less polar organic solvents by increasing surface hydrophobicity

Organic solvents tend to strip water from protein and thereby disrupt non-covalent forces and decrease enzyme activity and stability. In the present study, we have replaced the surface charge residues in Salinivibrio zinc-metalloprotease (SVP) with hydrophobic ones (E12V, D22I, D24A and D310I) in order to study the effects of surface hydrophobicity with hydrophobic strength of organic solvents. Compared to SVP, D24A exhibited an increase in k_cat and catalytic efficiency and a reduction in thermal inactivation rate in aqueous solvent. Structural studies indicated that the replacement of surface charge residues with hydrophobic residues would not induce conformational changes. C₅₀ value (the value of solvent concentration where 50% of enzyme activity remains), k_i (irreversible thermoinactivation rate), and kinetic parameters of E12V, D22I, and D24A were higher in isopropanol and n-propanol. D24A is found to be the most efficient mutant for its remarkable decrease in k_i value in the presence of isopropanol and n-propanol and a reduction in k_i value in the presence of dimethylformamide (DMF) and methanol. C₅₀ value in this variant was increased about 1.2% in DMF, 2% in methanol and isopropanol and 2.5% in n-propanol. Results revealed that, there was a correlation between surface hydrophobicity of SVP and hydrophobic strength of organic solvents.

Bioconversion of shrimp waste Penaeus merguiensis using lactic acid fermentation: An alternative procedure for chemical extraction of chitin and chitosan

Chitin extraction from shrimp wastes by biological treatment, using the Pseudomonas aeruginosa was a positive and simple method. In order to look for the optimal conditions, the wastes were incubated at 30°C and 100rpm in different glucose (0%, 10%, 15% and 20%) and inoculation (10%, 15% and 20%) concentrations for 4 and 6days. At the end of fermentation, Protease activity was investigated at different temperatures and temperature 50°C was considered as the optimum. The results obtained also showed a direct relationship between the concentration of different parameters and deproteinization and demineralization rates, so that the optimal conditions were 20% glucose, 20% inoculation and 6days fermentation. These conditions led to 82% demineralization, 92% deproteinization and chitin yield of 47%. Then, chitin was converted to chitosan using microwave, autoclave and traditional methods. The highest yield (87%) was obtained with autoclave method. At the end, the chitin and chitosan were characterized by elemental analysis and FTIR.

Purification and characterization of a thermo- and organic solvent-tolerant alkaline protease from Bacillus sp. JER02

Bacillus sp. JER02 is a bacterial strain that can be grown in a medium containing organic solvents and produce a protease enzyme. JER02 protease was purified with a yield of 31.9% of total protein and 328.83-fold purification. Km and Vmax of this protease were established as 0.826 µM and 7.18 µmol/min, respectively. JER02 protease stability was stimulated about 80% by cyclohexane. It exhibited optimum temperature activity at 70°C. Furthermore, this enzyme was active in a wide range of pH (4-12) and showed maximum activity at pH 9.0. The nonionic detergents Tween-20 and Triton X-100 improved the protease activity by 30 and 20%, respectively. In addition, this enzyme was shown to be very stable in the presence of strong anionic surfactants and oxidizing agents, since it retained 77%, 93%, and 98% of its initial activity, after 1 hr of incubation at room temperature with sodium dodecyl sulfate (SDS), sodium perborate (1%, v/v) and H2O2 (1%, v/v), respectively. Overall, the unique properties of the Bacillus sp. JER02 protease suggested that this thermo- and detergent-stable, solvent-tolerant protease has great potential for industrial applications.

Modification of recombinant elastase expressed in Pichia pastoris by introduction of N-glycosylation sites

A novel N-glycosylation site was introduced into recombinant elastase (rPAE) at N36, N67, or N264 through the site-directed mutagenesis of I38T, A69T, or N266T, respectively. The A69T mutation completely inhibited the expression of rPAE. As expected, the I38T and N266T mutant proteins exhibited higher degrees of N-glycosylation compared with the wild type rPAE. The I38T mutant was more efficient in the hydrolysis of casein in aqueous medium and exhibited higher specific activity and k(cat) values and a lower K(m) value. In contrast, the N266T mutant and the wild type displayed similar values. Importantly, the I38T mutant achieved in higher rates and yields of peptide synthesis in 50% (v/v) dimethylsulfoxide, whereas the N266T mutant was similar to the wild type rPAE. Furthermore, the maximum yield of Z-Ala-Phe-NH2 synthesis catalyzed by the I38T mutant protein (87%) was higher than those achieved by the wild type (78%) and N266T mutant (78%) proteins. Neither the I38T nor the N266T mutation exerted significant effects on the rPAE solvent stability. In aqueous medium, the I38T mutation decreased the rPAE thermostability, and the N266T mutation slightly improved that. In conclusion, the I38T mutation improved the potential of rPAE in industrial applications.

Characterization of solvent stable extracellular protease from Bacillus koreensis (BK-P21A)

A total of 18 protease producing bacterial strains were isolated from detergent effluent in South Korea using skim milk agar medium. A strain (BK-P21A) was selected and identified as Bacillus koreensis based on morphological, biochemical and molecular characterizations (16S rRNA gene sequence analysis). Optimized culture conditions for the production of protease were pH 8.5, 30 °C, sucrose (2%) and yeast extract (0.2%) during 36 h of incubation. Furthermore, the protease was partially purified by ammonium sulphate precipitation (80%) and again by Superdex 200 10/300 GL and Superdex 75 10/300 GL column chromatography, which resulted in 5.0 fold purification and a yield of 23%. The molecular mass of the protease was estimated to be 48 kDa by SDS-PAGE. The purified enzyme was further characterized and found to be most active at pH 9.0 and 60 °C. The activity of the purified protease was enhanced by CaCl₂ and CoCl₂, but inhibited by PMSF, which indicated it was a serine type protease. Moreover, the protease was moderately stable in surfactants and 81% stable in H₂O₂. Finally, the enzyme was more active and stable (94-126.5%) in various hydrophilic organic solvents. Considering the stability of protease towards the alkaline pH, high temperature and organic solvents (50%), the enzyme from B. koreensis can be used as an alternative biocatalyst for several industrial applications mainly for peptide synthesis in nonaqueous solvents.

Downstream processing, characterization, and structure-function relationship of solvent-, detergent-, psychro-, thermo-, alkalistable metalloprotease from metal-, solvent-tolerant psychrotrophic Pseudomonas putida SKG-1 isolate

The purification and characterization of psychro-thermoalkalistable protease from psychrotrophic Pseudomonas putida isolate is being reported for the first time. A ~53 kDa protease was purified 21.4-folds with 57.2% recovery by ultrafiltration and hydrophobic interaction chromatography. Kinetic analyses revealed the K(m) and V(max) to be 1.169 mg mL(-1) and 0.833 mg mL(-1) min(-1) , respectively. The k(cat) value of 3.05 × 10(2) s(-1) indicated high affinity and catalytic efficiency toward casein. The protease was most active at pH 9.5 and 40°C, with 100% stability in pH and temperature range of 6.0-11.0 and 10-40°C, respectively. Presence of Zn(2+) increased the thermostability of protease (at 70°C) by 433%. Ethylene diamine tetra acetic acid (EDTA) and 1,10-phenanthroline were inhibitory, whereas phenyl methyl sulfonyl fluoride (PMSF), p-chloro mercuric benzoate (PCMB), and β-mercaptoethanol were ineffective, revealing the enzyme to be a metalloprotease. Zinc, calcium, iron, nickel, and copper at 1 mM increased the enzyme activity (102-134%). Complete reversion of enzyme inhibition (caused by Ethylene diamine tetra acetic acid [EDTA]) by Zn(2+) affirmed this enzyme as zinc-dependent metalloprotease. At 0.1% concentration, Triton X-100 and Tween 80 slightly increased, while SDS and H(2) O(2) reduced the protease activity. In the presence of 0.1% commercial detergents, the enzyme was fairly stable (54-81%). In the presence of organic solvent, the protease was remarkably stable exhibiting 72-191% activities. In contrast, savinase exhibited good stability in the presence of hydrophilic solvents, while chymotrypsin showed elevated activities with benzene, toluene, and xylene only. Circular dichroism analysis revealed the protease as a β-rich protein, having large fraction (∼40%) of β-sheets. Presence of different environmental conditions altered the β-content, which accordingly affected the protease activity.

A mutant leucine aminopeptidase from Streptomyces cinnamoneus with enhanced L-aspartyl L-amino acid methyl ester synthetic activity

L-aspartyl L-amino acid methyl ester was synthesized using a mutant of a thermostable leucine aminopeptidase from Streptomyces cinnamoneus, D198 K SSAP, obtained in previously. A peptide of high-intensity sweetener, L-aspartyl-L-phenylalanine methyl ester, was selected as a model for demonstrating the synthesis of L-aspartyl L-amino acid methyl ester. The hydrolytic activities of D198 K SSAP toward L-aspartyl-L-phenylalanine and its methyl ester were, respectively, 74-fold and fourfold higher than those of wild type. Similarly, the initial rate of the enzyme for L-aspartyl-L-phenylalanine methyl ester synthesis was over fivefold higher than that of wild-type SSAP in 90% methanol (v/v) in a one-pot reaction. Furthermore, other L-aspartyl L-amino acid methyl esters were synthesized efficiently using D198 K SSAP. Results show that the substitution of Asp198 of SSAP with Lys is effective for synthesizing L-aspartyl L-amino acid methyl ester.

Analyzing the molecular basis of enzyme stability in ethanol/water mixtures using molecular dynamics simulations

One of the drawbacks of nonaqueous enzymology is the fact that enzymes tend to be less stable in organic solvents than in water. There are, however, some enzymes that display very high stabilities in nonaqueous media. In order to take full advantage of the use of nonaqueous solvents in enzyme catalysis, it is essential to elucidate the molecular basis of enzyme stability in these media. Toward this end, we performed μs-long molecular dynamics simulations using two homologous proteases, pseudolysin, and thermolysin, which are known to have considerably different stabilities in solutions containing ethanol. The analysis of the simulations indicates that pseudolysin is more stable than thermolysin in ethanol/water mixtures and that the disulfide bridge between C30 and C58 is important for the stability of the former enzyme, which is consistent with previous experimental observations. Our results indicate that thermolysin has a higher tendency to interact with ethanol molecules (especially through van der Waals contacts) than pseudolysin, which can lead to the disruption of intraprotein hydrophobic interactions and ultimately result in protein unfolding. In the absence of the C30-C58 disulfide bridge, pseudolysin undergoes larger conformational changes, becoming more open and more permeable to ethanol molecules which accumulate in its interior and form hydrophobic interactions with the enzyme, destroying its structure. Our observations are not only in good agreement with several previous experimental findings on the stability of the enzymes studied in ethanol/water mixtures but also give an insight on the molecular determinants of this stability. Our findings may, therefore, be useful in the rational development of enzymes with increased stability in these media.

Role of α-helical structure in organic solvent-activated homodimer of elastase strain K

Recombinant elastase strain K overexpressed from E. coli KRX/pCon2(3) was purified to homogeneity by a combination of hydrophobic interaction chromatography and ion exchange chromatography, with a final yield of 48% and a 25-fold increase in specific activity. The purified protein had exhibited a first ever reported homodimer size of 65 kDa by SDS-PAGE and MALDI-TOF, a size which is totally distinct from that of typically reported 33 kDa monomer from P. aeruginosa. The organic solvent stability experiment had demonstrated a stability pattern which completely opposed the rules laid out in previous reports in which activity stability and enhancement were observed in hydrophilic organic solvents such as DMSO, methanol, ethanol and 1-propanol. The high stability and enhancement of the enzyme in hydrophilic solvents were explained from the view of alteration in secondary structures. Elastinolytic activation and stability were observed in 25 and 50% of methanol, respectively, despite slight reduction in α-helical structure caused upon the addition of the solvent. Further characterization experiments had postulated great stability and enhancement of elastase strain K in broad range of temperatures, pHs, metal ions, surfactants, denaturing agents and substrate specificity, indicating its potential application in detergent formulation.

A novel nonionic surfactant- and solvent-stable alkaline serine protease from Serratia sp. SYBC H with duckweed as nitrogen source: production, purification, characteristics and application

A novel nonionic surfactant- and hydrophilic solvent-stable alkaline serine protease was purified from the culture supernatant of Serratia sp. SYBC H with duckweed as nitrogen source. The molecular mass of the purified protease is about 59 kDa as assayed via SDS-PAGE. The protease is highly active over the pH range between 5.0 and 11.0, with the maximum activity at pH 8.0. It is also fairly active over the temperature range between 30 and 80°C, with the maximum activity at 40°C. The protease activity was substantially stimulated by Mn(2+) and Na(+) (5 mM), up to 837.9 and 134.5% at 40°C, respectively. In addition, Mn(2+) enhanced the thermostability of the protease significantly at 60°C. Over 90% of its initial activity remained even after incubating for 60 min at 40°C in 50% (v/v) hydrophilic organic solvents such as DMF, DMSO, acetone and MeOH. The protease retained 81.7, 83.6 and 76.2% of its initial activity in the presence of nonionic surfactants 20% (v/v) Tween 80, 25% (v/v) glycerol and Triton X-100, respectively. The protease is strongly inhibited by PMSF, suggesting that it is a serine protease. Washing experiments revealed that the protease has an excellent ability to remove blood stains.

Purification of Protease from Pseudomonas thermaerum GW1 Isolated from Poultry Waste Site

An extracellular protease was purified from Pseudomonas thermaerum GW1 a new strain identified by morphological, biochemical and 16S rDNA sequencing. It was isolated from soil of Poultry waste site at Ghazipur near Ghaziabad, Delhi. The strain produces extra cellular protease in the culture media that was maintained at 37°C, 140 rpm. The media was harvested for protease after 48 hrs of incubation at 37°C in basal media supplemented with 1% casein. We report 6.08 fold purification of enzyme following ammonium sulphate precipitation and DEAE-cellulose chromatography. The molecular weight of the enzyme was estimated to be approximately 43,000 daltons as shown by casein zymography studies. The optimum pH for the proteolytic activity was pH 8.0 and enzyme remained stable between pH 5 -11 at 60°C. Interestingly Mn²⁺ (5mM) activated enzyme activity by 5 fold, while Cu²⁺, Mg²⁺and Ca²⁺ moderately activated enzyme activity, where as Zn²⁺, Fe²⁺ and Hg²⁺ inhibited enzyme activity. The protease produced was stable in presence of 50 % (v/v) ethylacetate and acetone. Isopropanol, methanol and benzene increased protease activity by 2.7, 1.3 and 1.1 fold respectively but was inhibited in presence of glycerol and DMSO. This organic solvent-stable protease could be used as a biocatalyst for enzymatic peptide synthesis

An oxidant- and organic solvent-resistant alkaline metalloprotease from Streptomyces olivochromogenes

Organic solvent- and detergent-resistant proteases are important from an industrial viewpoint. However, they have been less frequently reported and only few of them are from actinomycetes. A metalloprotease from Streptomyces olivochromogenes (SOMP) was purified by ion exchange with Poros HQ and gel filtration with Sepharose CL-6B. Apparent molecular mass of the enzyme was estimated to be 51 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gelatin zymography. The activity was optimum at pH 7.5 and 50 degrees C and stable between pH 7.0 and 10.0. SOMP was stable below 45 degrees C and Ca(2+) increased its thermostability. Ca(2+) enhanced while Co(2+), Cu(2+), Zn(2+), Mn(2+), and Fe(2+) inhibited the activity. Ethylenediaminetetraacetic acid and ethylene glycol-bis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, but not phenylmethylsulfonyl fluoride, aprotinin, and pefabloc SC, significantly suppressed the activity, suggesting that it might be a metalloprotease. Importantly, it is highly resistant against various detergents, organic solvents, and oxidizing agents, and the activity is enhanced by H(2)O(2). The enzyme could be a novel protease based on its origin and peculiar biochemical properties. It may be useful in biotechnological applications especially for organic solvent-based enzymatic synthesis.

Enhancement of the aspartame precursor synthetic activity of an organic solvent-stable protease

The PST-01 protease is highly stable and catalyzes the synthesis of the aspartame precursor with high reaction yields in the presence of organic solvents. However, the synthesis rate using the PST-01 protease was slower than that observed when thermolysin was used. Structural comparison of both enzymes showed particular amino acid differences near the active center. These few residue differences in the PST-01 protease were mutated to match those amino acid types found in thermolysin. The mutated PST-01 proteases at the 114th residue from tyrosine to phenylalanine showed enhancement of synthetic activity. This activity was found to be similar to thermolysin. In addition, mutating the residue in the PST-01 protease with arginine and serine showed more improvement of the activity. The mutant PST-01 protease should be more useful than thermolysin for the synthesis of the aspartame precursor, because this enzyme has higher stability and activity in the presence of organic solvents. The results show the potential of organic solvent-stable enzymes as industrial catalysts.

Purification and characterization of a salt-activated and organic solvent-stable heterotrimer proteinase from Virgibacillus sp. SK33 isolated from Thai fish sauce

A NaCl-activated proteinase produced by Virgibacillus sp. SK33 was purified to homogeneity using phenyl-Sepharose and Sephadex G-75 with a yield of 12% and purification of 2.6-fold. A single protein was detected at approximately 32 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. However, three subunits with molecular weights of 27,858, 33,918, and 35,368 Da were obtained from MALDI-TOF mass spectra, implying that the enzyme was a heterotrimer. The isoelectric point of the proteinase was 5.4. Optimum catalytic activity was at 55 degrees C and pH 7.5. The enzyme showed serine characteristics as it was completely inhibited by phenylmethanesulfonyl fluoride. The purified proteinase showed broad specificity toward oxidized insulin B including Gln4, Cys7, Glu13, Ala14, Leu15,17, Tyr16,26, Arg22, Phe24,25, and Lys29. Dominant cleavage sites of the enzyme were Tyr16-Leu17 and Phe25-Tyr26, indicating that it preferably hydrolyzed aromatic amino acids located on the P1 site. Among various substrates studied, the enzyme hydrolyzed anchovy protein to the greatest extent at 4 M NaCl. Activity increased with either CaCl2 or NaCl concentration with the maximum 2-fold increase at either 50 mM CaCl2 or 4 M NaCl. The enzyme was also highly stable up to 500 mM CaCl2 or 4 M NaCl. The proteinase showed high stability in various organic solvents (25%, v/v) including dimethylsulfoxide, methanol, acetonitrile, and ethanol. Results of peptide mass fingerprint and de novo peptide sequencing showed that the purified proteinase is a novel proteinase. The proteinase from Virgibacillus sp. SK33 could have a potential application in high ionic strength environments and aqueous-organic solvent systems.

Enzymes from solvent-tolerant microbes: useful biocatalysts for non-aqueous enzymology

Solvent-tolerant microbes are a newly emerging class that possesses the unique ability to thrive in the presence of organic solvents. Their enzymes adapted to mediate cellular and metabolic processes in a solvent-rich environment and are logically stable in the presence of organic solvents. Enzyme catalysis in non-aqueous/low-water media is finding increasing applications for the synthesis of industrially important products, namely peptides, esters, and other trans-esterification products. Solvent stability, however, remains a prerequisite for employing enzymes in non-aqueous systems. Enzymes, in general, get inactivated or give very low rates of reaction in non-aqueous media. Thus, early efforts, and even some recent ones, have aimed at stabilization of enzymes in organic media by immobilization, surface modifications, mutagenesis, and protein engineering. Enzymes from solvent-tolerant microbes appear to be the choicest source for studying solvent-stable enzymes because of their unique ability to survive in the presence of a range of organic solvents. These bacteria circumvent the solvent's toxic effects by virtue of various adaptations, e.g. at the level of the cytoplasmic membrane, by degradation and transformation of solvents, and by active excretion of solvents. The recent screening of these exotic microbes has generated some naturally solvent-stable proteases, lipases, cholesterol oxidase, cholesterol esterase, cyclodextrin glucanotransferase, and other important enzymes. The unique properties of these novel biocatalysts have great potential for applications in non-aqueous enzymology for a range of industrial processes.