Fungal Proteolytic Enzymes

Two kinds of proteolytic enzyme, tentatively named acid protease A and B which showed a single peak on electrophoresis individually, were isolated from the crude enzyme powder obtained from the broth filtrate cultured with Asper gillus niger var. macrosporus. Acid protease B is similar too the fungal acid protease previously reported, bccause the enzyme exhibits optimum activity on milk casein at about pH 2.6 and 55°C when the incubation was done at pH 2.6. Acid protease A is a new proteolytic enzyme, because the enzyme exhibits optimum activity on milk casein at about 2.0 and 70°C or 60°C when the incubation was done at pH 2.6 or 1.5 respectively.     

Cloning,expression, and characterization of serine protease from thermophilic fungus <Emphasis Type="Italic">Thermoascus aurantiacus</Emphasis> var. <Emphasis Type="Italic">levisporus</Emphasis>

The serine protease gene from a thermophilic fungus Thermoascus aurantiacus var. levisporus, was cloned, sequenced, and expressed in Pichia pastoris and the recombinant protein was characterized. The full-length cDNA of 2,592 bp contains an ORF of 1,482 bp encoding 494 amino acids. Sequence analysis of the deduced amino acid sequence revealed high homology with subtilisin serine proteases. The putative enzyme contained catalytic domain with active sites formed by three residues of Aspl83, His215, and Ser384. The molecular mass of the recombinant enzyme was estimated to be 59.1 kDa after overexpression in P. pastoris. The activity of recombinant protein was 115.58 U/mg. The protease exhibited its maximal activity at 50°C and pH 8.0 and kept thermostable at 60°C, and retained 60% activity after 60 min at 70° C. The protease activity was found to be inhibited by PMSF, but not by DTT or EDTA. The enzyme has broad substrate specificity such as gelatin, casein and pure milk, and exhibiting highest activity towards casein.     

Studies on Lotus Seed Protease

A protease from the lotus seed (Nelumbo nucifera Gaertn) was purified by acid-treatment, ammonium sulfate-fractionation, ethylalcohol-fractionation, TEAE-cellulose-treatment and Sephadex G-100 gel-filtration.

The enzyme was purified about 870-fold and was homogeneous in electrophoretic and ultracentrifugal analyses.

Purified lotus seed protease is an acid protease with a pH optimum at 3.8 toward urea-denatured casein. It is active for casein and hemoglobin. But other proteins such as edestin, zein, lotus seed globulin and soybean casein are slightly hydrolyzed and egg albumin is hardly hydrolyzed. This enzyme is most stable at pH 4.0 below 40°C. The enzyme is not a thiol protease, and its activity was completely inhibited by potassium permanganate, remarkably inhibited by sodium dodecylsulfate and accelerated by hydrogen peroxide.     

Crystallization and Some Properties of Alkaline Proteinase from Aspergillus sulphureus

An alkaline proteinase of Aspergillus sulphureus (Fresenius) Thorn et Church has been purified in good yields from wheat bran culture by fractionation with ammonium sulfate, treatment with acrynol, and DEAE-Sephadex A-50 column chromatography. The crystalline preparation was homogeneous on sedimentation analysis and polyacrylamide gel zone electrophoresis. The molecular weight was calculated to be 23,000 by gel filtration. The amino acid composition of the enzyme was determined. The enzyme did not precipitate with acrynol. Optimum pH for the hydrolysis of casein was 7 to 10 at 35°G for 15 min. Optimum temperature was 50°C at pH 7 for 10 min. The enzyme was highly stable at the range of pH 6 to 11 at 5°C, whereas relatively stable at pH 6 to 7 at 35°C. Metalic salts tested did not affect activity. Chelating agents, sulfhydryl reagents, TPCK, and oxidizing or reducing reagents tested, except iodine, had no effect on the activity. Diisopro-pylfluorophosphate and N-bromosuccinimide almost completely inactivated the proteinase.     

Milk Clotting Enzyme from Microorganisms

Out of some 800 strains of microorganisms, a potent fungus for milk clotting enzyme was isolated from soil during the course of screening tests and was identified as one of strains of Mucor pusillus Lindt. Satisfactory results were obtained in cheese making experiments with this enzyme which could be produced effectively by solid culture on wheat bran at 30°C for about 70 hrs.

The balance between milk clotting activity and proteolytic activity of this enzyme resembled very much to that of rennet.

Microbial rennet from Mucor pusillus F-27 was obtained with high productivity by solid culture followed by water extraction. The enzyme could be precipitated by salting out with ammonium sulfate and also by mixing with various water-miscible organic solvents such as ethanol, methanol or acetone.

This enzyme is one of acid proteases having its optimal pH for milk casein digestion around 3.5. The ratio of milk clotting activity to proteolytic activity of this enzyme resembled that of calf rennet than those of other proteases of fungal origin. This was more heat stable and more resistant against pH changes than animal rennet. Apparent activity of milk clotting was more affected by Ca ion concentration in milk than that of calf rennet.

The liberation of 12% TCA soluble nitrogen from casein fraction was a little less specific than that of calf rennet. The optimal temperature for milk clotting lay around 56°C.

Electrophoretic patterns of α-peak of casein treated with this enzyme showed the weak proteolysis which resembled that with rennet.     

Degradation of staphylococcal enterotoxin A by a Pseudomonas aeruginosa isolate from raw milk

Recently, we found that staphylococcal enterotoxin A (SEA)-producing Staphylococcus aureus strains produced SEA in raw milk with microbial contaminants at high temperatures like 40 °C only. Moreover, the concentration of SEA produced in raw milk gradually decreased after the peak. The reason(s) for SEA degradation in raw milk was studied in this study. Degradation of SEA spiked in raw milk was observed at 40 °C, but not at 25 °C. A Pseudomonas aeruginosa isolate from raw milk degraded SEA spiked in broth at 40 °C. A sample partially purified with a chromatographic method from culture supernatant of the isolate degraded SEA. Two main proteolytic bands were observed in the sample by zymographic analysis with casein. These results suggested that the SEA in raw milk might be degraded by a protease(s) produced by the P. aeruginosa isolate. This finding might be the first report on SEA degradation by a proteolytic enzyme(s) derived from Pseudomonas bacteria to our knowledge.     

Studies on Protein Metabolism in Higher Plants

A leaf protease of tobacco whose activity was enhanced during curing was purified about 60 times with ammonium sulfate fractionation, ethanol precipitation, calcium phosphate gel treatment and Sephadex G-200 column chromatography, and some properties of the protease were examined. The purified enzyme showed the optimum pH at 5.5 and the optimum temperature at 60°C. The protease activity was stable between pH 4.5 and 5.5 at 50°G or at pH 5.5 below 40°C for 1 hr, but completely destroyed at 70°C during 1 hr. The protease activity was greatly activated by reducing agents such as cysteine, glutathione or mercaptoethanol and inhibited by p-chloromercuribenzoate, phenyl- mercuric acetate or silver ions. Metal ions except for silver ion and ethylenediamine tetraacetic acid did not affect the protease activity so far examined.     

Enzymatic Properties of Alkaline Proteinase from Aspergillus candidus

Some enzymatic properties were examined with the purified alkaline proteinase from Aspergillus candidus. The isoelectric point was determined to be 4.9 by polyacrylamide gel disc electrofocusing. The optimum pH for milk casein was around 11.0 to 11.5 at 30°C. The maximum activity was found at 47°C at pH 7.0 for 10 min. The enzyme was stable between pH 5.0 and 9.0 at 30°C and most stable at pH 6.0 at 50°C. The enzyme activity over 95% remained at 40°C, but was almost completely lost at 60°C for 10 min. Calcium ions protected the enzyme from heat denaturation to some extent. No metal ions examined showed stimulatory effect and Hg²⁺ ions inhibited the enzyme. The enzyme was also inhibited by potato inhibitor and diisopropylphosphorofluoridate, but not by metal chelating agent or sulfhydryl reagents. A. candidus alkaline proteinase exhibited immunological cross-reacting properties similar to those of alkaline proteinases of A. sojae and A. oryzae.     

Chemical Modification of Neutral Protease from Bacillus subtilis var. amylosacchariticus: Assignment of Tyrosyl Residues Iodinated

The neutral protease of Bacillus subtilis var. amylosacchariticus (B. amylosacchariticus) was iodinated with a 25-fold molar excess of iodine at pH 9.4 for 3 min at 0°C, by which treatment the proteolytic activity toward casein was markedly reduced, while the hydrolytic activity toward an N-blocked peptide substrate was rather increased. The modified enzyme was digested with Staphylococcus aureus V8 protease at pH 8.0 and the amino acid sequences of resultant peptides were compared with those obtained from the native enzyme. One of the peptides was found to have an amino acid sequence of Thr-Ala-Asn-Leu-Ile-Tyr-Glu, which corresponds to residue Nos. 153—159 of the enzyme, where Tyr-158 was identified to be mono-iodotyrosine. The other two peptides were those containing Tyr-21 which was mono- and di-iodinated, respectively. Referring to nitration experiments on the neutral protease and the active site structure of thermolysin, it was concluded that the iodination of Tyr-158 is mainly responsible for the activity changes of B. amylosacchariticus neutral protease.     

Surface display of acid protease on the cells of Yarrowia lipolytica for milk clotting

The acid protease structural gene was amplified from the genomic DNA of Saccharomycopsis fibuligera A11. When the gene was cloned into the multiple cloning site of the surface display vector pINA1317-YlCWP110 and expressed in the cells of Yarrowia lipolytica, the cells displaying the acid protease could form clear zone on the plate-containing milk indicating that they had extracellular acid protease activity. The cells displaying the acid protease can be used to effectively clot skimmed milk. The highest clotting milk activity (1,142.9 U/ml) was observed under the conditions of pH 3.0, 40 °C, 20 mM of CaCl₂, and 10% skimmed milk powder. We found that the acid protease displayed on the cells of Y. lipolytica which has generally regarded as safe status could be easily isolated and concentrated compared to the free acid protease. Therefore, the displayed acid protease may have many potential applications in food and cheese industries. This is the first report that the yeast cells displaying the acid protease were used to clot milk.     

Acid Protease of Bovine Milk

Occurrence of milk acid protease in bovine casein in addition to alkaline protease was found and purification of this enzyme was achieved. The enzyme had a pH optimum at 4.0 and was most stable at pH 3.5. The molecular weight of the enzyme was 36,000 and no inhibition was observed by diisopropyl-fluorophosphate, EDTA etc. This enzyme is considered to be similar to cathepsin D.

Milk acid protease mainly hydrolyzed α_s-casein and similar change was observed in autolysis of casein at pH 5.5. It is suggested that milk acid protease may have some significance in cheese ripening.     

Properties of Extracellular Enzymes from Aphanomyces astaci and Their Relevance in the Penetration Process of Crayfish Cuticle

In culture filtrates from the crayfish plague parasite, Aphanomyces astaci, protease and a low level of hyaluronidase activity were found. The hyaluronidase activity was highest at pH 6.5 or above and at about 23°C. The protease activity had a broad pH-optimum, between pH 7 and at least pH 10, and was partially denatured at 30°C. However, when incubated for 30 min with the substrate, casein, the activity increased logarithmically up to about 35–40°C and had an apparent optimum at 45–50°C. The proteases from the parasitic as well as from two less proteolytic, saprophytic Aphanomyces species were predominantly constitutive and were excreted mainly by the older mycelia. Proteases from the parasite and a saprophyte did not reach full activity until 10–30 min after substrate addition. No lipase activity was found in the case of the mycelium of the parasitic species. However, esterase was apparently present inside germinating zoospores. The native enzymes of A. astaci could degrade freeze-dried soft cuticle from crayfish. The relevance of the different enzymes of A. astaci for the penetration process within the cuticle of crayfish is discussed.     

Purification of alkaline proteases from a Bacillus strain and their possible interrelationship

 Alkalophilic Bacillus sp. KSM-K16 produced three alkaline proteases, as detected by polyacrylamide gel electrophoresis (PAGE). The major protease, designated M protease, was recently purified to homogeneity and its properties were characterized. In the present study, two minor proteases, designated H protease and N protease, were purified to homogeneity from cultures of this organism. H protease had a molecular mass of 28 kDa, as estimated by sodium dodecyl sulfate/PAGE (SDS-PAGE) and its maximum activity against casein was observed at pH 11.0 and at 55^°C. N protease consisted of two polypeptide chains with molecular masses of 12.5 kDa and 14.5 kDa, as estimated by SDS-PAGE, although it migrated as a single protein band during non-denaturing PAGE. Its maximum activity was observed at pH 11.0 and at 60^°C. The amino-terminal sequences of H protease and of the 14.5-kDa polypeptide of N protease were identical to that of M protease. The electrophoretic relationship between the three enzymes was examined after they had been stored at different pH values and at 5^°C. M protease was converted to H protease more rapidly at pH 11 than at pH 8 or below, and H protease was converted to M protease at pH 8 or below but not at pH 11. N protease appeared to be the autolytic product of the M and H proteases. Received: 12 December 1994/Received last revision: 9 June 1995/Accepted: 31 July 1995     

Application of protease from Nocardiopsis sp. as a laundry detergent additive

The application of protease as a laundry detergent additive from a newly isolated Nocardiopsis sp., isolated from a soil sample collected in Northeast Brazil is reported. The optimal pH and temperature for protease activity were pH 10.5 and 50 °C, respectively. The enzyme was stable in a long-term incubation, showed 73.5% of initial activity at pH 10.5 and 61.7% at pH 12.0 for 120 min. Approximately 60% of initial activity remained after 120 min at 50 °C or after 30 min at 80 °C. Almost 87% of enzyme activity was retained in the presence of 10% (v/v) of peroxide at 40 °C, after 1 h. The protease also was stable in the presence of oxidants and surfactants such as SDS, saponin, Tween 20 and Tween 80 after 30 min. In the presence of Omo^®, the enzyme retained 64% of its activity at 40 °C for 1 h. An increase in the proteolytic activity (6–17%) was observed with K⁺, Na⁺, and Mg⁺⁺ ions. At pH 8.0, the protease hydrolysed casein maximally (50 U/mg).     

A new kumamolisin-like protease from Alicyclobacillus acidocaldarius: an enzyme active under extreme acidic conditions

A new serine-carboxyl proteinase, called kumamolisin-ac, was purified from the thermoacidophilic bacterium Alicyclobacillus acidocaldarius. The enzyme is a monomeric protein of 45?kDa, active over a wide temperature range (5.0–70°C) and extremely acidic pHs (1.0–4.0), showing maximal proteolytic activity at pH?2.0 and 60°C. Interestingly, kumamolisin-ac displayed a significant proteolytic activity even at 5°C, thus suggesting a sort of cold-adaptation for this enzyme. The protease was remarkably stable at high temperatures (t_1/2 at 80°C, 10?h, pH?2.0) and over a broad range of pH (2.0–7.0). Substrate analysis indicated that kumamolisin-ac was active on a variety of macromolecular substrates, such as haemoglobin, hide powder azure, and azocoll. In particular, a high specific activity was detected towards collagen. The corresponding gene was cloned, expressed and the recombinant protease, was found to be homologous to proteases of the ‘S53’ family. From the high identity with kumamolisin and kumamolisin-As, known as collagenolytic proteases, kumamolisin-ac can be considered as the third collagenolytic affiliate within the ‘S53’ family. Cleavage specificity investigation of kumamolisin-ac revealed a unique primary cleavage site in bovine insulin B-chain, whereas a broad specificity was detected using bovine α-globin as substrate. Thus, kumamolisin-ac could represent an attractive candidate for industrial-scale biopeptide production under thermoacidophilic conditions.     

Extraction,purification, and biochemical characterization of serine protease from leaves of Abrus precatorius

A protease from fresh leaves of Abrus precatorius was purified using two classical chromatography techniques: ion-exchange (DEAE-Sepharose) and Gel filtration (Sephadex G-75). The purified protease showed a molecular weight of ～?28?kDa on sodium dodecyl sulfate polyacrylamide gel electrophoresis. The optimum pH and temperature for the purified protease was 8 and 40°C, respectively. The purified protease was stable throughout a wide temperature range from 10 to 80°C and pH from 2 to 12. Protease activity was inhibited in the presence of Co²⁺, Ni²⁺, Hg²⁺, and Zn²⁺ while its activity has increased in the presence of Ca²⁺ and Mg²⁺. The protease was highly specific to casein when compared to its specificity for gelatin, bovine serum albumin, hemoglobin, and defatted flour of Ricinodendron heudelotii. Its V_max and K_m determined using casein as a substrate were 94.34?U/mL and 349.07?µg/mL respectively. Inhibition studies showed that this purified protease was inhibited by both phenylmethane sulfonyl fluoride and aprotinin which are recognized as competitive inhibitors of serine proteases.     

Purification,Crystallization and Some Enzymatic Properties of Acid Protease of Cladosporium sp. No. 45–2

An acid protease of Cladosporium sp. No. 45–2 was purified and crystallized by precipitation with ammonium sulfate, fractional precipitation with acetone, and pH adjustment. About 600 mg of third crystallized preparation was obtained from one liter of culture broth. The purified enzyme was chromatographically homogeneous and confirmed to be monodispersive by physicochemical criteria such as uhracentrifugal and electrophoretical analysis. The enzyme was most active at pH values between 2.5 and 2.7 toward both casein and hemoglobin and was stable at pH values from 2.5 to 7.0 on twenty hour incubation at 30°C.

Millimolar concentration of sodium lauryl sulfate markedly inhibited the enzyme, wheares diisopropyl phosphorofluoridate, sulfhydryl reagents, ethylenediaminetetra acetic acid, and divalent metal ion relatively little affected the activity. The enzyme was most resistant toward S-PI among the acid proteases tested.     

Production of Extracellular Acid Proteases by Aspergillus Clavatus

The production of extracellular acid proteases from Aspergillus clavatus was evaluated in a culture filtrate medium, with different carbon and nitrogen sources. The fungus was cultivated at three different temperatures during 10 days. The proteolytic activity was determined on haemoglobin pH 5.0 at 37 °C. The highest acid proteolytic activity (80 U/ml) was observed in culture medium containing glucose and gelatin at 1%(w/v) at 30 °C at the third day of incubation. Cultures developed in Vogel medium with glucose at 2%(w/v) showed at about 45% of proteolytic activity when compared to the cultures with 1% of the same sugar. The optimum pH of enzymatic activity was 2.0 and the enzyme was stable at pH values ranging from 2.0 to 4.0. The optimum temperature was 40 °C and the half-lives at 40, 45 and 50 °C were 30, 10 and 5 min, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Isolation,identification and some cultural conditionsof a protease-producing thermophilic Streptomyces straingrown on chicken feather as a substrate

Six strains of thermophilic actinomycetes were isolated from soil using an enrichmenttechnique with feathers as the sole carbon and nitrogen source. They showed clear proteolyticactivity on casein agar medium. The most active strain was tentatively identified as Streptomycesthermonitrificans. This isolate was grown in a basal medium with feathers and:or other carbon andnitrogen sources. Supernatant from centrifuged cultures was examined for protease activity andtemperature and pH optima were determined for enzyme activity. Optimum proteolytic activity onbasal liquid medium containing 1% chicken feather pieces was obtained at 50°C, in a mediumadjusted at pH8 and incubated for 72 h at 150 rpm. Proteolytic activity was further increased by1.5% feather pieces and the time required for maximal activity was 96 h. The keratinolytic activityof S. thermonitrificans was examined by incubation with native chicken feather pieces and it wasfound that it is significantly active. The degradation of whole intact feathers by S.thermonitrificans was obtained after 48 h of incubation at 50°C. The pH and temperature optimafor proteolytic activity were 9.0 and 50°C, respectively. The proteolytic activity was stable at40°C for 1 h. The proteolytic activity was inhibited by DFP but not by EDTA or pCMB. Theseresults inidicated that the enzyme(s) can be classified as an alkaline protease. 1999 ElsevierScience Ltd. All rights reserved.     

Purification and characterization of a serine alkaline protease from Bacillus clausii GMBAE 42

An extracellular serine alkaline protease of Bacillus clausii GMBAE 42 was produced in protein-rich medium in shake-flask cultures for 3 days at pH 10.5 and 37°C. Highest alkaline protease activity was observed in the late stationary phase of cell cultivation. The enzyme was purified 16-fold from culture filtrate by DEAE-cellulose chromatography followed by (NH₄)₂SO₄ precipitation, with a yield of 58%. SDS-PAGE analysis revealed the molecular weight of the enzyme to be 26.50 kDa. The optimum temperature for enzyme activity was 60°C; however, it is shifted to 70°C after addition of 5 mM Ca²⁺ ions. The enzyme was stable between 30 and 40°C for 2 h at pH 10.5; only 14% activity loss was observed at 50°C. The optimal pH of the enzyme was 11.3. The enzyme was also stable in the pH 9.0–12.2 range for 24 h at 30°C; however, activity losses of 38% and 76% were observed at pH values of 12.7 and 13.0, respectively. The activation energy of Hammarsten casein hydrolysis by the purified enzyme was 10.59 kcal mol⁻¹ (44.30 kJ mol⁻¹). The enzyme was stable in the presence of the 1% (w/v) Tween-20, Tween-40,Tween-60, Tween-80, and 0.2% (w/v) SDS for 1 h at 30°C and pH 10.5. Only 10% activity loss was observed with 1% sodium perborate under the same conditions. The enzyme was not inhibited by iodoacetate, ethylacetimidate, phenylglyoxal, iodoacetimidate, n-ethylmaleimidate, n-bromosuccinimide, diethylpyrocarbonate or n-ethyl-5-phenyl-iso-xazolium-3′-sulfonate. Its complete inhibition by phenylmethanesulfonylfluoride and relatively high k _cat value for N-Suc-Ala-Ala-Pro-Phe-pNA hydrolysis indicates that the enzyme is a chymotrypsin-like serine protease. K _m and k _cat values were estimated at 0.655 μM N-Suc-Ala-Ala-Pro-Phe-pNA and 4.21×10³ min⁻¹, respectively.