Comparison of the specificities of various neutral proteinases from microorganisms

Feces Derived Allergens of Tyrophagus putrescentiae Reared on Dried Dog Food and Evidence of the Strong Nutritional Interaction between the Mite and Bacillus cereus Producing Protease Bacillolysins and Exo-chitinases

Tyrophagus putrescentiae (Schrank, 1781) is an emerging source of allergens in stored products and homes. Feces proteases are the major allergens of astigmatid mites (Acari: Acaridida). In addition, the mites are carriers of microorganisms and microbial adjuvant compounds that stimulate innate signaling pathways. We sought to analyze the mite feces proteome, proteolytic activities, and mite-bacterial interaction in dry dog food (DDF). Proteomic methods comprising enzymatic and zymographic analysis of proteases and 2D-E-MS/MS were performed. The highest protease activity was assigned to trypsin-like proteases; lower activity was assigned to chymotrypsin-like proteases, and the cysteine protease cathepsin B-like had very low activity. The 2D-E-MS/MS proteomic analysis identified mite trypsin allergen Tyr p3, fatty acid-binding protein Tyr p13 and putative mite allergens ferritin (Grp 30) and (poly)ubiquitins. Tyr p3 was detected at different positions of the 2D-E. It indicates presence of zymogen at basic pI, and mature-enzyme form and enzyme fragment at acidic pI. Bacillolysins (neutral and alkaline proteases) of Bacillus cereus symbiont can contribute to the protease activity of the mite extract. The bacterial exo-chitinases likely contribute to degradation of mite exuviae, mite bodies or food boluses consisting of chitin, including the peritrophic membrane. Thus, the chitinases disrupt the feces and facilitate release of the allergens. B. cereus was isolated and identified based on amplification and sequencing of 16S rRNA and motB genes. B. cereus was added into high-fat, high-protein (DDF) and low-fat, low-protein (flour) diets to 1 and 5% (w/w), and the diets palatability was evaluated in 21-day population growth test. The supplementation of diet with B. cereus significantly suppressed population growth and the suppressive effect was higher in the high-fat, high-protein diet than in the low-fat, low-protein food. Thus, B. cereus has to coexist with the mite in balance to be beneficial for the mite. The mite-B. cereus symbiosis can be beneficial-suppressive at some level. The results increase the veterinary and medical importance of the allergens detected in feces. The B. cereus enzymes/toxins are important components of mite allergens. The strong symbiotic association of T. putrescentiae with B. cereus in DDF was indicated.

Product inhibition in native-state proteolysis

The proteolysis kinetics of intact proteins by nonspecific proteases provides valuable information on transient partial unfolding of proteins under native conditions. Native-state proteolysis is an approach to utilize the proteolysis kinetics to assess the energetics of partial unfolding in a quantitative manner. In native-state proteolysis, folded proteins are incubated with nonspecific proteases, and the rate of proteolysis is determined from the disappearance of the intact protein. We report here that proteolysis of intact proteins by nonspecific proteases, thermolysin and subtilisin deviates from first-order kinetics. First-order kinetics has been assumed for the analysis of native-state proteolysis. By analyzing the kinetics of proteolysis with varying concentrations of substrate proteins and also with cleavage products, we found that the deviation from first-order kinetics results from product inhibition. A kinetic model including competitive product inhibition agrees well with the proteolysis time course and allows us to determine the uninhibited rate constant for proteolysis as well as the apparent inhibition constant. Our finding suggests that the likelihood of product inhibition must be considered for quantitative assessment of proteolysis kinetics.

Long-range stabilization of anthrax protective antigen upon binding to CMG2

Protective antigen (PA) mediates entry of edema factor (EF) and lethal factor (LF) into the cytoplasmic space of the cells through the formation of a membrane-spanning pore. To do this, PA must initially bind to a host cellular receptor. Recent mass spectrometry analysis of PA using histidine hydrogen–deuterium exchange (His-HDX) has shown that binding of the von Willebrand factor A (vWA) domain of the receptor capillary morphogenesis protein-2 (CMG2) lowers the exchange rates of the imidazole C₂ hydrogen of several histidines, suggesting that receptor binding decreases the structural flexibility of PA. Here, using His-HDX and fluorescence as a function of denaturant, and protease susceptibility, we show that binding of the vWA domain of CMG2 largely increases the stability of PA and the effect reaches up to 70 Å from the receptor binding interface. We also show that the pK_a values and HDX rates of histidines located in separate domains change upon receptor binding. These results indicate that when one end of the protein is anchored, the structure of PA is tightened, noncovalent interactions are strengthened, and the global stability of the protein increases. These findings suggest that CMG2 may be used to stabilize PA in future anthrax vaccines.

Identification of disulfide bonds in wheat gluten proteins by means of mass spectrometry/electron transfer dissociation

Disulfide bonds within gluten proteins play a key role in the breadmaking performance of wheat flour. In the present study, disulfide bonds of wheat gluten proteins were identified by using a new liquid chromatography-mass spectrometry (LC-MS) technique with alternating electron transfer dissociation (ETD)/collision-induced dissociation (CID). Wheat flour was partially hydrolyzed with thermolysin (pH 6.5, 37 °C, 16 h), and the digest was subjected to LC-MS with alternating ETD/CID fragmentation. Whereas CID provided peptide fragments with intact disulfide bonds, cleavage of disulfide bonds was preferred over peptide backbone fragmentations in ETD. The simultaneous observation of disulfide-linked and disulfide-cleaved peptide ions in the mass spectra not only provided distinct interpretation with high confidence but also simplified the conventional approach for determination of disulfide bonds, which often requires two separate experiments with and without chemical reduction. By application of the new method 14 cystine peptides were identified. Eight peptides confirmed previously established disulfide bonds within gluten proteins, and the other six cystine peptides were identified for the first time. One of the newly identified cystine peptides represented a "head-to-tail" cross-link between high molecular weight glutenin subunits. This type of cross-link, which has been postulated as an integral part of glutenin models published previously, has now been proven experimentally for the first time. From the six remaining cystine peptides interchain disulfide bonds between α-gliadins, γ-gliadins, and low molecular weight glutenin subunits were established.

Properties and substrate specificities of proteolytic enzymes from the edible basidiomycete Grifola frondosa

Highly active proteolytic enzymes are found in the fruiting bodies of Grifola frondosa. The general properties and substrate specificities of these proteases from G. frondosa (ProGF) were studied. The optimal pH for ProGF activity was pH 3 or 7 using hemoglobin or Hammersten casein as a substrate, respectively. The ProGF exhibited over 70% of maximal activity within the pH range of 4.5-8.5. In terms of temperature, the ProGF were maximally active at 55 degrees C, while over 80% of maximal activity was observed within the range of 50-75 degrees C. These proteases were substrate-specific, mainly cleaving at Ala(14)-Leu(15), Tyr(16)-Leu(17), and Pro(28)-Lys(29) bonds, with occasional cleavage of Phe(24)-Phe(25) bonds in the oxidized insulin B-chain. The ProGF also liberated hydrophobic amino acids, such as valine, leucine, and phenylalanine, using the oxidized insulin B-chain as a substrate. When soy protein was used as a substrate, valine, leucine, phenylalanine, and tyrosine were selectively released from the hydrolysate. Thus, over the time course of incubation, the peptide concentration increased as the average peptide chain length decreased. These results indicate that the ProGF include both endopeptidases recognizing leucine, phenylalanine, and lysine at the P1' position, and aminopeptidases preferentially releasing hydrophobic and aromatic amino acids such as valine, leucine, phenylalanine, and tyrosine.

Catalytic features of the botulinum neurotoxin A light chain revealed by high resolution structure of an inhibitory peptide complex

The Clostridium botulinum neurotoxin serotype A light chain (BoNT/A-LC) is a Zn(II)-dependent metalloprotease that blocks the release of acetylcholine at the neuromuscular junction by cleaving SNAP-25, one of the SNARE proteins required for exocytosis. Because of the potential for use of the toxin in bioterrorism and the increasingly widespread application of the toxin in the medical field, there is significant interest in the development of small-molecule inhibitors of the metalloprotease. Efforts to design such inhibitors have not benefited from knowledge of how peptides bind to the active site since the enzyme-peptide structures available previously either were not occupied in the vicinity of the catalytic Zn(II) ion or did not represent the product of SNAP-25 substrate cleavage. Herein we report the 1.4 A-resolution X-ray crystal structure of a complex between the BoNT/A-LC and the inhibitory peptide N-Ac-CRATKML, the first structure of the light chain with an inhibitory peptide bound at the catalytic Zn(II) ion. The peptide is bound with the Cys S gamma atom coordinating the metal ion. Surprisingly, the cysteine sulfur is oxidized to the sulfenic acid form. Given the unstable nature of this species in solution, is it likely that oxidation occurs on the enzyme. In addition to the peptide-bound structure, we report two structures of the unliganded light chain with and without the Zn(II) cofactor bound at 1.25 and 1.20 A resolution, respectively. The two structures are nearly identical, confirming that the Zn(II) ion plays a purely catalytic role. Additionally, the structure of the Zn(II)-bound uncomplexed enzyme allows identification of the catalytic water molecule and a second water molecule that occupies the same position as the peptidic oxygen in the tetrahedral intermediate. This observation suggests that the enzyme active site is prearranged to stabilize the tetrahedral intermediate of the protease reaction.

Enzyme-responsive hydrogel particles for the controlled release of proteins: designing peptide actuators to match payload

We report on enzyme-responsive hydrogel particles for the controlled release of proteins. Amino-functionalised poly(ethylene glycol acrylamide) (PEGA) hydrogel particles were functionalised with peptide actuators that cause charge-induced swelling and payload release when triggered enzymatically. Peptide-based actuators were designed to match the specificity of the target enzyme, while also matching the charge properties of the to-be released protein payload, thereby uniquely allowing for tuneable release profiles. Fluorescently labelled albumin and avidin, proteins of similar size but opposite charge, were released at a rate that was governed by the peptide actuator linked to the polymer carrier, offering a highly controlled release mechanism. Release profiles were analysed using a combination of fluorescence spectroscopy of the solution and two-photon fluorescence microscopy to analyse enzymatically triggered molecular events within hydrogel particles during the initial stages of release.

Purification, characterization cloning, and sequencing of metalloendopeptidase from Streptomyces septatus TH-2

Streptomyces septatus TH-2 secretes a large amount of a protease when cultured on a medium containing K(2)HPO(4) and glucose. The enzyme was purified to homogeneity by a three-step procedure. This enzyme had a molecular mass of approximately 35kDa, and was particularly inhibited by EDTA and phosphoramidon. Its substrate specificity was investigated using novel fluorescence energy transfer combinatorial libraries. The protease was found to prefer Phe and Tyr at the P(1) position, a hydrophobic or basic residue at the P(2) position, and a basic or small residue at the P(3) position. Its gene was cloned and sequenced, and its deduced amino acid sequence contained an HEXXH consensus sequence for zinc binding, confirming that it encodes metalloendopeptidase. The primary structure of the enzyme showed 40 and 69% identities with that of thermolysin from Bacillus thermoproteolyticus and that of a metalloendopeptidase from Streptomyces griseus, respectively.

Novel kinetic analysis of enzymatic dipeptide synthesis: effect of pH and substrates on thermolysin catalysis

The point of maximum activity is specific to a particular substrate-enzyme system but may vary with different substrates and the same enzyme. The specificity of enzymes has, however, been generally reported only at their "optimal" pH. In this article, we introduce the Michaelis-Menten equation taking pH into account, and apply it to the pH-activity profile of the thermolysin-catalyzed dipeptide synthesis. It has been reported to date that the pH-activity profile of thermolysin follows a bell-shaped curve with a maximal activity at or near pH 7.0. The profiles obtained in this study, however, indicated that the optimal pH varied from 5.8 (for F-AspPheOMe) to 7.3 (for Z-ArgPheOMe), and the order of thermolysin activity was greatly dependent on the pH of reaction media. We have succeeded in evaluating the substrates-induced change of the dissociation states of the active site of thermolysin using the hydrophobicity of substrates. We have obtained apparent kinetic parameters which are independent of the pH of reaction media. The apparent specificity of thermolysin which were independent of pH of the reaction media was in order L-Leu > L-Asp > L-Arg > L-Ala > L-Gly > L-Val and Z > Boc = F at P1 and P2 positions, respectively.

Purification of collagenase and specificity of its related enzyme from Bacillus subtilis FS-2

A collagenase in the culture supernatant of B. subtilis FS-2, isolated from traditional fish sauce, was purified. The enzyme had a molecular mass of about 125 kDa. It degraded gelatin with maximum activity at pH 9 and a temperature of 50 degrees C. The purified enzyme was stable over a wide range of pH (5-10) and lost only 15% and 35% activity after incubation at 60 degrees C and 65 degrees C for 30 min, respectively. Slightly inhibited by EDTA, soybean tripsin inhibitor, iodoacetamide, and iodoacetic acid, the enzyme was severely inhibited by 2-beta-mercaptoethanol and DFP. The protease from B. subtilis FS-2 culture digested acid casein into fragments with hydrophilic and hydrophobic amino acids as C-terminals, in particular Asn, Gly, Val, and Ile.

Activation and fragmentation of Bacillus thuringiensis delta-endotoxin by high concentrations of proteolytic enzymes

Commercial enzymes and insect gut juice at various concentrations were used to digest Bacillus thuringiensis subsp. sotto Cry1Aa protoxin and examine the fragmentation pattern and effect on insecticidal activity. Trypsin at both high (5 mg/mL) and low (0.05 mg/mL) concentrations converted protoxin to toxin with no difference in insecticidal activity against Bombyx mori larvae. In both cases, the toxin protein had an apparent M(r) of 58.4 kDa (SDS-PAGE). Active toxin of identical M(r) was also produced with low concentrations of Pronase and subtilisin, but at high concentration, it was degraded into two protease-resistant fragments of apparent M(r) 31.8 and 29.6 kDa, and exhibited no insecticidal activity. Sequencing data established the primary cleavage site to be in domain II, the receptor-binding region of the toxin, in an exposed loop between two beta-sheet strands. Fragmentation was not observed, however, when the digests were analyzed by native protein techniques, but rather the toxin molecule appeared to be intact. The amount of activated toxin produced by Choristoneura fumiferana gut juice was markedly reduced when the gut-juice concentration was increased from 1 to 50% and correlated with a loss in insecticidal activity. However, no lower M(r) protease-resistant fragments were evident in the SDS-PAGE of these digests.

Aspzincin, a family of metalloendopeptidases with a new zinc-binding motif. Identification of new zinc-binding sites (His(128), His(132), and Asp(164)) and three catalytically crucial residues (Glu(129), Asp(143), and Tyr(106)) of deuterolysin from Aspergillus oryzae by site-directed mutagenesis

Deuterolysin (EC 3.4.24.39; formerly designated as neutral proteinase II) from Aspergillus oryzae, which contains 1 g atom of zinc/mol of enzyme, is a single chain of 177 amino acid residues, includes three disulfide bonds, and has a molecular mass of 19,018 Da. Active-site determination of the recombinant enzyme expressed in Escherichia coli was performed by site-directed mutagenesis. Substitutions of His(128) and His(132) with Arg, of Glu(129) with Gln or Asp, of Asp(143) with Asn or Glu, of Asp(164) with Asn, and of Tyr(106) with Phe resulted in almost complete loss of the activity of the mutant enzymes. It can be concluded that His(128), His(132), and Asp(164) provide the Zn(2+) ligands of the enzyme according to a (65)Zn binding assay. Based on site-directed mutagenesis experiments, it was demonstrated that the three essential amino acid residues Glu(129), Asp(143), and Tyr(106) are catalytically crucial residues in the enzyme. Glu(129) may be implicated in a central role in the catalytic function. We conclude that deuterolysin is a member of a family of Zn(2+) metalloendopeptidases with a new zinc-binding motif, aspzincin, defined by the "HEXXH + D" motif and an aspartic acid as the third zinc ligand.

Substrate recognition and selectivity of peptide deformylase. Similarities and differences with metzincins and thermolysin

The substrate specificity of Escherichia coli peptide deformylase was investigated by measuring the efficiency of the enzyme to cleave formyl- peptides of the general formula Fo-Xaa-Yaa-NH2, where Xaa represents a set of 27 natural and unusual amino acids and Yaa corresponds to a set of 19 natural amino acids. Substrates with bulky hydrophobic side-chains at the P1' position were the most efficiently cleaved, with catalytic efficiencies greater by two to five orders of magnitude than those associated with polar or charged amino acid side-chains. Among hydrophobic side-chains, linear alkyl groups were preferred at the P1' position, as compared to aryl-alkyl side-chains. Interestingly, in the linear alkyl substituent series, with the exception of norleucine, deformylase exhibits a preference for the substrate containing Met in the P1' position. Next, the influence in catalysis of the second side-chain was studied after synthesis of 20 compounds of the formula Fo-Nle-Yaa-NH2. Their deformylation rates varied within a range of only one order of magnitude. A 3D model of the interaction of PDF with an inhibitor was then constructed and revealed indeed the occurrence of a deep and hydrophobic S1' pocket as well as the absence of a true S2' pocket. These analyses pointed out a set of possible interactions between deformylase and its substrates, which could be the ground driving substrate specificity. The validity of this enzyme:substrate docking was further probed with the help of a set of site-directed variants of the enzyme. From this, the importance of residues at the bottom of the S1' pocket (Ile128 and Leu125) as well as the hydrogen bond network that the main chain of the substrate makes with the enzyme were revealed. Based on the numerous homologies that deformylase displays with thermolysin and metzincins, a mechanism of enzyme:substrate recognition and hydrolysis could finally be proposed. Specific features of PDF with respect to other members of the enzymes with motif HEXXH are discussed.

Primary structure of Streptomyces griseus metalloendopeptidase II

Streptomyces griseus metalloendopeptidase II (SGMPII) is a unique protease, since it shows anomalous susceptibility to the proteinaceous "serine protease inhibitors" produced by Streptomyces, such as Streptomyces subtilisin inhibitor (SSI) and its homologous proteins. In this study, we analyzed the amino acid sequence of SGMPII by analyzing various peptide fragments produced enzymatically. The sequence of SGMPII, which is composed of 334 amino acids, showed no extensive similarity to SSI-insensitive metalloproteases produced by other species of Streptomyces, except for the amino acid residues essential for catalysis and zinc binding. However, SGMPII is 35-41% similar to thermolysin and its related metalloproteases, which are not inhibited by SSI, and the residues presumed to be critical for catalysis and zinc-binding are well conserved in SGMPII. Glu137 in a "His-Glu-Xaa-His" motif of SGMPII was identified as the residue modified by CICH2 CO-DL-(N-OH)Leu-Ala-Gly-NH2, an active-site-directed irreversible inhibitor of thermolysin-like metalloproteases. Based on the sequence comparison of SGMPII and other bacterial metalloproteases, we discuss the structural basis for the differences in substrate specificity and stability between SGMPII and other thermolysin-like proteases. A possible SSI-binding locus of SGMPII is also proposed.

A novel thermostable neutral proteinase from Saccharomonospora canescens

A novel thermostable neutral proteinase, called NPS, was purified to electrophoretic homogeneity from the culture broth of Saccharomonospora canescens sp. novus, strain 5. The molecular mass was determined by SDS-polyacrylamide gel electrophoresis to be 35,000 Da. The enzyme exhibits a sharp pH optimum of proteolytic activity at pH 6.7. NPS was completely inactivated with inhibitors, typical for metalloendopeptidases, EDTA and 1,10-phenantroline, whereas the serine proteinase inhibitor PMSF had no effect. Atomic absorption measurements showed that the proteinase binds a single zinc and four calcium ions. The enzyme thermostability was characterized in the absence and presence of added calcium. Melting temperature, Tm = 77 degrees C and an activation energy, Ea, for the thermal deactivation of the excited protein fluorophores of 72.13 kJ mol-1 were calculated in the presence of 100 mM CaCl2. The Ea-value is considerably higher than those obtained for a number of proteinases from microorganisms and was explained by the thermostable structure of the enzyme. Effective radiationless energy transfer from phenol groups to indole rings was observed. 68% of the light absorbed by tyrosyl residues is transferred to tryptophyl side chains. No homology was found after comparison of the NPS N-terminal sequence, including the first 26 residues, with those of other neutral proteinases from microorganisms. In contrast to the well-known bacterial neutral proteinase thermolysin and related enzymes from microorganisms, NPS possesses arylamidase and esterase activities. Further crystallographic studies will reveal the structural reasons for this specificity. Epoxy and epithio pyranosides are inhibitors of the proteinase arylamidase activity.

Elucidation of the thermal stability of the neutral proteinase II from Aspergillus oryzae

The neutral proteinase II from Aspergillus oryzae (NpII) is a zinc proteinase with three intramolecular disulfide bonds. NpII is most unstable after 10 min at about 75 degrees C, but regains stability beyond this temperature and is relatively stable at 100 degrees C. We analyzed the thermal stability of wild-type NpII and apo NpII. The results suggested that NpII unfolds reversibly upon incubation up to 100 degrees C, and that the irreversible inactivation observed is mainly due to autoproteolysis. To further understand the stability, a mutant NpII (Cys78-->Ala) lacking one of the disulfide bonds, was produced in a heterologous yeast expression system. The mutant NpII showed a similar stability profile, but the most unstable temperature and the most catalytically active temperature decreased to the same extent (around 10 degrees C), confirming that autoproteolysis is the main cause of the irreversible inactivation. Several lines of evidence presented in this study demonstrated that the thermal stability of o++NpII is attributed to reversible thermal unfolding and autoproteolysis.

Cloning and expression in yeast of a cDNA clone encoding Aspergillus oryzae neutral protease II, a unique metalloprotease

The neutral protease II (NpII) from Aspergillus oryzae is a zinc-containing metalloprotease with some unique properties. To elucidate its structure, we isolated a full-length cDNA clone for NpII. Sequence analysis reveals that NpII has a prepro region consisting of 175 amino acids preceding the mature region, which consists of 177 amino acids. As compared with other microbial metalloproteases, NpII is found to be unique in that it shares only a limited homology with them around two zinc ligand His residues and that the positions of the other zinc ligand (Glu) and the active site (His) cannot be established by homology. When a plasmid designed to express the prepro NpII cDNA was introduced into Saccharomyces cerevisiae and the transformant was cultured in YPD medium (2% glucose, 2% polypeptone, 1% yeast extract), it secreted a proNpII. However, in a culture of the same medium containing 0.2 mM ZnCl2, it secreted a mature NpII with a specific activity and N-terminus identical to those of native NpII. This observation suggests that either an autoproteolytic activity or a yeast protease effected the processing.

Purification and characterization of acidolysin, an acidic metalloprotease produced by Clostridium acetobutylicum ATCC 824

Acidolysin an extracellular protease produced by Clostridium acetobutylicum ATCC 824 was purified to homogeneity by anion-exchange chromatography with a recovery of 91%. The enzyme was a monomeric protein with a molecular weight of 44,000 as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and an acidic isoelectric point of 3.3. Acidolysin was very sensitive to metal-chelating agents and phosphoramidon and was unaffected by sulfhydryl reagents. It was shown to be a calcium- and zinc-containing protease. It exhibited optimal activity against Azocoll at pH 5 and 45 degrees C. It was stable at low pH and heat labile above 50 degrees C. It exhibited specificity toward peptide bonds formed by the amino group of hydrophobic amino acids (isoleucine, leucine, and phenylalanine) and its NH2-terminal amino acid sequence showed a high degree of similarity with that of Bacillus subtilis neutral metalloprotease A. Acidolysin is the first phosphoramidon-sensitive, acidic zinc metalloprotease reported.

Degradation of basement membranes by Pseudomonas aeruginosa elastase

Pseudomonas aeruginosa virulence has been attributed in part to extracellular proteinases. We found that one of these proteinases, elastase, extensively degrades intact basement membranes from bovine anterior-lens capsules, bovine glomeruli, and bovine lung, producing about 9, 14, and 9 fragments, respectively, with Mrs in the range of 15,000 to greater than 200,000, as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (nonreducing conditions). Release of hydroxyproline showed that collagen IV was degraded by elastase. Degradation of the newly discovered alpha 3(IV) collagen chain was shown by immunoblotting of digests with Goodpasture's syndrome serum, which contains antibodies that react with an epitope located in the carboxyl-terminal globular (NCl) domain of alpha 3(IV). Comparison of total protein release with collagen IV release showed that noncollagenous protein components were solubilized to the same extent as collagen IV. The extensive degradation of the basement membranes described here suggests a role for elastase in the pathogenic mechanism at the local level when P. aeruginosa infection is present.

Substrate inhibition of Pseudomonas aeruginosa elastase by 3-(2-furyl)acryloyl-glycyl-L-phenylalanyl-L-phenylalanine

The kinetics of hydrolysis by Pseudomonas aeruginosa elastase at 37 degrees C and pH 7.3 of 3-(2-furyl)acryloyl-glycyl-L-phenylalanyl-L-phenylalanine is compatible with nonproductive substrate inhibition, i.e., v = V.[S]/(Km + [S] + [S]2/K1), and the values of Km, Ki, and kappa cat are 1.4 mM, 5.0 mM, and 240 s-1, respectively. Product inhibition experiments are in agreement with an ordered release of product, with L-phenylalanyl-L-phenylalanine, the amino-containing product, being released first from the elastase.product complex. The values of Ki for L-phenylalanyl-L-phenylalanine and 3-(2-furyl)acryloyl-glycine are 1.5 and 4.0 mM, respectively. Kinetic experiments indicate that the second molecule of substrate combines with elastase.substrate to form a dead-end elastase . (substrate)2 complex.

Use of proline-specific endopeptidase in the isolation of all four "native" disulfides of hen egg white lysozyme

The disulfide peptides from the tryptic digestion of cyanogen bromide-treated hen egg white lysozyme (HEWL) were isolated by reverse phase high performance liquid chromatography (HPLC) and identified by amino acid analysis. Three peptides containing the I-VIII, II-VII, and III-V + IV-VI disulfide bonds were obtained. The two-disulfide peptide was further digested with proline-specific endopeptidase (PCE) (EC 3.4.21.26). Amino acid analysis of digest peptides separated by HPLC showed four peptides with the IV-VI disulfide bond as well as a peptide with the III-V disulfide bond. The IV-VI peptides were produced by hydrolysis of several alanine-X bonds as well as the prolyl-cystine bond. Our studies show that alanyl peptide bonds to lysyl, seryl, and leucyl residues are susceptible to hydrolysis by PCE preparations, thus substantially extending its known specificity range. The two-disulfide peptide was also digested sequentially with thermolysin and PCE; the resulting IV-VI and III-V peptides were identified by HPLC and amino acid analysis. PCE showed substantial activity at pH 5.3 as well as at pH 8.3. The lower pH is useful in studies of proteins or peptides where base-catalyzed reactions must be limited.

Proteinases of Pseudomonas aeruginosa evoke mucin release by tracheal epithelium

We have determined the potential of exoproducts from pathogenic bacteria to stimulate the release of high molecular weight mucins from goblet cells of airway epithelium in a rabbit tracheal explant system. Culture supernatants from proteolytic strains of Pseudomonas aeruginosa and Serratia marcescens, but not supernatants from a number of non-proteolytic strains, released mucins from goblet cells. Highly purified elastase and alkaline proteinase from P. aeruginosa stimulated goblet cell mucin release in a dose-dependent fashion. Lipopolysaccharide, exotoxin A, and alginate of P. aeruginosa did not possess mucin release properties. Proteolytic activity was required for mucin release by P. aeruginosa elastase, but such release in goblet cells was not mediated by cyclic AMP. Morphologic studies suggested rapid release of mucins from goblet cells was response to elastase by a process resembling apocrine secretion. Several nonbacterial proteinases mimicked the effect of Pseudomonas proteases. These studies provide support for the hypothesis that bacterial and other play a role in the pathogenesis of mucus hypersecretion in acute and chronic lung infections.

Proteolytic specificity of hemorrhage toxin a isolated from western diamondback rattlesnake (Crotalus atrox) venom

The proteolytic specificity of hemorrhagic toxin a from the venom of Crotalus atrox (western diamondback rattlesnake) has been investigated by using the oxidized B chain of bovine insulin and other peptides as substrates. The toxin appears highly specific for X--Leu bonds (cleaving the His10--Leu11, Ala14--Leu15, and Tyr16--Leu17 bonds), with no detectable activity against the Gly--Phe, Phe--Phe, Phe--Tyr, and Leu--Tyr bonds also present in the insulin B chain. The X--Leu bond of the peptides Tyr-Gly-Gly-Phe-Leu, Phe-Ala-Leu, and Ala-Leu was also cleaved. The toxin seems to be a strict endopeptidase, in that the cleavage of the two most susceptible bonds, Ala14--Leu15 and Tyr16--Leu17, are mutually exclusive; i.e., cleavage of either bond results in the other being too close to either the amino- or carboxyl-terminal of its respective fragment for the enzyme to be effective against it. The X--Met bond of Tyr-Gly-Gly-Phe-Met was cleaved, although a dipeptide Gly-Met was not hydrolyzed after 16 h of incubation. The substrates not hydrolyzed are furylacryloylglycyl-L-leucinamide, carbobenzoxy-L-glutamylglycine, carbobenzoxyglycyl-L-glutamic acid, benzoyl-L-arginine-p-nitroanilide, L-lysine-p-nitroanilide, (L-Ala)3-p-nitroanilide, Gly-Met, Gly-Phe-Phe, Gly-Gly-Ala, TAME, and ATEE. The absence of hydrolytic activity against the last two substrates indicates that hemorrhagic toxin a does not possess trypsin- or chymotrypsin-like activity.

Purification and properties of an extracellular protease from Myxococcus virescens

An extracellular protease from Myxococcus virescens was purified by phosphate precipitation, gel exclusion, and ion-exchange chromatography. The enzyme appeared homogeneous upon disc electrophoresis. The molecular weight of the protease was estimated to be 26,000. The enzyme was rapidly inactivated by ethylenediaminetetraacetate, but the activity could be partially restored by divalent cations. Diisopropylphosphorofluoridate inhibited enzyme activity completely. Michaelis-Menten kinetics were obeyed with casein and hemoglobin as substrates. First-order kinetics were obtained with elastin as the substrate, provided trypsin was in excess. Petidolytic activity indicated that the peptide bonds hydrolyzed by the enzyme were mainly those involving amino acids with nonpolar side chains.

Production and Purification of Thermostable Amylase and Protease of Thermomonospora viridis

Maximum yields of amylase were produced by the thermophilic actinomycete Thermomonospora viridis in a modified Simpson and McCoy medium containing 1.5% corn starch and 0.5% mycological peptone with an initial pH 7.0. Best yields of amylase were obtained after incubation for 48 h, when the pH of the medium had risen to 8.2. Amylase was purified 313-fold by precipitation with n -propyl alcohol, dialysis against tap water, adsorption on Ca 3 (PO 4 ) 2 , and fractionation on Sephadex G-100. Protease was produced in nutrient broth containing 0.5% starch and 1.0% corn steep liquor and at an initial pH 7.0. Maximum yields of protease were produced after 42 h. The protease was purified 54-fold by precipitation with n -propyl alcohol, dialysis against tap water, adsorption on Ca 3 (PO 4 ) 2 , and fractionation on Sephadex G-200.

Isolation of aminopeptidase from Aspergillus flavus

A mixture of aminopeptidase and neutral protease from the Aspergillus flavus mold obtained by chromatography on DEAE-Sephadex was fractionated by chromatography on the hydroxyalkyl methacrylate gel with chemically bonded 1,6 hexamethylene diamine and D-leucine. Aminopeptidase thus obtained was electrophoretically homogeneous. Conditions for chromatography were worked out allowing a one stage isolation of a highly active aminopeptidase sample directly from the alcoholic precipitate of the culture medium of the Aspergillus flavus mold.

Studies on the inhibition of thermolysin

Thei nhibition of the thermolysin catalyzed hydrolysis of FA-Gly-Leu-NH2 and FA-Gly-Phe-NH2 has been reported. The results suggest a model for substrate and inhibitor binding involving the hydrophobic specificity pocket, Arg-203 and Glu-143.