Characterization of the Denatured Structure of Pyrrolidone Carboxyl Peptidase from a Hyperthermophile under Nondenaturing Conditions: Role of the C-Terminal α-Helix of the Protein in Folding and Stability,

The cysteine-free pyrrolidone carboxyl peptidase (PCP-0SH) from a hyperthermophile, Pyrococcus furiosus, can be trapped in the denatured state under nondenaturing conditions, corresponding to the denatured structure that exists in equilibrium with the native state under physiological conditions. The denatured state is the initial state (D1 state) in the refolding process but differs from the completely denatured state (D2 state) in the concentrated denaturant. Also, it has been found that the D1 state corresponds to the heat-denatured state. To elucidate the structural basis of the D1 state, H/D exchange experiments with PCP-0SH were performed at pD 3.4 and 4 degrees C. The results indicated that amide protons in the C-terminal alpha6-helix region hardly exchanged in the D1 state with deuterium even after 7 days, suggesting that the alpha6-helix (from Ser188 to Glu205) of PCP-0SH was stably formed in the D1 state. In order to examine the role of the alpha6-helix in folding and stability, H/D exchange experiments with a mutant, A199P, at position 199 in the alpha6-helix region were performed. The alpha6-helix region of A199P in the D1 state was partially unprotected, while some hydrophobic residues were protected against the H/D exchange, although these hydrophobic residues were unprotected in the wild-type protein. These results suggest that the structure of A199P in the D1 state formed a temporary stable denatured structure with a non-native hydrophobic cluster and the unstructured alpha6-helix. Both the stability and the refolding rate decreased by the substitution of Pro for Ala199. We can conclude that the native-like helix (alpha6-helix) of PCP-0SH is already constructed in the D1 state and is necessary for efficient refolding into the native structure and stabilization of PCP-0SH.

Cloning and heterologous expression of bovine pyroglutamyl peptidase type-1 in Escherichia coli: purification, biochemical and kinetic characterisation

We describe the cloning, expression and purification of the bovine XM866409 form of pyroglutamyl peptidase type-1 (PAP1). The cloned nucleotide sequence has an ORF coding for a primary sequence of 209 amino acid residues, which displays 98% identity with the human AJ278828 form of the enzyme. Three amino acid residues at positions 81, 205 and 208 were found to vary between the two sequences. The recombinant bovine PAP1 with a C-terminal His(6) tag (rBtaPAP1(6H)) was expressed in Escherichia coli XL10-Gold cells and purified by immobilised nickel ion affinity chromatography resulting in a yield of 2.6 mg of PAP1 per litre of culture. Purified rBtaPAP1(6H) had a specific activity of 3633 units mg(-1). SDS-PAGE revealed a band for bovine PAP1 with a molecular weight of approximately 24 kDa, which is in good agreement with previously reported data on PAP1. The K (m) and k (cat) values obtained for rBtaPAP1(6H) were 59 muM and 3.5 s(-1), respectively. The optimum pH for activity was 9.0-9.5 and the optimum temperature was 37 degrees C. rBtaPAP1(6H) was found to have an absolute requirement for the thiol-reducing agent DTT, consistent with the expected property of a cysteine protease. Kinetic studies using the peptides pGlu-His-Pro-NH(2) (TRH), pGlu-Ala and pGlu-Val revealed K (i) values of 44.1, 141 and 652.17 microM, respectively. The lowest K (i), observed for Thyrotropin-releasing Hormone (TRH), indicates that rBtaPAP1(6H) has a higher affinity for tripeptides over dipeptides.

Differentiation of Leishmania major is impaired by over-expression of pyroglutamyl peptidase I

Pyroglutamyl peptidases I (PPI) are cysteine peptidases of the clan CF, family C15, which hydrolyse N-terminal l-pyroglutamyl residues (l-pGlu). The l-pGlu modification is a post-transcriptional modification that confers relative aminopeptidase resistance and, in some cases, is essential to the modified peptides' biological activity. PPIs have been identified in a variety of organisms, although definitive biological functions have yet to be attributed to them. The L. major PPI was expressed in Escherichia coli as active recombinant enzyme, and shown to have biochemical properties more similar to mammalian than bacterial PPIs. The LmPPI active site catalytic triad of E101, C210, and H234 was confirmed by mutagenesis. PPI activity was detected in L. major promastigotes, and the enzyme localised to the parasite cytosol. No detectable phenotype could be observed for L. major PPI-deficient mutants, which retained infectivity to macrophages in vitro and mice. However, over-expression of the active PPI, but not inactive PPI(C210A), in L. major impaired differentiation from the procyclic promastigote to the infective metacyclic promastigote. Susceptibility to a natural l-pGlu-modified antimicrobial peptide, gomesin, was tested using the different cell lines, which were all equally susceptible. Whilst PPI is widespread through the eukaryotic kingdom, this study now suggests that the enzyme is not essential for normal eukaryotic cell function. However, PPI could be involved in regulating the action of l-pGlu-modified peptides required for differentiation of L. major.

Pyroglutamyl peptidase type I from Trypanosoma brucei: a new virulence factor from African trypanosomes that de-blocks regulatory peptides in the plasma of infected hosts

Peptidases of parasitic protozoans are emerging as novel virulence factors and therapeutic targets in parasitic infections. A trypanosome-derived aminopeptidase that exclusively hydrolysed substrates with Glp (pyroglutamic acid) in P1 was purified 9248-fold from the plasma of rats infected with Trypanosoma brucei brucei. The enzyme responsible was cloned from a T. brucei brucei genomic DNA library and identified as type I PGP (pyroglutamyl peptidase), belonging to the C15 family of cysteine peptidases. We showed that PGP is expressed in all life cycle stages of T. brucei brucei and is expressed in four other blood-stream-form African trypanosomes. Trypanosome PGP was optimally active and stable at bloodstream pH, and was insensitive to host plasma cysteine peptidase inhibitors. Native purified and recombinant hyper-expressed trypanosome PGP removed the N-terminal Glp blocking groups from TRH (thyrotrophin-releasing hormone) and GnRH (gonadotropin-releasing hormone) with a k(cat)/K(m) value of 0.5 and 0.1 s(-1) x microM(-1) respectively. The half-life of TRH and GnRH was dramatically reduced in the plasma of trypanosome-infected rats, both in vitro and in vivo. Employing an activity-neutralizing anti-trypanosome PGP antibody, and pyroglutamyl diazomethyl ketone, a specific inhibitor of type I PGP, we demonstrated that trypanosome PGP is entirely responsible for the reduced plasma half-life of TRH, and partially responsible for the reduced plasma half-life of GnRH in a rodent model of African trypanosomiasis. The abnormal degradation of TRH and GnRH, and perhaps other neuropeptides N-terminally blocked with a pyroglutamyl moiety, by trypanosome PGP, may contribute to some of the endocrine lesions observed in African trypanosomiasis.

Genetic and functional analysis of pyroglutamyl-peptidase I in coeliac disease

Coeliac disease (CD) is an enteropathy caused by an immune reaction towards wheat gluten and similar proteins from barley and rye. It was shown that some gluten peptides spontaneously form N-terminal L-pyroglutamate. This modification could potentially make gluten more resistant to proteolytic degradation within the intestine. Pyroglutamyl-peptidase I (PGPEPI) is an enzyme that hydrolytically removes the L-pyroglutamyl residues that render the modified proteins and peptides more sensitive to degradation by other proteases. Interestingly, we found that the PGPEP1 gene is located in a CD susceptibility locus. As an impaired enzyme function caused by genetic alterations might increase the amount of immunogenic gluten peptides, we conducted a comprehensive functional genomics analysis of PGPEP1, including DNA sequencing, genetic association testing, and quantifying RNA expression. We also determined the enzymatic activity of PGPEPI in duodenal biopsies. Our results uniformly indicate that PGPEP1 is not involved in the aetiology and pathology of CD.

Unusually Slow Denaturation and Refolding Processes of Pyrrolidone Carboxyl Peptidase from a Hyperthermophile Are Highly Cooperative: Real-Time NMR Studies

The refolding rate of heat-denatured cysteine-free pyrrolidone carboxyl peptidase (PCP-0SH) from Pyrococcus furiosus has been reported to be unusually slow under some conditions. To elucidate the structural basis of the unusually slow kinetics of the protein, the denaturation and refolding processes of the PCP-0SH were investigated using a real-time 2D (1)H-(15)N HSQC and CD experiments. At 2 M urea denaturation of the PCP-0SH in the acidic region, all of the native peaks in the 2D HSQC spectrum completely disappeared. The conformation of the PCP-0SH just after removal of 6 M GuHCl could be observed as a stable intermediate (D(1) state) in 2D HSQC and CD experiments, which is similar to a molten globule structure. The D(1) state of the PCP-0SH, which is the initial state of refolding, corresponded to the state at 2 M urea and seemed to be the denatured state in equilibrium with the native state under the physiological conditions. The refolding of PCP-0SH from the D(1) state to the native state could be observed to be highly cooperative without any intermediates between them, even if the refolding rate was quite slow. In the higher concentration of denaturants, PCP-0SH showed HSQC and CD spectra characteristic of completely unfolded proteins called the D(2) state. The unusually slow refolding rate was discussed as originating in the conformations in the transition state and/or the retardation of reorganization in an ensemble of nonrandom denatured structures in the D(1) state.

Hydrolysis of synthetic substrate, L-pyroglutamyl p-nitroanilide is catalyzed solely by pyroglutamyl aminopeptidase I in rat liver cytosol

Pyroglutamyl aminopeptidase I (PAP-I) is a cytosolic cysteine peptidase, which hydrolytically removes the L-pyroglutamate residue from the amino terminus of endogenous proteins and peptides. L-Pyroglutamyl p-nitroanilide serves as the synthetic substrate of this enzyme, while there is a possibility of other hydrolases being involved in the hydrolysis of this xenobiotic substrate. We cloned a full-length cDNA encoding rat PAP-I from a rat liver cDNA library and expressed this cDNA in Escherichia coli to obtain a recombinant PAP-I as a single protein. The cDNA encoded a sequence of 209 amino acids with a calculated molecular weight of 22913 Da. The homology of the deduced amino acid sequence of rat PAP-I was 98.6 and 94.3% to mouse and human PAP-Is, respectively. The biochemical properties of the recombinant rat PAP-I were almost identical to those of the recombinant mouse and human PAP-Is and the purified rat liver cytosolic PAP-I in terms of the molecular weight, subunit structure, affinity to the substrate, inhibitor profile and pH optimum. Immunoblot analysis using an antibody raised against recombinant rat PAP-I showed that rat PAP-I is present almost exclusively in the cytosolic fraction of the rat liver. Moreover, the hydrolyzing activity for L-pyroglutamyl p-nitroanilide in rat liver cytosolic fraction was completely inhibited by the antibody, strongly suggesting that this xenobiotic substrate is hydrolyzed solely by PAP-I.

Pyroglutamyl-peptidase I: cloning, sequencing, and characterisation of the recombinant human enzyme

Pyroglutamyl-peptidase I (EC 3.4.19.3) is well known from bacteria and archaea, but has not previously been cloned or sequenced from any vertebrate. We describe the cloning and sequencing of the human (AJ278828) and mouse (AJ278829) forms of pyroglutamyl-peptidase I. The deduced amino acid sequences each consist of 209 residues and show approximately 30% identity with bacterial forms of the enzyme. They show clear homology to the enzyme from prokaryotes and place the mammalian forms of the enzyme in peptidase family C15 of the MEROPS database. The catalytic residues Glu81, Cys144, and His166 in the enzyme from Bacillus amyloliquefaciens are all conserved in the human sequence. A simple cartoon model of the human protein was constructed on the basis of the published crystal structures of pyroglutamyl-peptidase I forms from Thermococcus litoralis and B. amyloliquefaciens. The human enzyme was expressed by use of a baculovirus vector in Spodoptera frugiperda cells. The recombinant protein was enzymatically active and had properties similar to those described for the naturally occurring mammalian enzyme. Gel-filtration chromatography of the active enzyme gave a molecular mass of about 24kDa, showing that the enzyme is active as the monomer. This contrasted with indications that the prokaryotic enzymes may be tetrameric. Recombinant human pyroglutamyl-peptidase I was active on pGlu-aminomethylcoumarin in the range pH 6-9, with maximal activity being seen at pH 7.0-8.5; it showed an absolute requirement for a thiol-reducing agent. In crude preparations, the enzyme was completely stable for 90 min at 50 degrees C. The enzyme was inhibited by transition metal ions including Ni(2+), Zn(2+), and Cu(2+), and by sulfhydryl-blocking agents. Reversible inhibition was seen with 2-pyrrolidone (K(i)=50 microM), and surprisingly, with N-ethylmaleimide (K(i)=30 microM).

One step purification and characterization of the pyrrolidone carboxyl peptidase ofStreptococcus pyogenesover-expressed inEscherichia coli

Pyrrolidone carboxyl peptidase (EC 3.4.11.8) (Pcp), an enzyme which selectively removes pyrrolidone carboxylic acid (PCA) from some PCA-peptides and -proteins, was demonstrated in bacteria and in plant, animal and human tissues. In this paper we describe the purification to homogeneity of the enzyme of Streptococcus pyogenes, over-expressed in Escherichia coli. This was achieved, for the first time in one step, by hydrophobic interaction chromatography. Analysis under non-denaturing conditions revealed a molecular mass of 85 kDa and in the presence of sodium dodecyl sulfate gave a molecular mass of 23.5 kDa. Investigations on enzymatic properties showed that the Pcp over-expressed in E. coli disclosed properties similar to those found for the enzyme extracted from S. pyogenes or for some other Pcps studied previously. Thus the over-expressed enzyme should serve as a suitable source for N-terminal unblocking prior to some PCA protein sequencing.

Molecular cloning and characterization of Mycobacterium bovis BCG pcp gene encoding pyrrolidone carboxyl peptidase

The Mycobacterium bovis bacilli Calmette-Guerin (BCG) pcp gene that encodes the pyrrolidone carboxyl peptidase (Pcp) was cloned from a lambdagtll genomic library and sequenced. The nucleotide sequence contains a 669 bp open reading frame coding for a protein of 222 amino acid residues with a calculated molecular mass of 23,209 Da. The deduced amino acid sequence is highly homologous to the Pcps from Bacillus amyloliquefaciens, Pseudomonas fluorescens, Bacillus subtilis, Streptococcus pyogenes, and Staphylococcus aureus. A multiple sequence alignment revealed highly conserved domains. The BCG pcp gene was overexpressed in Escherichia coli. The Pcp was purified to homogeneity. The recombinant protein was further confirmed by an enzymatic assay.

X-ray crystalline structures of pyrrolidone carboxyl peptidase from a hyperthermophile, Pyrococcus furiosus, and its cys-free mutant

In order to elucidate the mechanism of the thermostability of proteins from hyperthermophiles, X-ray crystalline structures of pyrrolidone carboxyl peptidase from a hyperthermophile, Pyrococcus furiosus (PfPCP), and its mutant protein with Ser substituted at Cys142 and Cys188 were determined at 2.2 and 2.7 A resolution, respectively. The obtained structures were compared with those previously reported for pyrrolidone carboxyl peptidases from a hyperthermophilie, Thermococcus litoralis (TlPCP), and from a mesophile, Bacillus amyloliquefaciens (BaPCP). The PfPCP structure is a tetramer of four identical subunits similar to that of the TlPCP and BaPCP. The largest structural changes among the three PCPs were detected in the C-terminal protrusion, which interacts with that of another subunit. A comparison of the three structures indicated that the high stability of PfPCP is caused by increases in hydrophobic interactions and hydrogen bonds, the formation of an intersubunit ion-pair network, and improvement to an ideal conformation. On the basis of the structures of the three proteins, it can be concluded that PfPCP does not have any special factors responsible for its extremely high stability and that the conformational structure of PfPCP is superior in its combination of positive and negative stabilizing factors compared with BaPCP.

The mechanism of aubstrate eecognition of pyroglutamyl-peptidase I from Bacillus amyloliquefaciens as determined by X-ray crystallography and site-directed mutagenesis

Pyroglutamyl-peptidase is able to specifically remove the amino-terminal pyroglutamyl residue protecting proteins or peptides from aminopeptidases. To clarify the mechanism of substrate recognition for the unique structure of the pyrrolidone ring, x-ray crystallography and site-directed mutagenesis were applied. The crystal structure of pyroglutamyl-peptidase bound to a transition state analog inhibitor (Inh), pyroglutaminal, was determined. Two hydrogen bonds were located between the main chain of the enzyme and the inhibitor (71:O.H-N:Inh and Gln71:N-H.OE:Inh), and the pyrrolidone ring of the inhibitor was inserted into the hydrophobic pocket composed of Phe-10, Phe-13, Thr-45, Ile-92, Phe-142, and Val-143. To study in detail the hydrophobic pocket, Phe-10, Phe-13, and Phe-142 were selected for mutation experiments. The k(cat) value of the F10Y mutant decreased, but the two phenylalanine mutants F13Y and F142Y did not exhibit significant changes in kinetic parameters compared with the wild-type enzyme. The catalytic efficiencies (k(cat)/K(m)) for the F13A and F142A mutants were less than 1000-fold that of the wild-type enzyme. The x-ray crystallographic study of the F142A mutant showed no significant change except for a minor one in the hydrophobic pocket compared with the wild type. These findings indicate that the molecular recognition of pyroglutamic acid is achieved through two hydrogen bonds and an insertion in the hydrophobic pocket. In the pocket, Phe-10 is more important to the hydrophobic interaction than is Phe-142, and furthermore Phe-13 serves as an "induced fit" mechanism.

Cloning, expression, and characterization of pyrrolidone carboxyl peptidase from the archaeon Thermococcus litoralis

The gene encoding pyrrolidone carboxyl peptidase (Pcp) has been cloned from the hyperthermophilic archaeon Thermococcus litoralis. The recombinant enzyme has been expressed in Escherichia coli, purified, and characterized. The T. litoralis Pcp demonstrates strong sequence homology to previously characterized bacterial Pcps. Some investigations have been carried out on enzyme substrate specificity and stability.

Pyroglutamyl peptidase: an overview of the three known enzymatic forms

Pyroglutamyl peptidase can be classified as an omega peptidase which hydrolytically removes the amino terminal pyroglutamate (pGlu) residue from specific pyroglutamyl substrates. To date, three distinct forms of this enzyme have been identified in mammalian tissues. Type I is typically a cytosolic, cysteine peptidase displaying a broad pyroglutamyl substrate specificity and low molecular mass. Type II has been shown to be a membrane anchored metalloenzyme of high molecular mass with a narrow substrate specificity restricted to the hypothalamic releasing factor, thyrotropin-releasing hormone (TRH, pGlu-His-Pro-NH2). A third pyroglutamyl peptidase activity has also been observed in mammalian serum which displays biochemical characteristics remarkably similar to those of tissue Type II, namely a high molecular mass, sensitivity to metal chelating agents, and a narrow substrate specificity also restricted to TRH. This serum activity has subsequently been designated 'thyroliberinase'. This review surveys the biochemical, enzymatic, and structural properties of this interesting and unique class of peptidases. It also addresses the putative physiological roles which have been ascribed to these enzymes. Pyroglutamyl peptidase activities isolated and characterized from bacterial sources are also reviewed and compared with their mammalian counterparts.

Pyrrolidone carboxyl peptidase from the hyperthermophilic Archaeon Pyrococcus furiosus: cloning and overexpression in Escherichia coli of the gene, and its application to protein sequence analysis

A gene for a pyrrolidone carboxyl peptidase (Pcp: EC 3.4.19.3, pyroglutamyl peptidase), which removes amino-terminal pyroglutamyl residues from peptides and proteins, has been cloned from the hyperthermophilic Archaeon Pyrococcus furiosus using its cosmid protein library, sequenced, and expressed in Escherichia coli. The DNA sequence encodes a protein containing 208 amino acid residues with methionine at the N-terminus. Analysis of the recombinant protein expressed in E. coli, including amino acid sequence analysis from the N-terminus by automated Edman degradation and ionspray mass spectrometric analysis of the peptides generated by enzymatic digestions with lysylendopeptidase and Staphylococcus aureus V8 protease, showed its primary structure to be completely identical with that deduced from its cDNA sequence. Comparison of the amino acid sequence of P. furiosus Pcp (P.f.Pcp) with those of bacterial Pcps revealed that a high degree of sequence identity (more than 40%) and conservation of the amino acid residues comprising the catalytic triad, Cys142, His166, and Glu79. On the other hand, a unique short stretch sequence (positions around 175-185) that is absent in bacterial Pcps was found in P.f.Pcp. A similar stretch has also been reported recently in the amino acid sequence of Pcp from the hyperthermophilic Archaeon Thermococcus litoralis [Littlechild et al., in abstracts of the "International Congress on Exthermophiles '98" p. 58 (1998)]. To elucidate their contribution to the hyperthermostability of these enzymes, further structural studies are required.

Pyroglutamic acid and iron regulate the expression of the pcp gene in Pseudomonas fluorescens MFO

Pyrrolidone carboxyl peptidase (Pcp) is an aminopeptidase (EC 3.4.11.8) able to specifically remove the L-pyroglutamyl residue from the amino-terminus of polypeptides. Since nothing was known concerning the regulation and function of Pcps, a mutant of a milk-isolated strain lacking Pcp activity (Pseudomonas fluorescens MB1), was constructed by homologous recombination using a transcriptional fusion between pcp and a reporter gene (uidA). The wild-type and mutant strains were grown in synthetic media and in milk to investigate the environmental effects on pcp transcription. The expression of pcp and of the transcriptional fusion pcp::uidA was not sensitive to environmental conditions like temperature, osmolarity or nitrogen and phosphate starvation but was induced by the product of the enzymatic activity, pyroglutamic acid (pGlu). The expression of the native gene and the fusion in inducing conditions was also controlled by the iron concentration. The identification in the pcp promoter sequence of putative ferric uptake regulator (Fur) binding sites suggests a transcriptional regulation in a Fur-dependent fashion. Two other putative regulatory stretches, corresponding to inverted repeated sequences with perfect and imperfect symmetry, were also identified. pGlu and iron are therefore at least two of the transcriptional effectors of pcp expression.

The biosynthetic incorporation of selenomethionine and telluromethionine into pyrrolidone carboxyl peptidase (PYRase) from S. aureus

Heavy-atom derivatives of PYRase proteins prepared in the past have been unsuitable for x-ray diffraction analysis. Thus, we propose utilizing unnatural metalloid-containing amino acids as an alternative to heavy-atom derivatization. Selenomethionine-containing proteins analyzed by multiwavelength anomalous diffraction provides a facile means of addressing the phase problem, whose solution is necessary to determine protein structures by X-ray Crystallography [Hendrickson, et al., 1991 and references therein]. Telluromethionine-containing proteins offer the same investigational potential, and additionally allow further simplification of the data collection technique by requiring only traditional methods of phase analysis [Boles et al., 1995 and references therein]. We sought to introduce the required Se and Te atoms into Staphylococcus aureus Pyrrolidone Carboxyl Peptidase (PYRase) via selenomethionine (SeMet) and telluromethionine (TeMet). Complete incorporation of SeMet into S. aureus PYRase was succeeded with little change in enzymatic properties. Incomplete incorporation (75%) of TeMet was accomplished in preparing TeMet-PYRase, however, representing the highest incorporation to date of a tellurium-containing amino acid. Enzymatic properties remained unchanged when TeMet was incorporated. We report herein the biosynthetic substitution and expression, protein purification and comparative biochemistry of SeMet-PYRase and TeMet-PYRase.

Isolation and characterization of pcp, a gene encoding a pyrrolidone carboxyl peptidase in Staphylococcus aureus

The pcp gene, encoding a pyrrolidone carboxyl peptidase (PYRase), was cloned from a lambda GT11 genomic library prepared from Staphylococcus aureus FDA 574 and sequenced. The pcp gene is located 740 bp downstream from cna, a gene that encodes a collagen-binding adhesin in S. aureus. S. aureus pcp encodes a 212-amino-acid (aa) polypeptide. The pcp gene was overexpressed in Escherichia coli and the PYRase purified to homogeneity. The recombinant enzyme exhibited biological activity, as determined using the chromogenic substrate L-pyroglutamyl-beta-napthylamide. Biochemical analysis of the PYRase using thiol-blocking chemicals suggested that the enzyme belongs to the cysteine peptidase family. Moreover, multiple sequence alignment revealed a high degree of similarity to previously described bacterial PYRases. This family of peptidases has been used to selectively remove the N-terminal pyrrolidone carboxylic acid residue found on certain blocked proteins and peptides prior to aa sequencing. However, the exact biological role of PYRases has yet to be elucidated.

Pyrrolidone carboxyl peptidase (Pcp): an enzyme that removes pyroglutamic acid (pGlu) from pGlu-peptides and pGlu-proteins

Pyrrolidone carboxyl peptidase (EC 3.4.11.8) is an exopeptidase commonly called PYRase, which hydrolytically removes the pGlu-proteins. pGlu also known as pyrrolidone carboxylic acid may occur naturally by an enzymatic procedure or may occur as an artifact in proteins or peptides. The enzymatic synthesis of pGlu suggests that this residue may have important biological and physiological functions. Several studies are consistent with this supposition. PYRase has been found in a variety of bacteria, and in plant, animal, and human tissues. For over two decades, biochemical and enzymatic properties of PYRase have been investigated. At least two classes of PYRase have been characterized. The first one includes the bacterial and animal type I PYRases and the second one the animal type II and serum PYRases. Enzymes from these two classes present differences in their molecular weight and in their enzymatic properties. Recently, the genes of PYRases from four bacteria have been cloned and characterized, allowing the study of the primary structure of these enzymes, and their over-expression in heterelogous organisms. Comparison of the primary structure of these enzymes revealed striking homologies. Type I PYRases and bacterial PYRases are generally soluble enzymes, whereas type II PYRases are membrane-bound enzymes. PYRase II appears to play as important a physiological role as other neuropeptide degrading enzymes. However, the role of type I and bacterial PYRases remains unclear. The primary application of PYRase has been its utilization for some protein or peptide sequencing. Development of chromogenic substrates for this enzyme has allowed its use in bacterial diagnosis.

Characterization of the pcp gene of Pseudomonas fluorescens and of its product, pyrrolidone carboxyl peptidase (Pcp)

The gene pcp, encoding pyrrolidone carboxyl peptidase (Pcp), from Pseudomonas fluorescens MFO was cloned and its nucleotide sequence was determined. This sequence contains a unique open reading frame (pcp) coding for a polypeptide of 213 amino acids (M(r) 22,441) which has significant homology to the Pcps from Streptococcus pyogenes, Bacillus subtilis, and Bacillus amyloliquefaciens. Comparison of the four Pcp sequences revealed two highly conserved motifs which may be involved in the active site of these enzymes. The cloned Pcp from P. fluorescens was purified to homogeneity and appears to exist as a dimer. This enzyme displays a Michaelis constant of 0.21 mM with L-pyroglutamyl-beta-naphthylamide as the substrate and an absolute substrate specificity towards N-terminal pyroglutamyl residues. Studies of inhibition by chemical compounds revealed that the cysteine and histidine residues are essential for enzyme activity. From their conservation in the four enzyme sequences, the Cys-144 and His-166 amino acids are proposed to form a part of the active site of these enzymes.

Pyroglutamyl peptidase gene from Bacillus amyloliquefaciens: cloning, sequencing, expression, and crystallization of the expressed enzyme

The pyroglutamyl peptidase [EC 3.4.11.8] gene from Bacillus amyloliquefaciens was cloned and expressed in Escherichia coli DH1. The transformant of E. coli DH1 harboring plasmid pBPG 1 with a 2.1 kb chromosomal DNA fragment showed 80-fold higher activity than B. amyloliquefaciens. The nucleotide sequence of a 0.9 kb fragment that contains the promoter and the mature protein coding region was determined by the dideoxy chain-termination method. An open reading frame of 648 bp starting with an ATG methionine codon was found, which encodes a protein of 215 amino acid residues with a deduced molecular weight of 23,286. The enzyme has two cysteine residues (Cys68 and Cys144) per subunit molecule. Substitution of Cys144 with Ser by site-directed mutagenesis resulted in a complete loss of the activity, while that of Cys68 with Ser did not affect the activity at all. This result and titration with DTNB suggest that Cys144 is concerned in the catalytic action and Cys68 is located inside the enzyme. The expressed enzyme was purified to homogeneity by hydrophobic chromatography on a Toyopearl HW-65C column and crystallization, with an activity recovery of 42.7%. The enzyme was most active at pH 6.5 and stable at pH 7.0-9.0. Its molecular weight was estimated to be 51,000 by gel filtration, suggesting it to be a dimer. Big crystals of the wild and PCMB-modified enzymes were obtained by the hanging drop method.

Characterization of the pcp gene encoding the pyrrolidone carboxyl peptidase of Bacillus subtilis

Pyrrolidone carboxyl peptidase (EC 3.4.11.8) (Pcp) is an enzyme that catalyzes the removal of the N-terminal pyroglutamyl group from some peptides or proteins. Its value in protein chemistry and bacterial diagnosis makes this enzyme an interesting subject of study. The present paper reports for the first time the cloning and characterization of a pyrrolidone carboxyl peptidase gene (pcp). This gene is present in a single copy in the genome of Bacillus subtilis as indicated by Southern blot hybridization analysis. The pcp transcripts were analyzed in Escherichia coli by Northern blot hybridization and S1 nuclease mapping. The deduced amino acid sequence predicts a protein of 215 amino acids with a calculated molecular weight of 23,777 Da. The pcp gene has been over-expressed in E. coli, allowing the identification and partial characterization of Pcp protein.

Molecular characterization of pcp, the structural gene encoding the pyrrolidone carboxylyl peptidase from Streptococcus pyogenes

This paper describes the cloning of a gene (pcp) coding for pyrrolidone carboxylyl peptidase (PYRase), an enzyme which selectively removes N-terminal pyroglutamic acid residues from polypeptides. This gene was isolated from Streptococcus pyogenes by construction of a gene library with a bacteriophage lambda-derived cosmid-Escherichia coli host system. Nucleotide sequence determination of a 1.3 kb restriction fragment revealed a 645 bp open reading frame encoding a 215-amino-acid product of M(r) 23,135 consistent with the 26 kDa polypeptide obtained from in vivo overexpression in E. coli. Southern hybridization confirmed that pcp is a single-copy gene on the S. pyogenes chromosome. 5' and 3' endpoint mapping of the 0.7 kb specific transcript observed by Northern analysis permitted the identification of transcriptional initiation and termination signals. Structural features of the pcp gene product from S. pyogenes are discussed and compared with that from Bacillus subtilis. The lack of sequence identity with any other known protein or nucleotide sequence suggests that this enzyme belongs to a new class of peptidase.