Human kidney prolidase--purification, preincubation properties and immunological reactivity

Trichomonas vaginalis metalloproteinase TvMP50 is a monomeric Aminopeptidase P-like enzyme

Previously, metalloproteinase was isolated and identified from Trichomonas vaginalis, belonging to the aminopeptidase P-like metalloproteinase subfamily A/B, family M24 of clan MG, named TvMP50. The native and recombinant TvMP50 showed proteolytic activity, determined by gelatin zymogram, and a 50 kDa band, suggesting that TvMP50 is a monomeric active enzyme. This was an unexpected finding since other Xaa-Pro aminopeptidases/prolidases are active as a biological unit formed by dimers/tetramers. In this study, the evolutionary history of TvMP50 and the preliminary crystal structure of the recombinant enzyme determined at 3.4 Å resolution is reported. TvMP50 was shown to be a type of putative, eukaryotic, monomeric aminopeptidase P, and the crystallographic coordinates showed a monomer on a "pseudo-homodimer" array on the asymmetric unit that resembles the quaternary structure of the M24B dimeric family and suggests a homodimeric aminopeptidase P-like enzyme as a likely ancestor. Interestingly, TvMP50 had a modified N-terminal region compared with other Xaa-Pro aminopeptidases/prolidases with three-dimensional structures; however, the formation of the standard dimer is structurally unstable in aqueous solution, and a comparably reduced number of hydrogen bridges and lack of saline bridges were found between subunits A/B, which could explain why TvMP50 portrays monomeric functionality. Additionally, we found that the Parabasalia group contains two protein lineages with a "pita bread" fold; the ancestral monomeric group 1 was probably derived from an ancestral dimeric aminopeptidase P-type enzyme, and group 2 has a probable dimeric kind of ancestral eukaryotic prolidase lineage. The implications of such hypotheses are also presented.

The relationships among the levels of oxidative and antioxidative parameters, FEV1 and prolidase activity in COPD

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) is a progressive condition characterized by poorly reversible airflow limitations associated with an abnormal inflammatory response of the lung.

METHODS

We investigated whether prolidase levels in serum, total antioxidant status, total oxidative status (TOS), and the oxidative stress index (OSI) were associated with the etiopathogenesis of COPD, and whether there is a relationship between prolidase activity and oxidative parameters and carotid artery intima-media thickness (CIMT) in patients with COPD. This study included 91 patients with COPD and 15 control cases. Routine haematological and biochemical parameters were determined in all patients. All subjects were fully informed about the study and provided consent.

RESULTS

The mean age of the patients with COPD was 61.3 ± 10.5 years and that of the control group was 56.2 ± 12.1 years. The control group had a significantly higher plasma prolidase level than that in the COPD group. TOS and OSI levels in the control group were significantly lower than those in the COPD group. However, no significant differences were found in TALs or CIMT levels between the COPD and control groups. A negative correlation was detected between prolidase activity and age; however, no significant difference in age was observed between the two groups.

CONCLUSION

These results indicate that prolidase activity decreases in patients with COPD.

Prolidase activity dysregulation and its correlation with oxidative-antioxidative status in chronic obstructive pulmonary disease

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a consequence of an underlying chronic inflammatory disorder of the airways that is usually progressive and causes dysregulation in the metabolism of collagen. Prolidase has an important role in the recycling of proline for collagen synthesis and cell growth.

OBJECTIVE

We measured and compared prolidase activity in healthy individuals with COPD patients to find out that whether its activity might reflect disturbances of collagen metabolism in the patients. We also investigated oxidative-antioxidative status and its relationship with prolidase activity in this disease.

METHODS

Thirty voluntary patients with COPD and 30 healthy control subjects with similar age range and sex were included into the study. Plasma prolidase activities, total antioxidant capacity (TAC) and lipid peroxidation (LPO) levels were measured in the patient and control groups.

RESULTS

Plasma prolidase activity and TAC levels were significantly lower, and LPO levels were significantly higher in the patients than those in the control subjects (P<0.05, P<0.001, and P<0.001, respectively). Significant correlations were detected between plasma prolidase activity and TAC and LPO levels in the patients group (r=0.679, P<0.001; r=-426, P<0.05, respectively).

CONCLUSIONS

The results suggest that oxidative-antioxidative balance and collagen turnover are altered by the development of COPD in human lungs, and prolidase activity may reflect disturbances of collagen metabolism in this pulmonary disease. Monitoring of plasma prolidase activity and oxidative-antioxidative balance may be useful in evaluating fibrotic processes and oxidative damage in the chronic inflammatory lung disease in human.

Metalloproteases and Proteolytic Processing

Proteolytic enzymes constitute around 2% of the human genome and are involved in all stages of cell and organism development from fertilization through to cell death. In the human genome the major classes of peptidases are represented by cysteine-, serine- and metalloenzymes, which possess a wide spectrum of substrate specificity and physiological functions. The identification of many novel peptidases from genome sequencing programmes has suggested potential new therapeutic targets. In addition, several well characterised peptidases were recently shown to possess new and unexpected biological roles in neuroinflammation, cancer and angiogenesis, cardiovascular diseases and neurodegeneration. This chapter will briefly characterize the main classes of metallopeptidases and their roles in health and disease. Particular attention will be paid to the angiotensin-converting enzyme (ACE), neprilysin (NEP) and adamalysin (ADAM) families of proteases and their pathophysiological roles with a particular emphasis on cancer and neurodegeneration. The roles and mechanisms of protein shedding which primarily involve the ADAMs family of metallopeptidases will be explained using amyloid protein precursor (APP) processing cascades as a well characterized example. The therapeutic significance of modulating (activating or inhibiting) metallopeptidase activity will be a particular focus of this chapter.

Acute effect of phosphodiesterase type 5 inhibitor on serum oxidative status and prolidase activities in men with erectile dysfunction

OBJECTIVES

To investigate the acute effect of phosphodiesterase type 5 (PDE5) inhibitor on erectile dysfunction by evaluating serum oxidative status and prolidase activity.

METHODS

Serum samples of 36 patients with erectile dysfunction and 30 control cases were analyzed for total antioxidant status, total oxidant status, and prolidase activity, before and after the administration of tadalafil citrate.

RESULTS

Before and after tadalafil citrate administration, serum total antioxidant status, total oxidant status, and prolidase were 1.1+0.0 vs. 1.6 + 0.0 umol H₂O₂ Eq/L, 10.3+1.1 vs. 6.9 + 1.2 umol H₂O₂ Eq/L, and 236.4+19.5 vs. 228.2 + 19.2 U/L, respectively (p < 0.0001 for all).

CONCLUSIONS

Evaluation of serum oxidative status and prolidase activity confirmed the beneficial acute effects of PDE5 inhibitor in patients with erectile dysfunction.

S1 site residues of Lactococcus lactis prolidase affect substrate specificity and allosteric behaviour

Lactococcus lactis prolidase preferably hydrolyzes Xaa-Pro dipeptides where Xaa is a hydrophobic amino acid. Anionic Glu-Pro and Asp-Pro dipeptides cannot be hydrolyzed at any observable rates and the hydrolysis of cationic Arg-Pro and Lys-Pro dipeptides is at about one tenth of the rate of Leu-Pro. It was hypothesized that the hydrophobic residues in the S1 site were responsible for this substrate specificity, thus the residues in the S1 site were substituted with hydrophilic residues. The substitution of Leu193 and Val302 revealed that these residues influenced the substrate specificity. The introduction of a cationic residue, L193R, allowed Asp-Pro to be utilized as a substrate at 37.0% of the rate of Leu-Pro, and the anionic mutation, V302D, yielded mutants that could hydrolyze Asp-Pro, Arg-Pro and Lys-Pro at 25.9 to 57.4% rates. Interestingly, these mutants of S1 site residues eliminated the allosteric behaviour of L. lactis prolidase that makes this enzyme unique among known prolidases. Results of pH dependency, thermal dependency, and molecular modelling suggested that these observed changes were due to the alteration of the interactions among catalytic zinc cations, Arg293, His296, and the mutated residues.

Biotechnological applications of recombinant microbial prolidases

Prolidase is a metallopeptidase that is ubiquitous in nature and has been isolated from mammals, bacteria and archaea. Prolidase specifically hydrolyzes dipeptides with a prolyl residue in the carboxy terminus (NH(2)-X-/-Pro-COOH). Currently, the only solved structure of prolidase is from the hyperthermophilic archaeon Pyrococcus furiosus. This enzyme is of particular interest because it can be used in many biotechnological applications. Prolidase is able to degrade toxic organophosphorus (OP) compounds, namely, by cleaving the P-F and P-O bonds in the nerve agents, sarin and soman. Applications using prolidase to detoxify OP nerve agents include its incorporation into fire-fighting foams and as biosensors for OP compound detection. Prolidases are also employed in the cheese-ripening process to improve cheese taste and texture. In humans, prolidase deficiency (PD) is a rare autosomal recessive disorder that affects the connective tissue. Symptoms of PD include skin lesions, mental retardation and recurrent respiratory infections. Enzyme replacement therapies are currently being studied in an effort to optimize enzyme delivery and stability for this application. Previously, prolidase has been linked to collagen metabolism and more recently is being associated with melanoma. Increased prolidase activity in melanoma cell lines has lead investigators to create cancer prodrugs targeting this enzyme. Thus, there are many biotechnological applications using recombinant and native forms of prolidase and this review will describe the biochemical and structural properties of prolidases as well as discuss their most current applications.

Prolidase isoenzymes in the rat: their organ distribution, developmental change and specific inhibitors

Lack of prolidase I (PD I) leads to prolidase deficiency, a disease characterized by intractable skin lesions, recurrent respiratory infections, and mental retardation. The present study was undertaken to characterize and determine the physiologic roles of different prolidase isoenzymes. Two isoforms of prolidase were isolated from rat kidney. PD I showed higher activity against seryl-proline and alanyl-proline, whereas PD II was active especially against methionyl-proline. PD I was highly concentrated in the small intestine and kidney, whereas PD II was shown not to vary in the organs examined. Expression of PD I and PD II in the small intestine were maximal within 1 wk of birth, and then rapidly declined. The changes of prolidase in the kidney and heart were found to differ slightly. N-benzyloxycarbonyl-l-proline and captopril inhibited PD I dose-dependently, but showed no inhibition of PD II at low concentrations. NiCl2 inhibited PD II much more effectively than PD I. Our findings suggest that PD I functions by way of an intestinal peptide carrier, which may also be regulated by the uptake of various iminodipeptides. Similarly, age-related alterations of prolidase isoenzymes suggest that intestinal PD II also participates in absorption of proline and other amino acids early in life.

Proline Prodrug of Melphalan Targeted to Prolidase, a Prodrug Activating Enzyme Overexpressed in Melanoma

PURPOSE

To determine the bioactivation and uptake of prolidase-targeted proline prodrugs of melphalan in six cancer cell lines with variable prolidase expression and to evaluate prolidase-dependence of prodrug cytotoxicity in the cell lines compared to that of the parent drug, melphalan.

MATERIALS AND METHODS

Hydrolysis, cell uptake, and cell proliferation studies of melphalan and the L: - and D: -proline prodrugs of melphalan, prophalan-L: and prophalan-D: , respectively, were conducted in the cancer cell lines using established procedures.

RESULTS

The bioactivation of prophalan-L: in the cancer cell lines exhibited high correlation with their prolidase expression levels (r (2) = 0.86). There were no significant differences in uptake of melphalan and its prodrugs. The cytotoxicity of prophalan-L: (GI(50)) in cancer cells also showed high correlation with prolidase expression (r (2) = 0.88), while prophalan-D: was ineffective at comparable concentrations. A prolidase targeting index (ratio of melphalan to prophalan-L: cytotoxicity normalized to their uptake) was computed and showed high correlation with prolidase expression (r (2) = 0.82).

CONCLUSIONS

The data corroborates the specificity of prophalan-L: activation by prolidase as well as prolidase-targeted cytotoxicity of prophalan-L: in cancer cell lines. Hence, prophalan-L: , a stable prodrug of melphalan, exhibits potential for efficiently targeting melanoma with reduced systemic toxicity.

Dual activities of human prolidase

The cDNA encoding human liver prolidase derived from a healthy adult's liver was cloned into the expression vector pPIC9K of Pichia pastoris to construct the recombination expression vector pPIC9K-P. The pPIC9K-P was digested by restriction enzyme Pme I, and then transformed into P. pastoris GS115 by electroporation. Transformants (the insertion recombinant) were induced by methanol to express the recombination protein. The optimal induction conditions (medium pH, methanol concentration and induction time) of the insertion transformant with the highest enzymatic activity were estimated by orthogonal experimental design L9(3(4)). The SDS-PAGE of the recombinant human prolidase (rh-prolidase) in induction medium showed a molecular weight of 73 kDa. The activities of the rh-prolidase and organophosphoric acid anhydrolases (OPAA) were assayed by colorimetric methods. The recombinant enzyme catalyzed the hydrolysis of organophosphorous compound soman as well as the hydrolysis of dipeptide Gly-Pro. Under the optimal induction conditions, the maximal activities of prolidase and OPAA came to 44.1 and 54.8 nmol/min/mg protein respectively in the medium supernatant. The rh-prolidase purified from the supernatant by ion exchange gradient chromatography (DEAE-Sepharose Fast Flow) and gel filtration chromatography (Sephacryl S-200 High Resolution) showed a single band by SDS-PAGE analysis. The purified rh-prolidase could decompose soman via hydrolytic reaction in vitro.

Characterization of the dinuclear metal center ofPyrococcus furiosusprolidase by analysis of targeted mutants

Prolidases are dipeptidases specific for cleavage of Xaa-Pro dipeptides. Pyrococcus furiosus prolidase is a homodimer having one Co-bound dinuclear metal cluster per monomer with one tightly bound Co(II) site and the other loosely bound (Kd 0.24 mM). To identify which Co site is tight-binding and which is loose-binding, site-directed mutagenesis was used to modify amino acid residues that participate in binding the Co1 (E-313 and H-284), the Co2 site (D-209) or the bidentate ligand (E-327). Metal-content, enzyme activity and CD-spectra analyses of D209A-, H284L-, and E327L-prolidase mutants show that Co1 is the tight-binding and Co2 the loose-binding metal center.

Purification and characterization of recombinant human liver prolidase expressed in Saccharomyces cerevisiae

The recombinant human liver prolidase (rh-prolidase, EC 3.4.13.9) from the lysate supernatant of engineering yeast Saccharomyces cerevisiae was purified in two steps employing anion-exchange gradient chromatography (DEAE-Sepharose fast flow) and gel filtration chromatography (Sephacryl S-200 high resolution). The purified recombinant protein furnished a single band with a molecular weight of 56 kD. Intensity scanning of the SDS-PAGE gel revealed that the prolidase accounted for more than 90% of total protein. The optimum pH of the catalytic reaction was 8.0. The enzyme was stimulated by Mn2+, but strongly inhibited by Cu2+ and Zn2+. The rh-prolidase expressed in S. cerevisiae had both dipeptidase and organophosphorus acid anhydrolase activity. It catalyzed the hydrolysis of soman and the dipeptide Gly -Pro. In a detoxification test in vitro, purified rh-prolidase was remarkably efficient at eliminating the toxicity of a lethal dose of soman, with the result that mice survived injection of such a dose.

Prolidase, a Potential Enzyme Target for Melanoma: Design of Proline-Containing Dipeptide-like Prodrugs

Bioinformatics tools such as Perl, Visual Basic, Cluster, and TreeView were used to analyze public gene expression databases in order to identify potential enzyme targets for prodrug strategies. The analyses indicated that prolidase might be a desirable enzyme target based on its differential expression in melanoma cancer cell lines and its high substrate specificity for dipeptides containing proline at the carboxy terminus. RT-PCR expression of prolidase and hydrolytic activity against N-glycyl-l-proline (GLY-PRO), a standard substrate of prolidase, determined in tumor cell lines, exhibited a high correlation (r(2) = 0.95). These results suggest the possibility of targeting prolidase with prodrugs of anticancer agents for enhanced selectivity. The feasibility of such a scenario was tested by (a) synthesizing prodrugs of melphalan that comprised linkage of the carboxy terminus of the l-phenylalanine moiety of melphalan to the N-terminus of l and d stereoisomers of proline and (b) determining their bioconversion and antiproliferative activities in SK-MEL-5 cells, a melanoma cancer cell line with high expression levels of prolidase. The results of hydrolysis studies of the l- and d-proline prodrugs of melphalan, designated as prophalan-l and prophalan-d, respectively, indicated a approximately 7-fold higher rate of activation of prophalan-l compared to prophalan-d in SK-MEL-5 cell homogenates. Prophalan-l exhibited cytotoxicity (GI(50) = 74.8 microM) comparable to that of melphalan (GI(50) = 57.0 microM) in SK-MEL-5 cells while prophalan-d was ineffective, suggesting that prolidase-specific activation to the parent drug may be essential for cytotoxic action. Thus, melphalan prodrugs such as prophalan-l that are cleavable by prolidase offer the potential for enhanced selectivity by facilitating cytotoxic activity only in cells overexpressing prolidase.

Functional and molecular characterization of rat intestinal prolidase

Genetic deficiency of prolidase can lead to severe problems in child development, including mental retardation. However, the exact pathogenesis of the disease is unclear. To understand the enzyme's physiologic functions, we studied the regulation of rat intestinal prolidase. The results indicated that 1) the activities of intestinal prolidase and its kinetic parameters (Km and Vmax) are site-dependent; 2) the jejunal prolidase activity was the most sensitive to the dietary restriction, and the duodenal and jejunal but not colonic kinetic parameters changed with dietary restriction; 3) the pH activity profile of jejunal prolidase at 24 h postfeeding was different from that at 48 h postfeeding, whereas the inhibition profiles of prolidase were qualitatively independent of dietary restriction; and 4) old-aged rats have lower prolidase activities in the small intestine. We also purified rat intestinal prolidase I to homogeneity. The characterization study indicated that the purified rat intestinal prolidase I is fairly similar to prolidase I from other species with a molecular weight of 116,000, which consisted of two monomers, 58,000 D each. The purified prolidase I has a Km value of 178 microM and a Vmax value of 601 micromol x min-1. mg protein-1. Screening of a rat intestinal cDNA library produced a 1.8-kb fragment that encodes the rat intestinal prolidase. This enzyme has 494 deduced amino acid sequence, which is 96% or 86% identical to mouse or human erythrocyte prolidase I. This represents the first report of a successful attempt to purify and clone an intestinal prolidase and of investigation to study prolidase regulation by diet.

Proline specific peptidases

Proline is unique among the 20 amino acids due to its cyclic structure. This specific conformation imposes many restrictions on the structural aspects of peptides and proteins and confers particular biological properties upon a wide range of physiologically important biomolecules. In order to adequately deal with such peptides, nature has developed a group of enzymes that recognise this residue specifically. These peptidases cover practically all situations where a proline residue might occur in a potential substrate. In this paper we endeavour to discuss these enzymes, particularly those responsible for peptide or protein hydrolysis at proline sites. We have detailed their discovery, biochemical attributes and substrate specificities and have provided information as to the methodology used to detect and manipulate their activities. We have also described the roles, or potential roles that these enzymes may play physiologically and the consequences of their dysfunction in varied disease states.

Direct monitoring of prolidase activity in cultured skin fibroblasts using capillary electrophoresis

Capillary electrophoresis (CE) was used as an alternative to current analysis schemes for detecting prolidase activity in erythrocytes and skin fibroblast cultures because of its unique selectivity and high resolving power. Kinetic measurement of peptide bond hydrolysis was performed using porcine kidney prolidase on different substrates (Gly-Pro, Leu-Pro and Ala-Pro) and by following the disappearance of the peptide-substrate's peak. The K(m) values obtained were in agreement with those previously reported. Interestingly, in the case of Phe-Pro as the substrate, simultaneous analysis of the product and parent peptide was possible, thus showing the superiority of the capillary electrophoresis (CE) assay with respect to the standard spectrophotometric method. The application of the CE technique to the characterization of prolidase activity in control and prolidase-deficient skin cultured fibroblasts was successful. Enzyme activity was easily calculated in all controls tested and the K(m) values determined were slightly lower than those obtained with the colorimetric reaction, thus confirming our assumption that the CE assay shows higher specificity than the ninhydrin technique. Our results demonstrate the feasibility of using CE as a simple and reliable technique for determining prolidase activity.

Hydrolysis of picolinylprolines by prolidase. A general mechanism for the dual-metal ion containing aminopeptidases

The velocity of enzymic cleavage of 4-substituted picolinylprolines by swine kidney prolidase approaches that of physiological dipeptides, but depends substantially upon the nature of the pyridine-ring substituent. The pH dependence of kcat/Km for picolinylproline is sigmoidal, with optimum activity on the acidic limb and a delimiting enzymic pKa of 6.6, unlike glycylproline (bell-shaped pH profile, maximum at pH 7.7). Productive chelation to an active site metal ion by the N terminus of substrates is indicated, with a water molecule ligated to that hyper(Lewis)acidic center prior to substrate binding supplying the pKa of 6.6. The rate-governing catalytic step differs according to the 4-substituent on the picolinyl residue; productive binding is slow in the case of electron-withdrawing groups, but subsequent nucleophilic addition to the metal ion-activated scissile linkage becomes controlling with more basic pyridine rings. Rate constants yield a Brønsted-type correlation with substrate pKa, providing a gauge of active-site Lewis acidity. A mechanism is suggested involving the cooperative participation of two especially acidic metal ions positioned adjacently within the active site (situated as in an homologous and structurally characterized aminopeptidase), with both serving to stabilize a bridging carboxamide-hydrate intermediate.