Dipeptidyl peptidase III from rat liver cytosol: purification, molecular cloning and immunohistochemical localization

Neuropeptides, substrates and inhibitors of human dipeptidyl peptidase III, experimental and computational study - A new substrate identified

Dipeptidyl peptidase III (DPP III) is a cytosolic, two-domain zinc-exopeptidase. It is widely distributed in mammalian tissues, where it's involved in the final steps of normal intracellular protein degradation. However, its pronounced affinity for some bioactive peptides (angiotensins, enkephalins, and endomorphins) suggests more specific functions such as blood pressure regulation and involvement in pain regulation. We have investigated several different neuropeptides as potential substrates and inhibitors of human DPP III. The binding affinities and kinetic data determined by isothermal titration calorimetry, in combination with measurements of enzyme inhibition identified the hemorphin-related valorphin, tynorphin, S-tynorphin, and I-tynorphin as the most potent inhibitors of DPP III (actually slow substrates), whereas hemorphin-4 proved to be the best substrate of all neuropeptides examined. In addition, we have shown that the neuropeptides valorphin, Leu-valorphin-Arg, and the opioid peptide β-casomorphin, are DPP III substrates. The molecular modelling of selected peptides shows uniform binding to the lower domain β-strand residues of DPP III via peptide backbone atoms, but also previously unrecognized stabilizing interactions with conserved residues of the metal-binding site and catalytic machinery in the upper domain. The computational data helped explain the differences between substrates that are hydrolyzed effectively and those hydrolysed slowly by DPP III.

Dipeptidylamino-tripeptidylcarboxypeptidase NEMP3 and DPP3 (DPP III) are the same protein

Earlier it was shown that a group of extracellular low-specific metallopeptidases is present in the mammalian brain Kropotova and Mosevitsky (2016) [1]. These enzymes are weakly connected to the axonal ends of neurons. They were named Neuron bound Extracellular MetalloPeptidases (NEMP). The enzyme named NEMP3 turned out to be a unique exopeptidase that exhibits two activities: it removes the dipeptide from the N-end of the peptide, and it can also remove the tripeptide from the C-end of the peptide. Therefore, NEMP3 possesses the activities of dipeptidylaminopeptidase and of tripeptidylcarboxypeptidase. Mass spectrometry has revealed a homology of NEMP3 with DPP3 (DPP III, EC3.4.14.4), known as cytosolic dipeptidylaminopeptidase. We isolated DPP3 from rat and bovine liver and brain by the procedures used for this purpose by other authors. The effect of DPP3 on test peptides is the same as that of NEMP3. In particular, all DPP3 samples delete the tripeptide (AKF) from the C-end of the test peptide blocked at the N-end. The data obtained show that NEMP3 and DPP3 are the same protein (enzyme). Thus, DPP3 has two exopeptidase activities: the previously known activity of dipeptidylaminopeptidase and the activity of tripeptidylcarboxypeptidase discovered in this study. Another discovery is the extracellular activity of DPP 3 in the mammalian brain near synapses, which controls neuropeptides. DPP3 is involved in various processes, but in many cases its role remains to be clarified. The results obtained in this study will be useful for solving these questions.

Survey of Dipeptidyl Peptidase III Inhibitors: From Small Molecules of Microbial or Synthetic Origin to Aprotinin

Dipeptidyl peptidase III (DPP III) was originally thought to be a housekeeping enzyme that contributes to intracellular peptide catabolism. More specific roles for this cytosolic metallopeptidase, in the renin-angiotensin system and oxidative stress regulation, were confirmed, or recognized, only recently. To prove indicated (patho)physiological functions of DPP III in cancer progression, cataract formation and endogenous pain modulation, or to reveal new ones, selective and potent inhibitors are needed. This review encompasses natural and synthetic compounds with experimentally proven inhibitory activity toward mammalian DPP III. Except for the polypeptide aprotinin, all others are small molecules and include flavonoids, coumarin and benzimidazole derivatives. Presented are current strategies for the discovery or development of DPP III inhibitors, and mechanisms of inhibitory actions. The most potent inhibitors yet reported (propioxatin A and B, Tyr-Phe- and Phe-Phe-NHOH, and JMV-390) are active in low nanomolar range and contain hydroxamic acid moiety. High inhibitory potential possesses oligopeptides from the hemorphin group, valorphin and tynorphin, which are poor substrates of DPP III. The crystal structure of human DPP III-tynorphin complex enabled the design of the transition-state peptidomimetics inhibitors, effective in low micromolar concentrations. A new direction in the field is the development of fluorescent inhibitor for monitoring DPP III activity.

The emerging role of dipeptidyl peptidase 3 in pathophysiology

Dipeptidyl peptidase 3 (DPP3), a zinc-dependent aminopeptidase, is a highly conserved enzyme among higher animals. The enzyme cleaves dipeptides from the N-terminus of tetra- to decapeptides, thereby taking part in activation as well as degradation of signalling peptides critical in physiological and pathological processes such as blood pressure regulation, nociception, inflammation and cancer. Besides its catalytic activity, DPP3 moonlights as a regulator of the cellular oxidative stress response pathway, e.g., the Keap1-Nrf2 mediated antioxidative response. The enzyme is also recognized as a key modulator of the renin-angiotensin system. Recently, DPP3 has been attracting growing attention within the scientific community, which has significantly augmented our knowledge of its physiological relevance. Herein, we review recent advances in our understanding of the structure and catalytic activity of DPP3, with a focus on attributing its molecular architecture and catalytic mechanism to its wide-ranging biological functions. We further highlight recent intriguing reports that implicate a broader role for DPP3 as a valuable biomarker in cardiovascular and renal pathologies and furthermore discuss its potential as a promising drug target.

Demystifying DPP III Catalyzed Peptide Hydrolysis—Computational Study of the Complete Catalytic Cycle of Human DPP III Catalyzed Tynorphin Hydrolysis

Dipeptidyl peptides III (DPP III) is a dual-domain zinc exopeptidase that hydrolyzes peptides of varying sequence and size. Despite attempts to elucidate and narrow down the broad substrate-specificity of DPP III, there is no explanation as to why some of them, such as tynorphin (VVYPW), the truncated form of the endogenous heptapeptide spinorphin, are the slow-reacting substrates of DPP III compared to others, such as Leu-enkephalin. Using quantum molecular mechanics calculations followed by various molecular dynamics techniques, we describe for the first time the entire catalytic cycle of human DPP III, providing theoretical insight into the inhibitory mechanism of tynorphin. The chemical step of peptide bond hydrolysis and the substrate binding to the active site of the enzyme and release of the product were described for DPP III in complex with tynorphin and Leu-enkephalin and their products. We found that tynorphin is cleaved by the same reaction mechanism determined for Leu-enkephalin. More importantly, we showed that the product stabilization and regeneration of the enzyme, but not the nucleophilic attack of the catalytic water molecule and inversion at the nitrogen atom of the cleavable peptide bond, correspond to the rate-determining steps of the overall catalytic cycle of the enzyme.

Purification, kinetic and functional characterization of membrane bound dipeptidyl peptidase-III from NCDC 252: a probiotic lactic acid bacteria

Pediococcus acidilactici is a probiotic lactic acid bacteria possessing studied in-vitro probiotic properties. Study of membrane proteins is crucial in developing technological and health applications of probiotic bacteria. Genome analysis of Pediococcus acidilactici revealed about more than 60 proteases/peptidases which need characterization. Dipeptidyl peptidase-III (DPP-III) is studied for first time in prokaryotes and it is a membrane protein in P. acidilactici that has been purified to apparent homogeneity. The enzyme was purified 81.66 fold with 36.75% yield. The specific activity of purified DPP-III was 202.67 U/mg. The protein moved as single band on native PAGE. The purity was also confirmed by in-situ gel assay. However SDS-PAGE analysis revealed it as high molecular weight heterotetramer with molecular weight of 108 kDa. The enzyme was maximally active at pH 8.5 and at 37 C. Purified DPP-III specifically hydrolyzed Arg-Arg-4-βNA with micromolar affinity (K_m = 9.0 µM) and none of studied endopeptidase and monopeptidase substrate was hydrolyzed. Inhibition study revealed purified DPP-III to be a serine protease with involvement of metal ion at active site. The significance of this enzyme as membrane protein is yet to be studied.

Dipeptidyl peptidase 3, a novel protease from Leishmania braziliensis

The increase of leishmaniasis cases worldwide and the emergence of Leishmania strains resistant to current treatments make necessary to find new therapeutic targets. Proteases are appealing drug targets because they play pivotal roles in facilitating parasite survival and promoting pathogenesis. Enzymes belonging to the dipeptidyl peptidase 3 (DPP3) group have been described in different organisms such as mammals, insects and yeast, in which these enzymes have been involved in both protein turnover and protection against oxidative damage. The aim of this work was to characterize the structure and function of the Leishmania braziliensis DPP3 (LbDPP3) protein as the first step to elucidate its suitability as a potential drug target. Sequence alignment showed 43% of identity between LbDPP3 and its human orthologous (hDPP3) enzyme. Although the modeled protein adopted a globally conserved three-dimensional (3D) structure, structural differences were found in the vicinity of the active site and the substrate binding-cleft. In addition, the Leishmania protein was expressed as a soluble recombinant protein and its kinetics parameters were determined using the z-Arginine-Arginine-AMC substrate. The LbDPP3 activity was maximal at pH values between 8.0–8.5. Interestingly, classical enzyme inhibitors such as the tynorphin and its derivative peptide IVYPW were found to actively inhibit the LbDPP3 activity. Moreover, these DPP3 inhibitors showed a detrimental effect upon parasite survival, decreasing the viability of promastigotes by up to 29%. Finally, it was observed that LbDPP3 was equally expressed along the in vitro differentiation from promastigotes to axenic amastigotes. In conclusion, these findings suggest that the L. brazileinsis DPP3 could be a promising drug target.

The vasoprotective axes of the renin-angiotensin system: Physiological relevance and therapeutic implications in cardiovascular, hypertensive and kidney diseases

The renin-angiotensin system (RAS) is undisputedly one of the most prominent endocrine (tissue-to-tissue), paracrine (cell-to-cell) and intracrine (intracellular/nuclear) vasoactive systems in the physiological regulation of neural, cardiovascular, blood pressure, and kidney function. The importance of the RAS in the development and pathogenesis of cardiovascular, hypertensive and kidney diseases has now been firmly established in clinical trials and practice using renin inhibitors, angiotensin-converting enzyme (ACE) inhibitors, type 1 (AT₁) angiotensin II (ANG II) receptor blockers (ARBs), or aldosterone receptor antagonists as major therapeutic drugs. The major mechanisms of actions for these RAS inhibitors or receptor blockers are mediated primarily by blocking the detrimental effects of the classic angiotensinogen/renin/ACE/ANG II/AT₁/aldosterone axis. However, the RAS has expanded from this classic axis to include several other complex biochemical and physiological axes, which are derived from the metabolism of this classic axis. Currently, at least five axes of the RAS have been described, with each having its key substrate, enzyme, effector peptide, receptor, and/or downstream signaling pathways. These include the classic angiotensinogen/renin/ACE/ANG II/AT₁ receptor, the ANG II/APA/ANG III/AT₂/NO/cGMP, the ANG I/ANG II/ACE2/ANG (1-7)/Mas receptor, the prorenin/renin/prorenin receptor (PRR or Atp6ap2)/MAP kinases ERK1/2/V-ATPase, and the ANG III/APN/ANG IV/IRAP/AT₄ receptor axes. Since the roles and therapeutic implications of the classic angiotensinogen/renin/ACE/ANG II/AT₁ receptor axis have been extensively reviewed, this article will focus primarily on reviewing the roles and therapeutic implications of the vasoprotective axes of the RAS in cardiovascular, hypertensive and kidney diseases.

Novel Therapeutic Role for Dipeptidyl Peptidase III in the Treatment of Hypertension

Dipeptidyl peptidase III (DPP III) cleaves dipeptide residues from the N terminus of polypeptides ranging from 3 to 10 amino acids in length and is implicated in pathophysiological processes through the breakdown of certain oligopeptides or their fragments. In this study, we newly identified the biochemical properties of DPP III for angiotensin II (Ang II), which consists of 8 amino acids. DPP III quickly and effectively digested Ang II with Km = 3.7×10(-6) mol/L. In the in vivo experiments, DPP III remarkably reduced blood pressure in Ang II-infused hypertensive mice without alteration of heart rate. DPP III did not affect hemodynamics in noradrenalin-induced hypertensive mice or normotensive mice, suggesting specificity for Ang II. When DPP III was intravenously injected every other day for 4 weeks after Ang II osmotic minipump implantation in mice, Ang II-induced cardiac fibrosis and hypertrophy were significantly attenuated. This DPP III effect was at least similar to that caused by an angiotensin receptor blocker candesartan. Furthermore, administration of DPP III dramatically reduced the increase in urine albumin excretion and kidney injury and inflammation markers caused by Ang II infusion. Both DPP III and candesartan administration showed slight additive inhibition in the albumin excretion. These results reveal a novel potential use of DPP III in the treatment of hypertension and its protective effects on hypertension-sensitive organs, such as the heart and kidneys.

Peptidase inhibitors in the MEROPS database

The MEROPS website (http://merops.sanger.ac.uk) includes information on peptidase inhibitors as well as on peptidases and their substrates. Displays have been put in place to link peptidases and inhibitors together. The classification of protein peptidase inhibitors is continually being revised, and currently inhibitors are grouped into 67 families based on comparisons of protein sequences. These families can be further grouped into 38 clans based on comparisons of tertiary structure. Small molecule inhibitors are important reagents for peptidase characterization and, with the increasing importance of peptidases as drug targets, they are also important to the pharmaceutical industry. Small molecule inhibitors are now included in MEROPS and over 160 summaries have been written.

The first structure of dipeptidyl-peptidase III provides insight into the catalytic mechanism and mode of substrate binding

Dipeptidyl-peptidases III (DPP III) are zinc-dependent enzymes that specifically cleave the first two amino acids from the N terminus of different length peptides. In mammals, DPP III is associated with important physiological functions and is a potential biomarker for certain types of cancer. Here, we present the 1.95-A crystal structure of yeast DPP III representing the prototype for the M49 family of metallopeptidases. It shows a novel fold with two domains forming a wide cleft containing the catalytic metal ion. DPP III exhibits no overall similarity to other metallopeptidases, such as thermolysin and neprilysin, but zinc coordination and catalytically important residues are structurally conserved. Substrate recognition is accomplished by a binding site for the N terminus of the peptide at an appropriate distance from the metal center and by a series of conserved arginine residues anchoring the C termini of different length substrates.

Human dipeptidyl peptidase III acts as a post-proline-cleaving enzyme on endomorphins

Dipeptidyl peptidase III (DPP III) is a zinc exopeptidase with an implied role in the mammalian pain-modulatory system owing to its high affinity for enkephalins and localisation in the superficial laminae of the spinal cord dorsal horn. Our study revealed that this human enzyme hydrolyses opioid peptides belonging to three new groups, endomorphins, hemorphins and exorphins. The enzymatic hydrolysis products of endomorphin-1 were separated and quantified by capillary electrophoresis and the kinetic parameters were determined for human DPP III and rat DPP IV. Both peptidases cleave endomorphin-1 at comparable rates, with liberation of the N-terminal Tyr-Pro. This is the first evidence of DPP III acting as an endomorphin-cleaving enzyme.

Identification and characterization of two dipeptidyl-peptidase III isoforms in Drosophila melanogaster

Dipeptidyl-peptidase III (DPP III) hydrolyses small peptides with a broad substrate specificity. It is thought to be involved in a major degradation pathway of the insect neuropeptide proctolin. We report the purification and characterization of a soluble DPP III from 40 g Drosophila melanogaster. Western blot analysis with anti-(DPP III) serum revealed the purification of two proteins of molecular mass 89 and 82 kDa. MS/MS analysis of these proteins resulted in the sequencing of 45 and 41 peptide fragments, respectively, confirming approximately 60% of both annotated D. melanogaster DPP III isoforms (CG7415-PC and CG7415-PB) predicted at 89 and 82 kDa. Sequencing also revealed the specific catalytic domain HELLGH in both isoforms, indicating that they are both effective in degrading small peptides. In addition, with a probe specific for D. melanogaster DPP III, northern blot analysis of fruit fly total RNA showed two transcripts at approximately 2.6 and 2.3 kb, consistent with the translation of 89-kDa and 82-kDa DPP III proteins. Moreover, the purified enzyme hydrolyzed the insect neuropeptide proctolin (Km approximately 4 microm) at the second N-terminal peptide bound, and was inhibited by the specific DPP III inhibitor tynorphin. Finally, anti-(DPP III) immunoreactivity was observed in the central nervous system of D. melanogaster larva, supporting a functional role for DPP III in proctolin degradation. This study shows that DPP III is in actuality synthesized in D. melanogaster as 89-kDa and 82-kDa isoforms, representing two native proteins translated from two alternative mRNA transcripts.

Highly reactive cysteine residues are part of the substrate binding site of mammalian dipeptidyl peptidases III

Dipeptidyl peptidase III (DPP III) is a cytosolic zinc-exopeptidase involved in the intracellular protein catabolism of eukaryotes. Although inhibition by thiol reagents is a general feature of DPP III originating from various species, the function of activity important sulfhydryl groups is still inadequately understood. The present study of the reactivity of these groups was undertaken in order to clarify their biological significance. The inactivation kinetics of human and rat DPP III by sulfhydryl reagent p-hydroxy-mercuribenzoate (pHMB) was monitored by determination of the enzyme's residual activity with fluorimetric detection. Inactivation of this human enzyme exhibited pseudo-first-order kinetics, suggesting that all reactive SH-groups have equivalent reactivity, and the second-order rate constant was calculated to be 3523+/-567M(-1)min(-1). Rat DPP III was hyperreactive to pHMB and showed biphasic kinetics indicating two classes of reactive SH-groups. The second-order rate constants of 3540M(-1)s(-1) for slower reacting sulfhydryl, and 21,855M(-1)s(-1) for faster reacting sulfhydryl were obtained from slopes of linear plots of pseudo-first-order constants versus reagent concentration. Peptide substrates protected both mammalian DPPs III from inactivation by pHMB. Physiological concentrations of biological thiols and H(2)O(2) inactivated the rat DPP III. Human enzyme was resistant to H(2)O(2) attack and less affected by reduced glutathione (GSH) than the rat homologue. A significantly lower DPP III level, determined by activity measurement and Western blotting, was found in the cytosols of highly oxygenated rat tissues. These results provide kinetic evidence that cysteine residues are involved in substrate binding of mammalian DPPs III.

Tumor cytosol dipeptidyl peptidase III activity is increased with histological aggressiveness of ovarian primary carcinomas

OBJECTIVE

Proteolytic enzymes have been implicated in the progression of various human malignancies, including ovarian cancer. The enhanced expression of dipeptidyl peptidase III (DPP III) was found in endometrial carcinomas of various histological types and grade. The aim of this study was to assess activity of DPP III in ovarian tissue specimens and to correlate it with clinico-pathological data.

METHODS

DPP III hydrolytic activity toward Arg-Arg-2-naphthylamide was determined in 108 ovarian tissue cytosol specimens of 79 patients. The data obtained for 41 ovarian primary carcinoma specimens were stratified according to clinical stage, histological grade and type, and age of the patients.

RESULTS

Median DPP III activity expressed as milliunits per milligram protein was 6 in normal ovarian tissues (n = 29), 6.5 in benign ovarian tumors (n = 19), 19.5 in primary ovarian carcinomas (n = 41), 12.5 in nonepithelial primary ovarian tumors (n = 7), and 22.1 in metastatic ovarian malignancies (n = 12). A significant rise in median DPP III specific activity was observed in malignant ovarian tumors (of epithelial, nonepithelial, and metastatic origin), but not in benign ovarian tumors, compared to the activity in normal tissue. A significant difference of DPP III expression was found between the group of normal tissues and tumors of clinical stage I and II, of grade 2 and 3, of serous and mucinous histologic type.

CONCLUSIONS

DPP III activity of benign ovarian tumors equaled that in normal ovarian tissue. In malignant neoplasms of the ovary it increased with growing histologic grade.

Characterization of a functionally expressed dipeptidyl aminopeptidase III from Drosophila melanogaster

A Drosophila melanogaster cDNA clone (GH01916) encoding a putative 723-residue long (82 kDa) protein (CG 7415) and displaying 50% identity with mammalian cytosolic dipeptidyl aminopeptidase (DPP) III was functionally expressed in Schneider S2 cells. Immunocytochemical studies using anti-(rat liver DPP III) Ig indicated the expression of this putative DPP III at the outer cell membrane and into the cytosol of transfected cells. Two protein bands (82 and 86 kDa) were immunologically detected after PAGE and Western blot of cytosol or membrane prepared from transfected cells. Western blot analysis of partially purified D. melanogaster DPP III confirmed the overexpression of these two protein bands into the cytosol and on the membranes of transfected cells. Despite the identification of six potential glycosylation sites, PAGE showed that these protein bands were not shifted after deglycosylation experiments. The partially purified enzyme hydrolysed the insect myotropic neuropeptide proctolin (Arg-Tyr-Leu-Pro-Thr) at the Tyr-Leu bond (Km approximately 4 micro m). In addition, low concentration of the specific DPP III inhibitor tynorphin prevented proctolin degradation (IC50 = 0.62 +/- 0.15 micro m). These results constitute the first characterization of an evolutionarily conserved insect DPP III that is expressed as a cytosolic and a membrane peptidase involved in proctolin degradation.

Inhibition of recombinant dipeptidyl peptidase III by synthetic hemorphin-like peptides

In order to find the most effective antagonist for dipeptidyl peptidase III degrading enkephalin, we synthesized hemorphin-like pentapeptides with aliphatic or aromatic amino acids at the N-termini, such as VVYPW, LVYPW, IVYPW, YVYPW, FVYPW and WVYPW. Among those pentapeptides, IVYPW and WVYPW showed the strongest inhibitory activity toward rDPP III. The K(i) values of IVYPW and WVYPW were 0.100+/-0.011 and 0.126+/-0.015 microM (mean+/-S.E.), respectively. The order of K(i) values was Ile> or =Trp>Phe> or =Tyr>Leu>Ala>Val>Ser>Gly. rDPP III activity is inhibited in a non-competitive manner by these peptides. The peptide VYPW did not inhibit rDPP III activity, but the sequence is essential for the expression of inhibitory activity.

Peptidases play an important role in cataractogenesis: an immunohistochemical study on lenses derived from Shumiya cataract rats

The role of proteolytic enzymes in Shumiya cataract rats in alterations to lens proteins during cataract formation was studied immunohistochemically using antibodies against exopeptidases, such as lysosomal dipeptidyl peptidase II (DPP II), cytosolic dipeptidyl peptidase III, and soluble and membrane-bound alanyl aminopeptidases, and against cytosolic endopeptidases such as mu- and m-calpains, and 20S proteasome. AlphaB-crystallin was detected as a proteolytic marker in the lenses. A constant immunoreactivity against all the antibodies employed was observed in the lens epithelium independent of the strain and age of the rats. A weak immunoreactivity against exo- and endopeptidases and an intense reactivity against alphaB-crystallin were observed in the lens fibres of control rats at all ages. The immunoreactivity of these peptidases in lens fibres increased with age in cataract rats, but that of alphaB-crystallin decreased. No reactivity against exo- and endopeptidases was seen in the perinuclear region of lenses of control rats at all ages or in Shumiya cataract rats at 8 and 10 weeks of age, but an intense reactivity against these peptidases was observed in the lens perinuclear region of lenses in cataract rats at 12 and 14 weeks of age. AlphaB-crystallin immunoreactivity was observed with ordered striations in the lens perinuclear region of all control rats whereas the striations in this area of cataract rat lens were disorganized. Membrane-bound alanyl aminopeptidase was detected feebly in the lens epithelium and fibres of both types of rat at all weeks of age. These findings indicate that exo- and endopeptidases, except for membrane-bound alanyl aminopeptidase, are expressed intensively and are age-dependent. Conversely, the amount of alphaB-crystallin decreased with age in lens fibres of cataract rats. Calpains (mu- and m-), 20S proteasome, dipeptidyl peptidases II and III and soluble alanyl aminopeptidase are thought to induce lens opacification kinetically during cataract formation in Shumiya cataract rats through the intracellular turnover of lens proteins.

Purification, partial sequencing and characterization of an insect membrane dipeptidyl aminopeptidase that degrades the insect neuropeptide proctolin

Two proctolin-binding proteins solubilized from 1600 cockroach hindgut membranes were purified 1000-fold using five chromatography steps. Twenty-five micrograms of protein were recovered from the final size-exclusion chromatography as a single peak eluting at 74 kDa, whereas two major bands at 80 and 76 kDa were identified after silver staining of electrophoresis gels. The fragments, sequenced by tandem mass spectrometry and the Edman method, revealed a high homology with rat liver dipeptidyl aminopeptidase (DPP) III and a significant homology between the cockroach-purified proteins. From analysis of the Drosophila genome sequence database, it was possible to identify a putative DPP sharing high homology with the sequences obtained from the cockroach purified proteins and with the rat DPP III. Anti-(rat liver DPP III) Ig reacted specifically with both cockroach-purified proteins in Western blot analysis. The purified proteins removed the N-terminal dipeptide from the insect myotropic neuropeptide proctolin (Arg-Tyr-Leu-Pro-Thr) with a Km value of 3.8 +/- 1.1 microM. The specific DPP III inhibitor tynorphin prevented the degradation of proctolin by the purified insect DPP (IC50 = 0.68 microM). These results provide strong evidence that the cockroach-purified proteins represent an insect membrane DPP, presumably present in Drosophila, and that it is closely related to vertebrate DPP III.

Human and rat dipeptidyl peptidase III: biochemical and mass spectrometric arguments for similarities and differences

Dipeptidyl peptidase (DPP III) was purified from rat and human erythrocytes using an identical procedure. Electrophoretic analyses revealed the same molecular size and pI for both enzymes. The molecular mass of the human enzyme, measured by matrix-assisted laser desorption/ionization MS, was 82500+/-60 Da. Its tryptic peptide mass profile was determined using the same technique, and the amino acid sequence of two internal peptides was obtained by tandem MS and Edman degradation. A search of databases revealed a high similarity between the human erythrocyte and rat liver DPP III: 21 matches out of 34 detected peptides were found, covering 40% of the total sequence. Matched peptides included the peptide harboring the characteristic HELLGH sequence motif, and a stretch of 19 identical amino acids, containing Glu, a putative ligand of active site zinc. Both enzymes preferred Arg-Arg-2-naphthylamide, and were activated by micromolar Co2+, differing in their pH optima and kcat/Km. Zn2+ ions, sulfhydryl reagents, and aminopeptidase inhibitors, especially probestin, inhibited the rat DPP III more potently. The two enzymes showed the highest affinity for angiotensin III (Ki < 1 microM) and a preference for ahydrophobic residue at the P1' site. However, significant differences in the binding constants for several peptides indicated non-identity in the active site topography of human and rat erythrocyte DPP III.

Alteration of rat dipeptidyl peptidase III by site-directed mutagenesis: cysteine(176) is a regulatory residue for the enzyme activity

To comprehend the importance of cysteine residues for the regulation of enzyme activity, we replaced each of seven cysteine residues in rat dipeptidyl peptidase III cDNA with alanine, glycine, or glutamic acid residue using site-directed mutagenesis. Each mutated cDNA was expressed in E. coli (BL21), and each expressed DPP III was purified to apparent homogeneity on SDS-polyacrylamide gel electrophoresis. Six of the mutant proteins had similar activity to that of the wild-type enzyme, whereas the activity of the Cys(176) --> Ala mutant enzyme was only 25-35% of that of the wild-type enzyme activity. This mutant enzyme was resistant against both PCMB and NEM. Furthermore, both Cys(176) --> Gly and Cys(176) --> Glu mutated enzymes showed no DPP III activity. These seven mutated enzymes contained significant amounts of zinc, as determined by atomic absorption spectrometry. The results indicate that Cys(176) is essential for the regulation of DPP III activity.