Human dipeptidyl peptidase III: insights into ligand binding from a combined experimental and computational approach

Let’s Talk about Sex Hormone Receptors and Their Physical Interaction with Sonic Hedgehog Protein: A Computational Study with Emphasis on Progesterone Receptor

The mature form of the sonic hedgehog protein (SHH-N) is the main canonical activator of the Hedgehog-GLI signaling pathway whose aberrant activity can lead to the development of hormone-dependent cancers like breast or prostate cancer. In this study, we employed computational methods to explore the potential binding of SHH-N with the progesterone receptor (PR), the sole member of the nuclear sex hormone receptor (SHRs) subfamily not previously linked to SHH-N. Through a combination of molecular docking, robust molecular dynamics (MD) simulations, and free energy calculations, we predicted a stable binding between SHH-N-cholesterol and PR. To validate our findings, we extended our in silico investigation to encompass the complexes between SHH-N-cholesterol and estrogen receptor alpha (ERα) and androgen receptor (AR)—complexes that have been experimentally confirmed in our prior studies. The calculations not only confirmed the stable binding of SHH-N-cholesterol with both ERα and AR but also revealed the strongest binding occurred with ERα, followed by AR and PR, suggesting a non-canonical interaction with potential biological significance. Microsecond-long MD simulations unveiled tight cholesterol binding in the SHRs’ binding sites, and we gained insights into sub-molecular interactions contributing to protein-protein stabilization in complexes involving PR and ERα for the first time. The MM/PBSA calculations indicated comparable binding affinities of PR for progesterone and SHH-N-cholesterol, with ERα exhibiting a more favorable enthalpy of binding with SHH-N-cholesterol than with estradiol.

Influence of Mutations of Conserved Arginines on Neuropeptide Binding in the DPP III Active Site

Dipeptidyl peptidase III (DPP III), a zinc exopeptidase, is involved in the final steps of intercellular protein degradation and has a marked affinity for opioid peptides such as enkephalins and endomorphins. Recently, we characterized a number of neuropeptides as potential substrates and inhibitors of human DPP III and provided an explanation for their differential behavior. These studies prompted us to investigate the influence of the conserved R399 and R669 on neuropeptides binding to DPP III. Measuring kinetic parameters in inhibitory assays, we found that mutation of R669 to Ala or Met significantly reduced the inhibitory properties of the slow substrates tynorphin and valorphin, whereas the effects on binding of the good substrates Arg₂-2NA and Leu-enkephalin were small. Molecular dynamics simulations of wild-type (WT) and mutant DPP III complexes with Leu-enkephalin, tynorphin, valorphin, and Arg₂-2NA in conjunction with calculations of binding free energies revealed that the lower inhibitory potency of slow substrates in the R669A mutant can be explained by the lower binding affinity of tynorphin and the higher propensity of valorphin to hydrolyze in the mutant than in WT. The R399A mutation was shown to affect the binding and/or hydrolysis of both good and slow substrates, with the effects on Leu-enkephalin being the most pronounced.

Structural and Functional Characterization of a New Bacterial Dipeptidyl Peptidase III Involved in Fruiting Body Formation in Myxobacteria

Dipeptidyl peptidase III (DPP III) is a zinc-dependent enzyme that specifically hydrolyzes dipeptides from the N-terminal of different-length peptides, and it is involved in a number of physiological processes. Here, DPP III with an atypical pentapeptide zinc binding motif (HELMH) was identified from Corallococcus sp. EGB. It was shown that the activity of recombined CoDPP III was optimal at 50 °C and pH 7.0 with high thermostability up to 60 °C. Unique to CoDPP III, the crystal structure of the ligand-free enzyme was determined as a dimeric and closed form. The relatively small inter-domain cleft creates a narrower entrance to the substrate binding site and the unfavorable binding of the bulky naphthalene ring. The ectopic expression of CoDPP III in M. xanthus DK1622 resulted in a 12 h head start in fruiting body development compared with the wild type. Additionally, the A-signal prepared from the starving DK1622-CoDPP III rescued the developmental defect of the asgA mutant, and the fruiting bodies were more numerous and closely packed. Our data suggested that CoDPP III played a role in the fruiting body development of myxobacteria through the accumulation of peptides and amino acids to act as the A-signal.

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.

Unravelling the inhibitory zinc ion binding site and the metal exchange mechanism in human DPP III

Dipeptidyl peptidase III (DPP III), a zinc-dependent exopeptidase, is widely distributed in organisms and present in almost all human tissues. In addition to its involvement in protein catabolism, it plays a role in oxidative stress and blood pressure regulation, and there is evidence of its involvement in pain modulation. Excess zinc ions have been found to inhibit its hydrolytic activity, but the binding affinity, binding site geometry, and mechanism of inhibitory activity have been unknown. Using several different computational approaches, we determined the inhibitory zinc ion binding site, its coordination and relative binding affinity. During some simulations the translocation of the zinc ion from the inhibitory to the catalytic binding site was observed, accompanied by movement of the catalytic zinc ion toward the exit of the substrate binding site. The traced behavior suggests an associative type of metal ion exchange, in which the formation of the ternary complex between enzyme and two metal ions precedes the exit of the catalytic metal ion. Differently from our previous findings that binding of a peptide induces partial opening of hDPP III, the globularity of the protein did not change in MD simulations of the hermorphin-like peptide bound to hDPP III with two zinc ions. However, the entrance to the interdomain cleft widens during Zn diffusion into the protein and was found to be the highest energy barrier in the process of metal translocation from the solvent to the active site. Finally, we discuss why excess zinc reduces enzyme activity.

SHH-N non-canonically sustains androgen receptor activity in androgen-independent prostate cancer cells

Prostate cancer is the second most frequent cancer diagnosed in men worldwide. Localized disease can be successfully treated, but advanced cases are more problematic. After initial effectiveness of androgen deprivation therapy, resistance quickly occurs. Therefore, we aimed to investigate the role of Hedgehog-GLI (HH-GLI) signaling in sustaining androgen-independent growth of prostate cancer cells. We found various modes of HH-GLI signaling activation in prostate cancer cells depending on androgen availability. When androgen was not deprived, we found evidence of non-canonical SMO signaling through the SRC kinase. After short-term androgen deprivation canonical HH-GLI signaling was activated, but we found little evidence of canonical HH-GLI signaling activity in androgen-independent prostate cancer cells. We show that in androgen-independent cells the pathway ligand, SHH-N, non-canonically binds to the androgen receptor through its cholesterol modification. Inhibition of this interaction leads to androgen receptor signaling downregulation. This implies that SHH-N activates the androgen receptor and sustains androgen-independence. Targeting this interaction might prove to be a valuable strategy for advanced prostate cancer treatment. Also, other non-canonical aspects of this signaling pathway should be investigated in more detail and considered when developing potential therapies.

New Zinc Ion Parameters Suitable for Classical MD Simulations of Zinc Metallopeptidases

The main aim of this work was to find parameters for the zinc ion in human dipeptidyl peptidase III (DPP III) active site that would enable its reliable modeling. Since the parameters publicly available failed to reproduce the zinc ion coordination in the enzyme, we developed a new set of the hybrid bonded/nonbonded parameters for the zinc ion suitable for molecular modeling of the human DPP III, dynamics, and ligand binding. The parameters allowed exchange of the water molecules coordinating the zinc ion and proved to be robust enough to enable reliable modeling not only of human DPP III and its orthologues but also of the other zinc-dependent peptidases with the zinc ion coordination similar to that in dipeptidyl peptidases III, i.e., peptidases with the zinc ion coordinated with two histidines and one glutamate. The new parameters were tested on a set of 21 different systems comprising 8 different peptidases, 5 DPP III orthologues, thermolysin, neprilysin, and aminopeptidase N, and the results are summarized in the second part of the article.

Oxidase or peptidase? A computational insight into a putative aflatoxin oxidase from Armillariella tabescens

Aflatoxin oxidase (AFO), an enzyme isolated from Armillariella tabescens, has been reported to degrade aflatoxin B1 (AFB1). However, recent studies reported sequence and structure similarities with the dipeptidyl peptidase III (DPP III) family of enzymes and confirmed peptidase activity toward DPP III substrates. In light of these investigations, an extensive computational study was performed in order to improve understanding of the AFO functions. Steered MD simulations revealed long-range domain motions described as protein opening, characteristic for DPPs III and necessary for substrate binding. Newly identified open and partially open forms of the enzyme closely resemble those of the human DPP III orthologue. Docking of a synthetic DPP III substrate Arg₂ -2-naphthylamide revealed a binding mode similar to the one found in crystal structures of human DPP III complexes with peptides with the S1 and S2 subsites' amino acid residues conserved. On the other hand, no energetically favorable AFB1 binding mode was detected, suggesting that aflatoxins are not good substrates of AFO. High plasticity of the zinc ion coordination sphere within the active site, consistent with that of up to date studied DPPs III, was observed as well. A detailed electrostatic analysis of the active site revealed a predominance of negatively charged regions, unsuitable for the binding of the neutral AFB1. The present study is in line with the most recent experimental study on this enzyme, both suggesting that AFO is a typical member of the DPP III family.

Concerted nitrogen inversion and hydrogen bonding to Glu451 are responsible for protein-controlled suppression of the reverse reaction in human DPP III

Human dipeptidyl-peptidase III (h.DPP III) is a zinc-exopeptidase that hydrolyses dipeptides from the N-terminus of its substrates. Its mechanism of action was assumed to be similar to that of thermolysin, but was never thoroughly investigated. This study presents the first insight into the reaction mechanism of h.DPP III, determined on the model and real (hydrated enzyme with Leu-enkephalin bound in the active site) systems. The Glu451-assisted water addition on amide carbon atoms and nitrogen inversion (i.e. change of pyramidalization on the leaving nitrogen) are shown to be the rate-determining steps with the activation energies in a good agreement with the experimental results for the Leu-enkephalin hydrolysis. The energy barrier for nucleophilic attack is about 28 kJ mol^-1, while barriers for the N-inversion differ as a consequence of the number of hydrogen bonds that have to be changed, which is smaller in the model active site than in the solvated enzyme. Although precisely defined geometry of the enzyme binding site puts an additional restraint on the hydrogen bonding interactions, at the same time it stimulates the forward reaction towards the final hydrolytic product. Namely, different from the model, the N-inversion is in a concerted fashion followed by favourable hydrogen bonding with Glu451 that immediately "locks" the system into the configuration where reversion to the enzyme-substrate complex is hardly achievable. Therefore we propose that the functional significance of DPP III is dual: to lower the energy barrier of the peptide hydrolysis and to suppress the reverse reaction.

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.

Conservation of the conformational dynamics and ligand binding within M49 enzyme family

The hydrogen deuterium exchange (HDX) mass spectrometry combined with molecular dynamics (MD) simulations was employed to investigate conformational dynamics and ligand binding within the M49 family (dipeptidyl peptidase III family). Six dipeptidyl peptidase III (DPP III) orthologues, human, yeast, three bacterial and one plant (moss) were studied. According to the results, all orthologues seem to be quite compact wherein DPP III from the thermophile Caldithrix abyssi seems to be the most compact. The protected regions are located within the two domains core and the overall flexibility profile consistent with semi-closed conformation as the dominant protein form in solution. Besides conservation of conformational dynamics within the M49 family, we also investigated the ligand, pentapeptide tynorphin, binding. By comparing HDX data obtained for unliganded protein with those obtained for its complex with tynorphin it was found that the ligand binding mode is conserved within the family. Tynorphin binds within inter-domain cleft, close to the lower domain β-core and induces its stabilization in all orthologues. Docking combined with MD simulations revealed details of the protein flexibility as well as of the enzyme–ligand interactions.

The hydrogen deuterium exchange (HDX) mass spectrometry combined with molecular dynamics (MD) simulations was employed to investigate conformational dynamics and ligand binding within the M49 family (dipeptidyl peptidase III family).

A novel Porphyromonas gingivalis enzyme: An atypical dipeptidyl peptidase III with an ARM repeat domain

Porphyromonas gingivalis, an asaccharolytic Gram-negative oral anaerobe, is a major pathogen associated with adult periodontitis, a chronic infective disease that a significant percentage of the human population suffers from. It preferentially utilizes dipeptides as its carbon source, suggesting the importance of dipeptidyl peptidase (DPP) types of enzyme for its growth. Until now DPP IV, DPP5, 7 and 11 have been extensively investigated. Here, we report the characterization of DPP III using molecular biology, biochemical, biophysical and computational chemistry methods. In addition to the expected evolutionarily conserved regions of all DPP III family members, PgDPP III possesses a C-terminal extension containing an Armadillo (ARM) type fold similar to the AlkD family of bacterial DNA glycosylases, implicating it in alkylation repair functions. However, complementation assays in a DNA repair-deficient Escherichia coli strain indicated the absence of alkylation repair function for PgDPP III. Biochemical analyses of recombinant PgDPP III revealed activity similar to that of DPP III from Bacteroides thetaiotaomicron, and in the range between activities of human and yeast counterparts. However, the catalytic efficiency of the separately expressed DPP III domain is ~1000-fold weaker. The structure and dynamics of the ligand-free enzyme and its complex with two different diarginyl arylamide substrates was investigated using small angle X-ray scattering, homology modeling, MD simulations and hydrogen/deuterium exchange (HDX). The correlation between the experimental HDX and MD data improved with simulation time, suggesting that the DPP III domain adopts a semi-closed or closed form in solution, similar to that reported for human DPP III. The obtained results reveal an atypical DPP III with increased structural complexity: its superhelical C-terminal domain contributes to peptidase activity and influences DPP III interdomain dynamics. Overall, this research reveals multifunctionality of PgDPP III and opens direction for future research of DPP III family proteins.

New findings about human dipeptidyl peptidase III based on mutations found in cancer

In this work we investigated the role of two highly conserved residues in the peptidase family M49, whose mutations G313W and R510W were detected in human cancer, using combined experimental and computational approaches.

Dynamic properties of dipeptidyl peptidase III from Bacteroides thetaiotaomicron and the structural basis for its substrate specificity – a computational study

Dynamics and enzyme activity of dipeptidyl peptidase III, wild type and mutants, from the human gut symbiont Bacteroides thetaiotaomicron.

Molecular simulations reveal that the long range fluctuations of human DPP III change upon ligand binding

The experimentally determined structures of human dipeptidyl peptidase III (DPP III) for the wild-type protein and for the complex of its E451A mutant with the peptide substrate, tynorphin, differ significantly in their overall shape. The two domains of the enzyme are separated by a wide cleft in the structure of the ligand-free enzyme, while in the ligand-bound mutant they are very close to each other, and the protein structure is extremely compact. Here, we applied a range of molecular dynamics simulation techniques to investigate the DPP III conformational landscape and the influence of ligand binding on the protein structure and dynamics. We used conventional, accelerated and steered methods to simulate DPP III and its complexes with tynorphin and with the preferred, synthetic, substrate Arg-Arg-2-naphthylamide. We found that DPP III can adopt a number of different forms in solution. The compact forms are more stable, but the open and partially closed states, spanning a wide range of conformations, can more effectively recognize the substrate which preferentially binds to the five-stranded β-core of the lower DPP III domain. The simulations indicated the existence of a dynamic equilibrium between open and semi-closed states and revealed two ways that the protein can close, leading to two distinct compact structures. The way in which the protein closes depends on the presence of the ligand.

Novel dipeptidyl hydroxamic acids that inhibit human and bacterial dipeptidyl peptidase III

Human dipeptidyl peptidase III (hDPP III), a zinc-metallopeptidase of the family M49, is an activator of the Keap1-Nrf2 cytoprotective pathway involved in defense against oxidative stress. Pathophysiological roles of DPP III have not been elucidated yet, partly due to the lack of specific inhibitors. We showed that substrate analog H-Tyr-Phe-NHOH is a strong competitive inhibitor of hDPP III, while H-Tyr-Gly-NHOH expresses much weaker inhibition. To investigate the effects of amino acid substitutions in inhibitor P1 position, we synthesized three new dipeptidyl hydroxamates and examined their influence on the activity of hDPP III and DPP III from the human gut symbiont Bacteroides thetaiotaomicron. The extent of inhibition of hDPP III, but not of bacterial enzyme, was dependent on the amino acid in P1. H-Phe-Phe-NHOH is recognized as one of the strongest inhibitors of hDPP III (K_i = 0.028 μM), and H-Phe-Leu-NHOH discriminated between human and bacterial ortholog of the M49 family.

Guanidiniocarbonyl-pyrrole-aryl conjugates as inhibitors of human dipeptidyl peptidase III: combined experimental and computational study

Good overlap of the standard DPP III substrate Arg-Arg-2NA (magenta) and the most efficient novel inhibitor (guanidiniocarbonyl-pyrrole-pyrene conjugate, blue-red) in the DPP III binding site.

Hunting the human DPP III active conformation: combined thermodynamic and QM/MM calculations

Multiple choices of the protein active conformations in flexible metalloenzymes complicate study of their catalytic mechanism. We used three different conformations of human dipeptidyl-peptidase III (DPP III) to investigate the influence of the protein environment on ligand binding and the Zn(2+) coordination. MD simulations followed by calculations of binding free energy components accomplished for a series of DPP III substrates, both synthetic and natural, revealed that binding of the β-strand shaped substrate to the five-stranded β-core of the compact DPP III form (in antiparallel fashion) is the preferred binding mode, in agreement with the experimentally determined structure of the DPP III inactive mutant-tynorphin complex (Bezerra et al., Proc. Natl. Acad. Sci. U. S. A., 2012, 109, 6525). Previously it was proposed that the catalytic mechanism of DPP III is similar to that of thermolysin, which assumes exchange of five and four coordinated Zn(2+), and activation of Zn-bound water by a nearby Glu. Our QM/MM calculations, performed for a total of 18 protein structures with different zinc ion environments, revealed that the 5-coordinated metal ion is more favourable than the 6-coordinated one in only the most compact DPP III form. Besides, in this structure E451 is H-bonded to the metal ion coordinating water. Also, our study revealed two constraints for the broad substrate specificity of DPP III. One is the possibility of the substrate adopting the β-strand shape and the other is its charged N-terminus. Altogether, we assume that the human DPP III active conformation would be the most compact form, similar to the "closed X-ray" DPP III structure.

The large scale conformational change of the human DPP III-substrate prefers the "closed" form

Human dipeptidyl peptidase III (DPP III) is a two domain metallo-peptidase from the M49 family. The wide interdomain cleft and broad substrate specificity suggest that this enzyme could experience significant conformational change. Long (>100 ns) molecular dynamics (MD) simulations of DPP III revealed large range conformational changes of the protein, suggesting the pre-existing equilibrium model for a substrate binding. The binding free energy calculations revealed tighter binding of the preferred synthetic substrate Arg-Arg-2-naphtylamide to the "closed" than to the "open" DPP III conformation. Our assumption that Asp372 plays a crucial role in the large scale interdomain closure was proved by the MD simulations of the Asp372Ala variant. During the same simulation time, the variant remained more "open" than the wild type protein. Apparently, Ala was not as efficient as Asp in establishing the interdomain interactions. According to the MM-PBSA calculations, the electrostatic component of the free energy of solvation turned out to be higher for the "closed" protein than for its less compact form. However, the gain in entropy due to water released from the interdomain cleft nicely balanced this negative effect.