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

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.

Binding of dipeptidyl peptidase III to the oxidative stress cell sensor Kelch-like ECH-associated protein 1 is a two-step process

This work is about synergy of theory and experiment in revealing mechanism of binding of dipeptidyl peptidase III (DPP III) and Kelch-like ECH-associated protein 1 (KEAP1), the main cellular sensor of oxidative stress. The NRF2 ̶ KEAP1 signaling pathway is important for cell protection, but it is also impaired in many cancer cells where NRF2 target gene expression leads to resistance to chemotherapeutic drugs. DPP III competitively binds to KEAP1 in the conditions of oxidative stress and induces release of NRF2 and its translocation into nucleus. The binding is established mainly through the ETGE motif of DPP III and the Kelch domain of KEAP1. However, although part of a flexible loop, ETGE itself is firmly attached to the DPP III surface by strong hydrogen bonds. Using combined computational and experimental study, we found that DPP III ̶ Kelch binding is a two-step process comprising the endergonic loop detachment and exergonic DPP III ̶ Kelch interaction. Substitution of arginines, which keep the ETGE motif attached, decreases the work needed for its release and increases DPP III ̶ Kelch binding affinity. Interestingly, mutations of one of these arginine residues have been reported in cBioPortal for cancer genomics, implicating its possible involvement in cancer development. Communicated by Ramaswamy H. Sarma.

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.

The first dipeptidyl peptidase III from a thermophile: Structural basis for thermal stability and reduced activity

Dipeptidyl peptidase III (DPP III) isolated from the thermophilic bacteria Caldithrix abyssi (Ca) is a two-domain zinc exopeptidase, a member of the M49 family. Like other DPPs III, it cleaves dipeptides from the N-terminus of its substrates but differently from human, yeast and Bacteroides thetaiotaomicron (mesophile) orthologs, it has the pentapeptide zinc binding motif (HEISH) in the active site instead of the hexapeptide (HEXXGH). The aim of our study was to investigate structure, dynamics and activity of CaDPP III, as well as to find possible differences with already characterized DPPs III from mesophiles, especially B. thetaiotaomicron. The enzyme structure was determined by X-ray diffraction, while stability and flexibility were investigated using MD simulations. Using molecular modeling approach we determined the way of ligands binding into the enzyme active site and identified the possible reasons for the decreased substrate specificity compared to other DPPs III. The obtained results gave us possible explanation for higher stability, as well as higher temperature optimum of CaDPP III. The structural features explaining its altered substrate specificity are also given. The possible structural and catalytic significance of the HEISH motive, unique to CaDPP III, was studied computationally, comparing the results of long MD simulations of the wild type enzyme with those obtained for the HEISGH mutant. This study presents the first structural and biochemical characterization of DPP III from a thermophile.

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).