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

Diversity and structural-functional insights of alpha-solenoid proteins

Alpha-solenoids are a significant and diverse subset of structured tandem repeat proteins (STRPs) that are important in various domains of life. This review examines their structural and functional diversity and highlights their role in critical cellular processes such as signaling, apoptosis, and transcriptional regulation. Alpha-solenoids can be classified into three geometric folds: low curvature, high curvature, and corkscrew, as well as eight subfolds: ankyrin repeats; Huntingtin, elongation factor 3, protein phosphatase 2A, and target of rapamycin; armadillo repeats; tetratricopeptide repeats; pentatricopeptide repeats; Pumilio repeats; transcription activator-like; and Sel-1 and Sel-1-like repeats. These subfolds represent distinct protein families with unique structural properties and functions, highlighting the versatility of alpha-solenoids. The review also discusses their association with disease, highlighting their potential as therapeutic targets and their role in protein design. Advances in state-of-the-art structure prediction methods provide new opportunities and challenges in the functional characterization and classification of this kind of fold, emphasizing the need for continued development of methods for their identification and proper data curation and deposition in the main databases.

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.

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.

Computational Modeling of Molecular Structures Guided by Hydrogen-Exchange Data

Data produced by hydrogen-exchange monitoring experiments have been used in structural studies of molecules for several decades. Despite uncertainties about the structural determinants of hydrogen exchange itself, such data have successfully helped guide the structural modeling of challenging molecular systems, such as membrane proteins or large macromolecular complexes. As hydrogen-exchange monitoring provides information on the dynamics of molecules in solution, it can complement other experimental techniques in so-called integrative modeling approaches. However, hydrogen-exchange data have often only been used to qualitatively assess molecular structures produced by computational modeling tools. In this paper, we look beyond qualitative approaches and survey the various paradigms under which hydrogen-exchange data have been used to quantitatively guide the computational modeling of molecular structures. Although numerous prediction models have been proposed to link molecular structure and hydrogen exchange, none of them has been widely accepted by the structural biology community. Here, we present as many hydrogen-exchange prediction models as we could find in the literature, with the aim of providing the first exhaustive list of its kind. From purely structure-based models to so-called fractional-population models or knowledge-based models, the field is quite vast. We aspire for this paper to become a resource for practitioners to gain a broader perspective on the field and guide research toward the definition of better prediction models. This will eventually improve synergies between hydrogen-exchange monitoring and molecular modeling.

Dipeptidyl-peptidases: Key enzymes producing entry forms of extracellular proteins in asaccharolytic periodontopathic bacterium Porphyromonas gingivalis

Porphyromonas gingivalis, a pathogen of chronic periodontitis, is an asaccharolytic microorganism that solely utilizes nutritional amino acids as its energy source and cellular constituents. The bacterium is considered to incorporate proteinaceous nutrients mainly as dipeptides, thus exopeptidases that produce dipeptides from polypeptides are critical for survival and proliferation. We present here an overview of dipeptide production by P. gingivalis mediated by dipeptidyl-peptidases (DPPs), e.g., DPP4, DPP5, DPP7, and DPP11, serine exopeptidases localized in periplasm, which release dipeptides from the N-terminus of polypeptides. Additionally, two other exopeptidases, acylpeptidyl-oligopeptidase (AOP) and prolyl tripeptidyl-peptidase A (PTP-A), which liberate N-terminal acylated di-/tri-peptides and tripeptides with Pro at the third position, respectively, provide polypeptides in an acceptable form for DPPs. Hence, a large fraction of dipeptides is produced from nutritional polypeptides by DPPs with differential specificities in combination with AOP and PTP-A. The resultant dipeptides are then incorporated across the inner membrane mainly via a proton-dependent oligopeptide transporter (POT), a member of the major facilitator superfamily. Recent studies also indicate that DPP4 and DPP7 directly link between periodontal and systemic diseases, such as type 2 diabetes mellitus and coagulation abnormality, respectively. Therefore, these dipeptide-producing and incorporation molecules are considered to be potent targets for prevention and treatment of periodontal and related systemic diseases.

Metabolic cooperativity between Porphyromonas gingivalis and Treponema denticola

Background

 Porphyromonas gingivalis and Treponema denticola are proteolytic periodontopathogens that co-localize in polymicrobial subgingival plaque biofilms, display in vitro growth symbiosis and synergistic virulence in animal models of disease. These symbioses are underpinned by a range of metabolic interactions including cooperative hydrolysis of glycine-containing peptides to produce free glycine, which T. denticola uses as a major energy and carbon source.

Objective

 To characterize the P. gingivalis gene products essential for these interactions. Methods: The P. gingivalis transcriptome exposed to cell-free T. denticola conditioned medium was determined using RNA-seq. P. gingivalis proteases potentially involved in hydrolysis of glycine-containing peptides were identified using a bioinformatics approach.

Results

 One hundred and thirty-twogenes displayed differential expression, with the pattern of gene expression consistent with succinate cross-feeding from T. denticola to P. gingivalis and metabolic shifts in the P. gingivalis folate-mediated one carbon superpathway. Interestingly, no P. gingivalis proteases were significantly up-regulated. Three P. gingivalis proteases were identified as candidates and inactivated to determine their role in the release of free glycine. P. gingivalis PG0753 and PG1788 but not PG1605 are involved in the hydrolysis of glycine-containing peptides, making free glycine available for T. denticola utilization.

Conclusion

 Collectively these metabolic interactions help to partition resources and engage synergistic interactions between these two species.

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.

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).