N-linked glycosylation of dipeptidyl peptidase IV (CD26): effects on enzyme activity, homodimer formation, and adenosine deaminase binding

Directly monitoring the dynamic in vivo metabolisms of hyperpolarized 13C-oligopeptides

Peptides play essential roles in biological phenomena, and, thus, there is a growing interest in detecting in vivo dynamics of peptide metabolisms. Dissolution-dynamic nuclear polarization (d-DNP) is a state-of-the-art technology that can markedly enhance the sensitivity of nuclear magnetic resonance (NMR), providing metabolic and physiological information in vivo. However, the hyperpolarized state exponentially decays back to the thermal equilibrium, depending on the spin-lattice relaxation time (T1). Because of the limitation in T1, peptide-based DNP NMR molecular probes applicable in vivo have been limited to amino acids or dipeptides. Here, we report the direct detection of in vivo metabolic conversions of hyperpolarized 13C-oligopeptides. Structure-based T1 relaxation analysis suggests that the C-terminal [1-13C]Gly-d2 residue affords sufficient T1 for biological uses, even in relatively large oligopeptides, and allowed us to develop 13C-β-casomorphin-5 and 13C-glutathione. It was found that the metabolic response and perfusion of the hyperpolarized 13C-glutathione in the mouse kidney were significantly altered in a model of cisplatin-induced acute kidney injury.

Cosolvent Molecular Dynamics Applied to DPP4, DPP8 and DPP9: Reproduction of Important Binding Features and Use in Inhibitor Design

We present our efforts in computational drug design against dipeptidyl peptidase 4 (DPP4), DPP8 and DPP9. We applied cosolvent molecular dynamics (MD) simulations to these three protein targets of interest. Our primary motivation is the growing interest in DPP8 and DPP9 as emerging drug targets. Due to the high similarity between DPP4, DPP8 and DPP9, DPP4 was also included in these analyses. The cosolvent molecular dynamics simulations reproduce key ligand binding features and known binding pockets, while also highlighting interesting fragment positions for future ligand optimization. The resulting fragment maps from the cosolvent molecular dynamics are freely available for use in future research (https://github.com/UAMC-Olivier/DPP489_cosolvent_MD/). Detailed instructions for easy visualization of the fragment maps are provided, ensuring that the results are usable by both computational and medicinal chemists. Additionally, we used the fragment maps to search for the binding pockets with significant potential using an algorithmic approach combining top fragment locations. To discover novel binding scaffolds, a limited pharmacophore screening was performed, where the pharmacophores were based on the analyses of the cosolvent simulations. Unfortunately, inhibitory potencies were in the higher micromolar range, but we optimized the resulting scaffolds in silico using relative binding free energy calculations for future inhibitor design and synthesis.

Defining the Cell Surface Cysteinome Using Two-Step Enrichment Proteomics

The plasma membrane proteome is a rich resource of functionally important and therapeutically relevant protein targets. Distinguished by high hydrophobicity, heavy glycosylation, disulfide-rich sequences, and low overall abundance, the cell surface proteome remains undersampled in established proteomic pipelines, including our own cysteine chemoproteomics platforms. Here, we paired cell surface glycoprotein capture with cysteine chemoproteomics to establish a two-stage enrichment method that enables chemoproteomic profiling of cell Surface Cysteinome. Our "Cys-Surf" platform captures >2,800 total membrane protein cysteines in 1,046 proteins, including 1,907 residues not previously captured by bulk proteomic analysis. By pairing Cys-Surf with an isotopic chemoproteomic readout, we uncovered 821 total ligandable cysteines, including known and novel sites. Cys-Surf also robustly delineates redox-sensitive cysteines, including cysteines prone to activation-dependent changes to cysteine oxidation state and residues sensitive to addition of exogenous reductants. Exemplifying the capacity of Cys-Surf to delineate functionally important cysteines, we identified a redox sensitive cysteine in the low-density lipoprotein receptor (LDLR) that impacts both the protein localization and uptake of low-density lipoprotein (LDL) particles. Taken together, the Cys-Surf platform, distinguished by its two-stage enrichment paradigm, represents a tailored approach to delineate the functional and therapeutic potential of the plasma membrane cysteinome.

Structural Similarities, in Relation with the Cross-Reactivity, of Hymenoptera Allergenic Dipeptidyl Peptidases IV-An Overall Comparison Including a New Dipeptidyl Peptidase IV Sequence from Vespa velutina

(1) Background: Dipeptidyl Peptidases IV (DPPIVs), present in many organisms, are minor components in the venoms of Hymenoptera, where they have been identified as cross-reactive allergenic molecules. Considering that the structure of homologous DPPIVs is well characterized, we aimed to explain which regions have higher similarity among these proteins and present a comparison among them, including a new Vespa velutina DPPIV sequence. Moreover, two cases of sensitization to DPPIVs in wasp- and honeybee-sensitized patients are presented. (2) Methods: Proteomic analyses have been performed on the venom of the Asian hornet Vespa velutina to demonstrate the sequence of its DPPIV (allergen named Vesp v 3, with sequence accession number P0DRB8, and with the proteomic data available via ProteomeXchange with the identifier PXD046030). A comparison performed through their alignments and analysis of the three-dimensional structure showed a region with higher similarity among Hymenoptera DPPIVs. Additionally, ImmunoCAP™ determinations (including specific inhibition experiments), as well as IgE immunoblotting, are performed to demonstrate the allergenicity of Api m 5 and Ves v 3. (3) Results and Conclusions: The data presented demonstrate that the similarities among Hymenoptera DPPIVs are most likely localized at the C-terminal region of these enzymes. In addition, a higher similarity of the Vespa/Vespula DPPIVs is shown. The clinical cases analyzed demonstrated the allergenicity of Api m 5 and Ves v 3 in the sera of the allergic patients, as well as the presence of this minor component in the preparations used in venom immunotherapy.

Defining the Cell Surface Cysteinome using Two-step Enrichment Proteomics

The plasma membrane proteome is a rich resource of functional and therapeutically relevant protein targets. Distinguished by high hydrophobicity, heavy glycosylation, disulfide-rich sequences, and low overall abundance, the cell surface proteome remains undersampled in established proteomic pipelines, including our own cysteine chemoproteomics platforms. Here we paired cell surface glycoprotein capture with cysteine chemoproteomics to establish a two-stage enrichment method that enables chemoproteomic profiling of cell Surface Cysteinome. Our "Cys-Surf" platform captures >2,800 total membrane protein cysteines in 1,046 proteins, including 1,907 residues not previously captured by bulk proteomic analysis. By pairing Cys-Surf with an isotopic chemoproteomic readout, we uncovered 821 total ligandable cysteines, including known and novel sites. Cys-Surf also robustly delineates redox-sensitive cysteines, including cysteines prone to activation-dependent changes to cysteine oxidation state and residues sensitive to addition of exogenous reductants. Exemplifying the capacity of Cys-Surf to delineate functionally important cysteines, we identified a redox sensitive cysteine in the low-density lipoprotein receptor (LDLR) that impacts both the protein localization and uptake of LDL particles. Taken together, the Cys-Surf platform, distinguished by its two-stage enrichment paradigm, represents a tailored approach to delineate the functional and therapeutic potential of the plasma membrane cysteinome.

Role of Dipeptidyl Peptidase-4 (DPP4) on COVID-19 Physiopathology

DPP4/CD26 is a single-pass transmembrane protein with multiple functions on glycemic control, cell migration and proliferation, and the immune system, among others. It has recently acquired an especial relevance due to the possibility to act as a receptor or co-receptor for SARS-CoV-2, as it has been already demonstrated for other coronaviruses. In this review, we analyze the evidence for the role of DPP4 on COVID-19 risk and clinical outcome, and its contribution to COVID-19 physiopathology. Due to the pathogenetic links between COVID-19 and diabetes mellitus and the hyperinflammatory response, with the hallmark cytokine storm developed very often during the disease, we dive deep into the functions of DPP4 on carbohydrate metabolism and immune system regulation. We show that the broad spectrum of functions regulated by DPP4 is performed both as a protease enzyme, as well as an interacting partner of other molecules on the cell surface. In addition, we provide an update of the DPP4 inhibitors approved by the EMA and/or the FDA, together with the newfangled approval of generic drugs (in 2021 and 2022). This review will also cover the effects of DPP4 inhibitors (i.e., gliptins) on the progression of SARS-CoV-2 infection, showing the role of DPP4 in this disturbing disease.

Genetic Insights into the Middle East Respiratory Syndrome Coronavirus Infection among Saudi People

BACKGROUND

The Middle East respiratory syndrome coronavirus (MERS-CoV) was isolated for the first time in Saudi Arabia from a patient suffering from atypical pneumonia. The Saudi Genome database was built by King Abdulaziz Medical City via the next-generation sequencing of 7000 candidates.

METHOD

A large list of point mutations were reported in the region of the dipeptidyl peptidase 4 (DPP4) gene. The DPP4 amino acid residues correlated to MERS-CoV entry and the site of activity of DPP4 inhibitors was investigated. We retrieved the SNPs (Single-Nucleotide Polymorphism) with a variation frequency of >0.05.

RESULTS

SNP 2:162,890,175 and SNP 2:162,891,848 in the intronic region were located within 50 bp of amino acid residues responsible for MERS-CoV entry, amino acids 259-296 and 205-258, respectively. The variation frequency of SNP 2:162,890,175 was 2321 out of 2379 screened individuals. Moreover, mutation of SNP 2:162,891,848, which is located near amino acid residues E205 and E206 (crucial for the activity of DPP4 inhibitors), occurred in 76 out of 2379 screened individuals.

CONCLUSIONS

Our study shows high variation frequency in the DPP4 region reported in the Saudi Genome database. The identified SNPs are of high significance for MERS-CoV infection in better understanding disease pathogenesis.

A Novel Purification Procedure for Active Recombinant Human DPP4 and the Inability of DPP4 to Bind SARS-CoV-2

Proteases catalyse irreversible posttranslational modifications that often alter a biological function of the substrate. The protease dipeptidyl peptidase 4 (DPP4) is a pharmacological target in type 2 diabetes therapy primarily because it inactivates glucagon-like protein-1. DPP4 also has roles in steatosis, insulin resistance, cancers and inflammatory and fibrotic diseases. In addition, DPP4 binds to the spike protein of the MERS virus, causing it to be the human cell surface receptor for that virus. DPP4 has been identified as a potential binding target of SARS-CoV-2 spike protein, so this question requires experimental investigation. Understanding protein structure and function requires reliable protocols for production and purification. We developed such strategies for baculovirus generated soluble recombinant human DPP4 (residues 29–766) produced in insect cells. Purification used differential ammonium sulphate precipitation, hydrophobic interaction chromatography, dye affinity chromatography in series with immobilised metal affinity chromatography, and ion-exchange chromatography. The binding affinities of DPP4 to the SARS-CoV-2 full-length spike protein and its receptor-binding domain (RBD) were measured using surface plasmon resonance and ELISA. This optimised DPP4 purification procedure yielded 1 to 1.8 mg of pure fully active soluble DPP4 protein per litre of insect cell culture with specific activity >30 U/mg, indicative of high purity. No specific binding between DPP4 and CoV-2 spike protein was detected by surface plasmon resonance or ELISA. In summary, a procedure for high purity high yield soluble human DPP4 was achieved and used to show that, unlike MERS, SARS-CoV-2 does not bind human DPP4.

N-glycosylation in Spodoptera frugiperda (Lepidoptera: Noctuidae) midgut membrane-bound glycoproteins

Spodoptera frugiperda is a widely distributed agricultural pest. It has previously been established that glycoproteins in the midgut microvillar membrane of insects are targets for toxins produced by different organisms as well as plant lectins. However, there is still little information about the N-glycome of membrane-bound midgut glycoproteins in Lepidoptera and other insect groups. The present study used mass spectrometry-based approaches to characterize the N-glycoproteins present in the midgut cell microvilli of Spodoptera frugiperda. We subjected midgut cell microvilli proteins to proteolytic digestion and enriched the resulting glycopeptides prior to analysis. We also performed endoglycosidase release of N-glycans in the presence of H₂¹⁸O determining the compositions of released N-glycans by MALDI-TOF MS analysis and established the occupancy of the potential N-glycosylation sites. We report here a total of 160 glycopeptides, representing 25 N-glycan compositions associated with 70 sites on 35 glycoproteins. Glycan compositions consistent with oligomannose, paucimannose and complex/hybrid N-glycans represent 35, 30 and 35% of the observed glycans, respectively. The two most common N-glycan compositions were the complex/hybrid Hex₃HexNAc₄dHex₄ and the paucimannose structure that contains only the doubly-fucosylated trimannosylchitobiose core Hex₃HexNAc₂dHex₂, each appearing in 22 occupied sites (13.8%). These findings enlighten aspects of the glycobiology of lepidopteran midgut microvilli.

Tackling dipeptidyl peptidase IV in neurological disorders

Dipeptidyl peptidase IV (DPP-IV) is a serine protease best known for its role in inactivating glucagon-like peptide-1 (GLP-1), pituitary adenylate cyclase-activating polypeptide (PACAP) and glucose-dependent insulinotropic peptide (GIP), three stimulators of pancreatic insulin secretion with beneficial effects on glucose disposal. Owing to the relationship between DPP-IV and these peptides, inhibition of DPP-IV enzyme activity is considered as an attractive treatment option for diabetic patients. Nonetheless, increasing studies support the idea that DPP-IV might also be involved in the development of neurological disorders with a neuroinflammatory component, potentially through its non-incretin activities on immune cells. In this review article, we aim at highlighting recent literature describing the therapeutic value of DPP-IV inhibitors for the treatment of such neurological conditions. Finally, we will illustrate some of the promising results obtained using berberine, a plant extract with potent inhibitory activity on DPP-IV.

Dipeptidyl Peptidase-4 and Adolescent Idiopathic Scoliosis: Expression in Osteoblasts

It has been proposed that girls with adolescent idiopathic scoliosis (AIS) tend to have a taller stature and a lower body mass index. Energy homeostasis, that is known to affect bone growth, could contribute to these characteristics. In circulation, dipeptidyl peptidase-4 (DPP-4) inactivates glucagon-like peptide-1 (GLP-1), an incretin that promotes insulin secretion and sensitivity. Our objectives were to investigate DPP-4 status in plasma and in osteoblasts of AIS subjects and controls and to evaluate the regulatory role of metabolic effectors on DPP-4 expression. DPP-4 activity was assessed in plasma of 113 girls and 62 age-matched controls. Osteoblasts were isolated from bone specimens of AIS patients and controls. Human cells were incubated with glucose, insulin, GLP-1 and butyrate. Gene and protein expressions were evaluated by RT-qPCR and Western blot. Our results showed 14% inferior plasma DPP-4 activity in AIS patients when compared to healthy controls (P = 0.0357). Similarly, osteoblasts derived from AIS subjects had lower DPP-4 gene and protein expression than controls by 90.5% and 57.1% respectively (P < 0.009). DPP-4 expression was regulated in a different manner in osteoblasts isolated from AIS participants compared to controls. Our results suggest a role for incretins in AIS development and severity.

Heterogeneity of molecular forms of dipeptidyl peptidase-IV and fibroblast activation protein in human glioblastomas

BACKGROUND AND AIMS

Proteolytic enzymes contribute to the progression of various cancers. We previously reported increased expression of the proline specific peptidases dipeptidyl peptidase-IV (DPP-IV) and its closest paralogue fibroblast activation protein (FAP) in human glioblastomas. Here we analyze the molecular heterogeneity of DPP-IV and FAP in glioblastomas.

METHODS

ELISA, isoelectric focusing, 1D and 2D electrophoresis followed by WB or enzyme overlay assay were utilized to analyze DPP-IV and FAP isoforms. Cell fractionation using a Percoll gradient and deglycosylation with PNGase F were performed to analyze the possible basis of DPP-IV and FAP microheterogeneity.

RESULTS

Molecular forms of DPP-IV with an estimated molecular weight of 140-160 kDa and a pI predominantly 5.8 were detected in human glioblastoma; in some tumors additional isoforms with a more acidic (3.5-5.5) as well as alkaline (8.1) pI were revealed. Using 2D electrophoresis, two to three molecular forms of FAP with an alkaline (7.0-8.5) pI and an estimated MW of 120-140 kDa were identified in glioblastoma tissues. In glioma cell lines in vitro, several isoforms of both enzymes were expressed, however the alkalic forms present in glioblastoma tissues were not detected. Removal of N-linked oligosaccharides decreased the estimated molecular weight of both enzymes; the overall pattern of molecular forms nevertheless remained unchanged.

CONCLUSION

Several isoforms of DPP-IV and FAP are present in glioblastoma tissue. The absence of alkaline isoforms of both enzymes in glioma cell lines however suggests that isoforms from other, most likely stromal, cell types contribute to the overall pattern seen in glioblastoma tissues.

Functional similarities between the dictyostelium protein AprA and the human protein dipeptidyl-peptidase IV

Autocrine proliferation repressor protein A (AprA) is a protein secreted by Dictyostelium discoideum cells. Although there is very little sequence similarity between AprA and any human protein, AprA has a predicted structural similarity to the human protein dipeptidyl peptidase IV (DPPIV). AprA is a chemorepellent for Dictyostelium cells, and DPPIV is a chemorepellent for neutrophils. This led us to investigate if AprA and DPPIV have additional functional similarities. We find that like AprA, DPPIV is a chemorepellent for, and inhibits the proliferation of, D. discoideum cells, and that AprA binds some DPPIV binding partners such as fibronectin. Conversely, rAprA has DPPIV-like protease activity. These results indicate a functional similarity between two eukaryotic chemorepellent proteins with very little sequence similarity, and emphasize the usefulness of using a predicted protein structure to search a protein structure database, in addition to searching for proteins with similar sequences.

Diabetes, hypertension, and chronic kidney disease progression: role of DPP4

The protein dipeptidyl peptidase 4 (DPP4) is a target in diabetes management and reduction of associated cardiovascular risk. Inhibition of the enzymatic function and genetic deletion of DPP4 is associated with tremendous benefits to the heart, vasculature, adipose tissue, and the kidney in rodent models of obesity, diabetes and hypertension, and associated complications. The recently concluded, "Saxagliptin Assessment of Vascular Outcomes Recorded in Patients with Diabetes Mellitus-Thrombolysis in Myocardial Infarction 53" trial revealed a reduction in proteinuria in chronic kidney disease patients (stages 1-3). These results have spurred immense interest in the nonenzymatic and enzymatic role of DPP4 in the kidney. DPP4 is expressed predominantly in the glomeruli and S1-S3 segments of the nephron and to a lesser extent in other segments. DPP4 is known to facilitate absorption of cleaved dipeptides and regulate the function of the sodium/hydrogen exchanger-3 in the proximal tubules. DPP4, also known as CD26, has an important role in costimulation of lymphocytes via caveolin-1 on antigen-presenting cells in peripheral blood. Herein, we present our perspectives for the ongoing interest in the role of DPP4 in the kidney.

Effects of Glycosylation on the Enzymatic Activity and Mechanisms of Proteases

Posttranslational modifications are an important feature of most proteases in higher organisms, such as the conversion of inactive zymogens into active proteases. To date, little information is available on the role of glycosylation and functional implications for secreted proteases. Besides a stabilizing effect and protection against proteolysis, several proteases show a significant influence of glycosylation on the catalytic activity. Glycans can alter the substrate recognition, the specificity and binding affinity, as well as the turnover rates. However, there is currently no known general pattern, since glycosylation can have both stimulating and inhibiting effects on activity. Thus, a comparative analysis of individual cases with sufficient enzyme kinetic and structural data is a first approach to describe mechanistic principles that govern the effects of glycosylation on the function of proteases. The understanding of glycan functions becomes highly significant in proteomic and glycomic studies, which demonstrated that cancer-associated proteases, such as kallikrein-related peptidase 3, exhibit strongly altered glycosylation patterns in pathological cases. Such findings can contribute to a variety of future biomedical applications.

Regulation of Chemokine Activity - A Focus on the Role of Dipeptidyl Peptidase IV/CD26

Chemokines are small, chemotactic proteins that play a crucial role in leukocyte migration and are, therefore, essential for proper functioning of the immune system. Chemokines exert their chemotactic effect by activation of chemokine receptors, which are G protein-coupled receptors (GPCRs), and interaction with glycosaminoglycans (GAGs). Furthermore, the exact chemokine function is modulated at the level of posttranslational modifications. Among the different types of posttranslational modifications that were found to occur in vitro and in vivo, i.e., proteolysis, citrullination, glycosylation, and nitration, NH₂-terminal proteolysis of chemokines has been described most intensively. Since the NH₂-terminal chemokine domain mediates receptor interaction, NH₂-terminal modification by limited proteolysis or amino acid side chain modification can drastically affect their biological activity. An enzyme that has been shown to provoke NH₂-terminal proteolysis of various chemokines is dipeptidyl peptidase IV or CD26. This multifunctional protein is a serine protease that preferably cleaves dipeptides from the NH₂-terminal region of peptides and proteins with a proline or alanine residue in the penultimate position. Various chemokines possess such a proline or alanine residue, and CD26-truncated forms of these chemokines have been identified in cell culture supernatant as well as in body fluids. The effects of CD26-mediated proteolysis in the context of chemokines turned out to be highly complex. Depending on the chemokine ligand, loss of these two NH₂-terminal amino acids can result in either an increased or a decreased biological activity, enhanced receptor specificity, inactivation of the chemokine ligand, or generation of receptor antagonists. Since chemokines direct leukocyte migration in homeostatic as well as pathophysiologic conditions, CD26-mediated proteolytic processing of these chemotactic proteins may have significant consequences for appropriate functioning of the immune system. After introducing the chemokine family together with the GPCRs and GAGs, as main interaction partners of chemokines, and discussing the different forms of posttranslational modifications, this review will focus on the intriguing relationship of chemokines with the serine protease CD26.

GlycoMinestruct: a new bioinformatics tool for highly accurate mapping of the human N-linked and O-linked glycoproteomes by incorporating structural features

Glycosylation plays an important role in cell-cell adhesion, ligand-binding and subcellular recognition. Current approaches for predicting protein glycosylation are primarily based on sequence-derived features, while little work has been done to systematically assess the importance of structural features to glycosylation prediction. Here, we propose a novel bioinformatics method called GlycoMine^struct(http://glycomine.erc.monash.edu/Lab/GlycoMine_Struct/) for improved prediction of human N- and O-linked glycosylation sites by combining sequence and structural features in an integrated computational framework with a two-step feature-selection strategy. Experiments indicated that GlycoMine^struct outperformed NGlycPred, the only predictor that incorporated both sequence and structure features, achieving AUC values of 0.941 and 0.922 for N- and O-linked glycosylation, respectively, on an independent test dataset. We applied GlycoMine^struct to screen the human structural proteome and obtained high-confidence predictions for N- and O-linked glycosylation sites. GlycoMine^struct can be used as a powerful tool to expedite the discovery of glycosylation events and substrates to facilitate hypothesis-driven experimental studies.

Rapid and sensitive detection of early esophageal squamous cell carcinoma with fluorescence probe targeting dipeptidylpeptidase IV

Early detection of esophageal squamous cell carcinoma (ESCC) is an important prognosticator, but is difficult to achieve by conventional endoscopy. Conventional lugol chromoendoscopy and equipment-based image-enhanced endoscopy, such as narrow-band imaging (NBI), have various practical limitations. Since fluorescence-based visualization is considered a promising approach, we aimed to develop an activatable fluorescence probe to visualize ESCCs. First, based on the fact that various aminopeptidase activities are elevated in cancer, we screened freshly resected specimens from patients with a series of aminopeptidase-activatable fluorescence probes. The results indicated that dipeptidylpeptidase IV (DPP-IV) is specifically activated in ESCCs, and would be a suitable molecular target for detection of esophageal cancer. Therefore, we designed, synthesized and characterized a series of DPP-IV-activatable fluorescence probes. When the selected probe was topically sprayed onto endoscopic submucosal dissection (ESD) or surgical specimens, tumors were visualized within 5 min, and when the probe was sprayed on biopsy samples, the sensitivity, specificity and accuracy reached 96.9%, 85.7% and 90.5%. We believe that DPP-IV-targeted activatable fluorescence probes are practically translatable as convenient tools for clinical application to enable rapid and accurate diagnosis of early esophageal cancer during endoscopic or surgical procedures.

The opioid effects of gluten exorphins: asymptomatic celiac disease

Gluten-containing cereals are a main food staple present in the daily human diet, including wheat, barley, and rye. Gluten intake is associated with the development of celiac disease (CD) and related disorders such as diabetes mellitus type I, depression, and schizophrenia. However, until now, there is no consent about the possible deleterious effects of gluten intake because of often failing symptoms even in persons with proven CD. Asymptomatic CD (ACD) is present in the majority of affected patients and is characterized by the absence of classical gluten-intolerance signs, such as diarrhea, bloating, and abdominal pain. Nevertheless, these individuals very often develop diseases that can be related with gluten intake. Gluten can be degraded into several morphine-like substances, named gluten exorphins. These compounds have proven opioid effects and could mask the deleterious effects of gluten protein on gastrointestinal lining and function. Here we describe a putative mechanism, explaining how gluten could "mask" its own toxicity by exorphins that are produced through gluten protein digestion.

The Role of Dipeptidyl Peptidase - 4 Inhibitors in Diabetic Kidney Disease

Despite major advances in the understanding of the molecular mechanisms that underpin the development of diabetic kidney disease, current best practice still leaves a significant proportion of patients with end-stage kidney disease requiring renal replacement therapy. This is on a background of an increasing diabetes epidemic worldwide. Although kidney failure is a major cause of morbidity the main cause of death remains cardiovascular in nature. Hence, diabetic therapies which are both “cardio-renal” protective seem the logical way forward. In this review, we discuss the dipeptidyl peptidase 4 (DPP4) inhibitors (DPP4inh), which are glucose-lowering agents used clinically and their role in diabetic kidney disease with specific focus on renoprotection and surrogate markers of cardiovascular disease. We highlight the novel pleiotropic effects of DPP4 that make it an attractive additional target to combat the fibrotic and inflammatory pathways in diabetic kidney disease and also discuss the current literature on the cardiovascular safety profile of DPP4inh. Clearly, these observed renoprotective effects will need to be confirmed by clinical trials to determine whether they translate into beneficial effects to patients with diabetes.

Glycosylation patterns of kidney proteins differ in rat diabetic nephropathy

Diabetic nephropathy often progresses to end-stage kidney disease and, ultimately, to renal replacement therapy. Hyperglycemia per se is expected to have a direct impact on the biosynthesis of N- and O-linked glycoproteins. This study aims to establish the link between protein glycosylation and progression of experimental diabetic kidney disease using orthogonal methods. Kidneys of streptozotocin-diabetic and control rats were harvested at three different time points post streptozotocin injection. A panel of 12 plant lectins was used in the screening of lectin blots. The lectins UEAI, PHA-E, GSI, PNA, and RCA identified remarkable disease-associated differences in glycoprotein expression. Lectin affinity chromatography followed by mass spectrometric analyses led to the identification of several glycoproteins involved in salt-handling, angiogenesis, and extracellular matrix degradation. Our data confirm a substantial link between glycosylation signature and diabetes progression. Furthermore, as suggested by our findings on dipeptidyl peptidase-IV, altered protein glycosylation may reflect changes in biochemical properties such as enzymatic activity. Thus, our study demonstrates the unexplored potential of protein glycosylation analysis in the discovery of molecules linked to diabetic kidney disease.

Pharmacology, physiology, and mechanisms of action of dipeptidyl peptidase-4 inhibitors

Dipeptidyl peptidase-4 (DPP4) is a widely expressed enzyme transducing actions through an anchored transmembrane molecule and a soluble circulating protein. Both membrane-associated and soluble DPP4 exert catalytic activity, cleaving proteins containing a position 2 alanine or proline. DPP4-mediated enzymatic cleavage alternatively inactivates peptides or generates new bioactive moieties that may exert competing or novel activities. The widespread use of selective DPP4 inhibitors for the treatment of type 2 diabetes has heightened interest in the molecular mechanisms through which DPP4 inhibitors exert their pleiotropic actions. Here we review the biology of DPP4 with a focus on: 1) identification of pharmacological vs physiological DPP4 substrates; and 2) elucidation of mechanisms of actions of DPP4 in studies employing genetic elimination or chemical reduction of DPP4 activity. We review data identifying the roles of key DPP4 substrates in transducing the glucoregulatory, anti-inflammatory, and cardiometabolic actions of DPP4 inhibitors in both preclinical and clinical studies. Finally, we highlight experimental pitfalls and technical challenges encountered in studies designed to understand the mechanisms of action and downstream targets activated by inhibition of DPP4.

Distribution, classification, domain architectures and evolution of prolyl oligopeptidases in prokaryotic lineages

Background

Prolyl oligopeptidases (POPs) are proteolytic enzymes, widely distributed in all the kingdoms of life. Bacterial POPs are pharmaceutically important enzymes, yet their functional and evolutionary details are not fully explored. Therefore, current analysis is aimed at understanding the distribution, domain architecture, probable biological functions and gene family expansion of POPs in bacterial and archaeal lineages.

Results

Exhaustive sequence analysis of 1,202 bacterial and 91 archaeal genomes revealed ~3,000 POP homologs, with only 638 annotated POPs. We observed wide distribution of POPs in all the analysed bacterial lineages. Phylogenetic analysis and co-clustering of POPs of different phyla suggested their common functions in all the prokaryotic species. Further, on the basis of unique sequence motifs we could classify bacterial POPs into eight subtypes. Analysis of coexisting domains in POPs highlighted their involvement in protein-protein interactions and cellular signaling. We proposed significant extension of this gene family by characterizing 39 new POPs and 158 new α/β hydrolase members.

Conclusions

Our study reflects diversity and functional importance of POPs in bacterial species. Many genomes with multiple POPs were identified with high sequence variations and different cellular localizations. Such anomalous distribution of POP genes in different bacterial genomes shows differential expansion of POP gene family primarily by multiple horizontal gene transfer events.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-985) contains supplementary material, which is available to authorized users.

Dipeptidyl peptidase IV inhibition activates CREB and improves islet vascularization through VEGF-A/VEGFR-2 signaling pathway

Substitution of pancreatic islets is a potential therapy to treat diabetes and it depends on reconstitution of islet’s capillary network. In this study, we addressed the question whether stabilization of Glucagon-Like-Peptide-1 (GLP-1) by inhibiting Dipeptidyl Peptidase-IV (DPP-IV) increases β-cell mass by modulating vascularization. Mouse or porcine donor islets were implanted under kidney capsule of diabetic mice treated with DPP-IV inhibitor sitagliptin. Grafts were analyzed for insulin production, β-cell proliferation and vascularization. In addition, the effect of sitagliptin on sprouting and Vascular Endothelial Growth Factor (VEGF)-A expression was examined ex vivo. The cAMP response element-binding (CREB) and VEGF-A/ Vascular Endothelial Growth Factor Receptor (VEGFR)-2 signaling pathway leading to islet vascularization was explored. Sitagliptin increased mean insulin content of islet grafts and area of insulin-positive tissue as well as β-cell proliferation. Interestingly, sitagliptin treatment also markedly increased endothelial cell proliferation, microvessel density and blood flow. Finally, GLP-1 (7-36) stimulated sprouting and VEGF expression, which was significantly enhanced by sitagliptin- mediated inhibition of DPP-IV. Our in vivo data demonstrate that sitagliptin treatment phosphorylated CREB and induced islet vascularization through VEGF-A/VEGFR-2 signaling pathway. This study paves a new pathway for improvement of islet transplantation in treating diabetes mellitus.

Enhanced activity of Rhizomucor miehei lipase by deglycosylation of its propeptide in Pichia pastoris

Many studies have demonstrated that the properties of enzymes expressed in eukaryotes can be affected by the position and extent of glycosylation on enzyme. In this study, two potential glycosylation sites (the 8th and the 58th asparagine) were identified and the effect of propeptide glycosylation on Rhizomucor miehei lipase (RML) expressed in Pichia pastoris was investigated. To better understand the effect of glycosylation on the activity of RML, three mutants (M1, generated by N8A; M2, generated by N58A; and M3, generated by N8A and N58A) were designed to generate deglycosylated enzymes. The results showed that deglycosylated RML exhibited a twofold higher activity compared to the wild type. However, it was also found that glycosylation on the propeptide was important for the removal of the propeptide by Kex2 protease and secretion of the enzyme. Thus, our study provided a further understanding into the role of glycosylation on enzyme function.

Molecular mechanism and structural basis of interactions of dipeptidyl peptidase IV with adenosine deaminase and human immunodeficiency virus type-1 transcription transactivator

Dipeptidyl peptidase IV (DPPIV or CD26) is a multifunctional membrane glycoprotein. As an exopeptidase it regulates the activity of a series of biologically important peptides. Through its interaction with specific proteins and peptides, DPPIV is also involved in a wide range of biologically relevant processes such as cell adhesion, T cell activation and apoptosis. In this paper, we review our recent studies on the interactions of DPPIV with adenosine deaminase (ADA) and the transcription transactivator of the human immunodeficiency virus type-1 (HIV-1 Tat) as revealed by three-dimensional structure reconstructed by single particle analysis of cryo-electron microscopy (EM) and crystal structures of the human DPPIV-bovine ADA complex as well as the crystal structures of DPPIV in complex with HIV-1 Tat-derived nonapeptides. These results contribute importantly to the clarification of the molecular mechanisms of this multifunctional protein. The biological relevance of these interactions is discussed.

Upregulation of CD26 expression in epithelial cells and stromal cells during wound-induced skin tumour formation

We have previously described InvEE transgenic mice in which non-dividing, differentiating epidermal cells express oncogenically activated MAPK kinase 1 (MEK1). Skin wounding triggers tumour formation in InvEE mice via a mechanism that involves epidermal release of IL-1α and attraction of a pro-tumorigenic inflammatory infiltrate. To look for potential effects on the underlying connective tissue, we screened InvEE and wild-type epidermis for differential expression of cytokines and immune modulators. We identified a single protein, CD26 (dipeptidyl peptidase-4). CD26 serum levels were not increased in InvEE mice. In contrast, CD26 was upregulated in keratinocytes expressing mutant MEK1 and in the epithelial compartment of InvEE tumours, where it accumulated at cell-cell borders. CD26 expression was increased in dermal fibroblasts following skin wounding but was downregulated in tumour stroma. CD26 activity was stimulated by calcium-induced intercellular adhesion in keratinocytes, suggesting that the upregulation of CD26 in InvEE epidermis is due to expansion of the differentiated cell layers. IL-1α treatment of dermal fibroblasts stimulated CD26 activity, and therefore epidermal IL-1α release may contribute to the upregulation of CD26 expression in wounded dermis. Pharmacological blockade of CD26, via Sitagliptin, reduced growth of InvEE tumours, while combined inhibition of IL-1α and CD26 delayed tumour onset and reduced tumour incidence. Our results demonstrate that inappropriate activation of MEK1 in the epidermis leads to changes in dermal fibroblasts that, like the skin inflammatory infiltrate, contribute to tumour formation.

On the origin of serum CD26 and its altered concentration in cancer patients

Dipeptidyl peptidase IV (DPP-IV), assigned to the CD26 cluster, is expressed on epithelial cells and lymphocytes and is a multifunctional or pleiotropic protein. Its peptidase activity causes degradation of many biologically active peptides, e.g. some incretins secreted by the enteroendocrine system. DPP-IV has, therefore, become a novel therapeutic target for inhibitors that extend endogenously produced insulin half-life in diabetics, and several reviews have appeared in recent months concerning the clinical significance of CD26/DPP-IV. Biological fluids contain relatively high levels of soluble CD26 (sCD26). The physiological role of sCD26 and its relation, if any, to CD26 functions, remain poorly understood because whether the process for CD26 secretion and/or shedding from cell membranes is regulated or not is not known. Liver epithelium and lymphocytes are often cited as the most likely source of sCD26. It is important to establish which tissue or organ is the protein source as well as the circumstances that can provoke an abnormal presence/absence or altered levels in many diseases including cancer, so that sCD26 can be validated as a clinical marker or a therapeutic target. For example, we have previously reported low levels of sCD26 in the blood of colorectal cancer patients, which indicated the potential usefulness of the protein as a biomarker for this cancer in early diagnosis, monitoring and prognosis. Through this review, we envisage a role for sCD26 and the alteration of normal peptidase capacity (in clipping enteroendocrine or other peptides) in the complex crosstalk between the lymphoid lineage and, at least, some malignant tumours.

Histoplasma capsulatum encodes a dipeptidyl peptidase active against the mammalian immunoregulatory peptide, substance P

The pathogenic fungus Histoplasma capsulatum secretes dipeptidyl peptidase (Dpp) IV enzyme activity and has two putative DPPIV homologs (HcDPPIVA and HcDPPIVB). We previously showed that HcDPPIVB is the gene responsible for the majority of secreted DppIV activity in H. capsulatum culture supernatant, while we could not detect any functional contribution from HcDPPIVA. In order to determine whether HcDPPIVA encodes a functional DppIV enzyme, we expressed HcDPPIVA in Pichia pastoris and purified the recombinant protein. The recombinant enzyme cleaved synthetic DppIV substrates and had similar biochemical properties to other described DppIV enzymes, with temperature and pH optima of 42°C and 8, respectively. Recombinant HcDppIVA cleaved the host immunoregulatory peptide substance P, indicating the enzyme has the potential to affect the immune response during infection. Expression of HcDPPIVA under heterologous regulatory sequences in H. capsulatum resulted in increased secreted DppIV activity, indicating that the encoded protein can be expressed and secreted by its native organism. However, HcDPPIVA was not required for virulence in a murine model of histoplasmosis. This work reports a fungal enzyme that can function to cleave the immunomodulatory host peptide substance P.

Comprehensive genetic analysis of the dipeptidyl peptidase-4 gene and cardiovascular disease risk factors in obese individuals

The incretin system has been shown to stimulate insulin secretion in a glucose dependent manner and currently fosters considerable hope for the treatment of diabetes. Recently, we have shown that the dipeptidylpeptidase-4 (DPP4) gene, which is responsible for incretin inactivation, was overexpressed in omental adipose tissue of obese men with the metabolic syndrome, compared to men not characterized by this condition. Since the cardiovascular disease (CVD) risk profile shows substantial inter-individual variability in obesity, this study aimed at verifying whether DPP4 polymorphisms contribute to explain such a difference. In the first step of this multi-stage study, seven tagging SNPs were genotyped in a sample of 576 obese (BMI>40 kg/m(2)) individuals and tested for their association with blood pressure and lipids, as well as diabetes-related phenotypes. Then, in an additional sample of 572 obese individuals (stage 2), SNPs showing trends (P<0.10) for an association in the first sample were genotyped and reanalyzed. Logistic regressions were used to compute odds ratio for obesity-related metabolic complications. In sample 1, homozygotes for rs17848915 and rs7608798 minor alleles were at lower risk of hyperglycemia/diabetes (P=0.002) and elevated plasma triglyceride levels (P=0.030) respectively, whereas rs1558957 heterozygotes were at higher risk to have high plasma triglyceride (P=0.040), HDL- (P=0.021), LDL- (P=0.001) and total-cholesterol (P=0.003) levels. However, none of these associations was consistently replicated in stage 2. This first comprehensive genetic analysis does not support the notion that DPP4 polymorphisms could modulate the CVD risk profile among obese patients.

Highly fucosylated N-glycan ligands for mannan-binding protein expressed specifically on CD26 (DPPVI) isolated from a human colorectal carcinoma cell line, SW1116

The serum mannan-binding protein (MBP) is a host defense C-type lectin specific for mannose, N-acetylglucosamine, and fucose residues, and exhibits growth inhibitory activity toward human colorectal carcinoma cells. The MBP-ligand oligosaccharides (MLO) isolated from a human colorectal carcinoma cell line, SW1116, are large, multiantennary N-glycans with highly fucosylated polylactosamine-type structures having Le(b)-Le(a) or tandem repeats of the Le(a) structure at their nonreducing ends. In this study, we isolated the major MBP-ligand glycoproteins from SW1116 cell lysates with an MBP column and identified them as CD26/dipeptidyl peptidase IV (DPPIV) (110 kDa) and CD98 heavy chain (CD98hc)/4F2hc (82 kDa). Glycosidase digestion revealed that CD26 contained such complex-type N-glycans that appear to mediate the MBP binding. MALDI-MS of the N-glycans released from CD26 by PNGase F demonstrated conclusively that CD26 is the major MLO-carrying protein. More interestingly, a comparison of the N-glycans released from the MBP-binding and non-MBP-binding glycopeptides suggested that complex-type N-glycans carrying a minimum of 4 Le(a)/Le(b) epitopes arranged either as multimeric tandem repeats or terminal epitopes on multiantennary structures are critically important for the high affinity binding to MBP. Analysis of the N-glycan attachment sites demonstrated that the high affinity MLO was expressed preferentially at some N-glycosylation sites, but this site preference was not so stringent. Finally, hypothetical 3D models of tandem repeats of the Le(a) epitope and the MBP-Lewis oligosaccharide complex were presented.

Revisiting an old acquaintance: CD26 and its molecular mechanisms in T cell function

The role of CD26 in human T cell biology is puzzling. Despite being extensively characterized, it has been called 'a moonlighting protein' since it has multifunctional effects, but a definitive native ligand has not been identified. We summarize the current knowledge on the molecular mechanisms of CD26-mediated T cell costimulation and immune regulation. Work identifying a ligand for CD26 and elucidating the proximal signaling events associated with CD26-mediated T cell costimulation is also described. Finally, we discuss the involvement of CD26 in various pathophysiologic states as well as its suitability as a potential therapeutic target in selected immune diseases.

Corin is co-expressed with pro-ANP and localized on the cardiomyocyte surface in both zymogen and catalytically active forms

The multi-domain transmembrane serine protease corin cleaves pro-atrial natriuretic peptide (pro-ANP) in vitro to generate an active hormone, ANP. Corin may also contribute to the regulation of the natriuretic peptide system in vivo, and might be an attractive target for treatment of cardiovascular diseases. In order for corin to cleave its substrate pro-ANP, it should be catalytically active and located proximally. However, because knowledge of native corin is limited, we examined the expression, cardiac localization and molecular forms of the native corin protein. Immunofluorescence studies using a series of anti-corin antibodies directed against the stem and protease domains reveal that corin is present on the cell-surface of rat neonatal cardiomyocytes and murine HL-1 cardiomyocyte-like cells. Furthermore, we immunolocalized native corin in pro-ANP expressing cardiomyocytes. Immunoprecipitation of the membrane fraction of mouse heart extract showed that native corin had a relative mass of 205-210 kDa. Under reducing conditions native corin migrates as several different molecular weight forms corresponding to zymogen (uncleaved) and active (cleaved) forms. Studies using a FITC-tagged chloromethyl ketone that mimics the corin cleavage sequence in pro-ANP, suggest that an enzymatically active form of corin is localized to the cell surface of myocardial cells in vivo. Additionally, we showed that the 205-210 kDa form of corin is a glycosylated protein. Treatment of HL-1 cells with tunicamycin reduced the relative mass of expressed corin. We conclude that native corin is a glycosylated protease that is localized on the cell surface of pro-ANP-expressing cardiomyocytes in both zymogen and catalytically active forms.

Selective inhibition of fibroblast activation protein protease based on dipeptide substrate specificity

Fibroblast activation protein (FAP) is a transmembrane serine peptidase that belongs to the prolyl peptidase family. FAP has been implicated in cancer; however, its specific role remains elusive because inhibitors that distinguish FAP from other prolyl peptidases like dipeptidyl peptidase-4 (DPP-4) have not been developed. To identify peptide motifs for FAP-selective inhibitor design, we used P(2)-Pro(1) and acetyl (Ac)-P(2)-Pro(1) dipeptide substrate libraries, where P(2) was varied and substrate hydrolysis occurs between Pro(1) and a fluorescent leaving group. With the P(2)-Pro(1) library, FAP preferred Ile, Pro, or Arg at the P(2) residue; however, DPP-4 showed broad reactivity against this library, precluding selectivity. By contrast, with the Ac-P(2)-Pro(1) library, FAP cleaved only Ac-Gly-Pro, whereas DPP-4 showed little reactivity with all substrates. FAP also cleaved formyl-, benzyloxycarbonyl-, biotinyl-, and peptidyl-Gly-Pro substrates, which DPP-4 cleaved poorly, suggesting an N-acyl-Gly-Pro motif for inhibitor design. Therefore, we synthesized and tested the compound Ac-Gly-prolineboronic acid, which inhibited FAP with a K(i) of 23 +/- 3 nm. This was approximately 9- to approximately 5400-fold lower than the K(i) values for other prolyl peptidases, including DPP-4, DPP-7, DPP-8, DPP-9, prolyl oligopeptidase, and acylpeptide hydrolase. These results identify Ac-Gly-BoroPro as a FAP-selective inhibitor and suggest that N-acyl-Gly-Pro-based inhibitors will allow testing of FAP as a therapeutic target.

Identification and partial characterization of the enzyme of omega: one of five putative DPP IV genes in Drosophila melanogaster

The omega (ome) gene product is a modifier of larval cuticle protein 5 and its alleles (and duplicates) in the third instar of Drosophila melanogaster. Using deletion mapping the locus mapped to 70F-71A on the left arm of chromosome 3. A homozygote null mutant (ome 1) shows a pleiotropic phenotype that affected the size, developmental time of the flies, and the fertility (or perhaps the behavior) of homozygous mutant males. The omega gene was verified as producing a dipeptidyl peptidase IV (DPPIV) by genetic analysis, substrate specificity and pH optimum. The identity of the gene was confirmed as CG32145 (cytology 70F4) in the Celera Database (Berkeley Drosophila Genome Project), which is consistent with its deletion map position. The genomic structure of the gene is described and the decrease in DPPIV activity in the mutant ome1 is shown to be due to the gene CG32145 (omega). The D. melanogaster omega DPPIV enzyme was partially purified and characterized. The exons of the ome1 mutant were sequenced and a base substitution mutation in exon 4 was identified that would yield a truncated protein caused by a stop codon. A preliminary study of the compartmentalization of the omega DPPIV enzyme in several organs is also reported.

Hierarchical Regulation of CTLA-4 Dimer-Based Lattice Formation and Its Biological Relevance for T Cell Inactivation

CTLA-4 is an activation-induced, homodimeric inhibitory receptor in T cells. Recent crystallographic reports have suggested that it may form lattice-like arrays on the cell surface upon binding B7.1/B7.2 (CD80, CD86) molecules. To test the biological relevance of these CTLA-4-B7 lattices, we introduced a C122A point mutation in human CTLA-4, because this residue was shown to be essential for dimerization in solution. Surprisingly, we found that up to 35% of C122A CTLA-4 dimerized in human T lymphocytes. Moreover, C122A CTLA-4 partitioned within lipid rafts, colocalized with the TCR in the immunological synapse, and inhibited T cell activation. C122-independent dimerization of CTLA-4 involved N-glycosylation, because further mutation of the N78 and N110 glycosylation sites abrogated dimerization. Despite being monomeric, the N78A/N110A/C122A triple mutant CTLA-4 localized in the immunological synapse and inhibited T cell activation. Such functionality correlated with B7-induced dimerization of these mutant molecules. Based on these data, we propose a model of hierarchical regulation of CTLA-4 oligomerization by which B7 binding ultimately determines the formation of dimer-dependent CTLA-4 lattices that may be necessary for triggering B7-dependent T cell inactivation.

Survey of the year 2004 commercial optical biosensor literature

The year 2004 represents a milestone for the biosensor research community: in this year, over 1000 articles were published describing experiments performed using commercially available systems. The 1038 papers we found represent an approximately 10% increase over the past year and demonstrate that the implementation of biosensors continues to expand at a healthy pace. We evaluated the data presented in each paper and compiled a 'top 10' list. These 10 articles, which we recommend every biosensor user reads, describe well-performed kinetic, equilibrium and qualitative/screening studies, provide comparisons between binding parameters obtained from different biosensor users, as well as from biosensor- and solution-based interaction analyses, and summarize the cutting-edge applications of the technology. We also re-iterate some of the experimental pitfalls that lead to sub-optimal data and over-interpreted results. We are hopeful that the biosensor community, by applying the hints we outline, will obtain data on a par with that presented in the 10 spotlighted articles. This will ensure that the scientific community at large can be confident in the data we report from optical biosensors.

Crystal structure of CD26/dipeptidyl-peptidase IV in complex with adenosine deaminase reveals a highly amphiphilic interface

Dipeptidyl-peptidase IV (DPPIV or CD26) is a homodimeric type II membrane glycoprotein in which the two monomers are subdivided into a beta-propeller domain and an alpha/beta-hydrolase domain. As dipeptidase, DPPIV modulates the activity of various biologically important peptides and, in addition, DPPIV acts as a receptor for adenosine deaminase (ADA), thereby mediating co-stimulatory signals in T-lymphocytes. The 3.0-A resolution crystal structure of the complex formed between human DPPIV and bovine ADA presented here shows that each beta-propeller domain of the DPPIV dimer binds one ADA. At the binding interface, two hydrophobic loops protruding from the beta-propeller domain of DPPIV interact with two hydrophilic and heavily charged alpha-helices of ADA, giving rise to the highest percentage of charged residues involved in a protein-protein contact reported thus far. Additionally, four glycosides linked to Asn229 of DPPIV bind to ADA. In the crystal structure of porcine DPPIV, the observed tetramer formation was suggested to mediate epithelial and lymphocyte cell-cell adhesion. ADA binding to DPPIV could regulate this adhesion, as it would abolish tetramerization.

Crystal structure of human dipeptidyl peptidase IV in complex with a decapeptide reveals details on substrate specificity and tetrahedral intermediate formation

Dipeptidyl peptidase IV (DPPIV) is a member of the prolyl oligopeptidase family of serine proteases. DPPIV removes dipeptides from the N terminus of substrates, including many chemokines, neuropeptides, and peptide hormones. Specific inhibition of DPPIV is being investigated in human trials for the treatment of type II diabetes. To understand better the molecular determinants that underlie enzyme catalysis and substrate specificity, we report the crystal structures of DPPIV in the free form and in complex with the first 10 residues of the physiological substrate, Neuropeptide Y (residues 1-10; tNPY). The crystal structure of the free form of the enzyme reveals two potential channels through which substrates could access the active site-a so-called propeller opening, and side opening. The crystal structure of the DPPIV/tNPY complex suggests that bioactive peptides utilize the side opening unique to DPPIV to access the active site. Other structural features in the active site such as the presence of a Glu motif, a well-defined hydrophobic S1 subsite, and minimal long-range interactions explain the substrate recognition and binding properties of DPPIV. Moreover, in the DPPIV/tNPY complex structure, the peptide is not cleaved but trapped in a tetrahedral intermediate that occurs during catalysis. Conformational changes of S630 and H740 between DPPIV in its free form and in complex with tNPY were observed and contribute to the stabilization of the tetrahedral intermediate. Our results facilitate the design of potent, selective small molecule inhibitors of DPPIV that may yield compounds for the development of novel drugs to treat type II diabetes.