Progress in metallocarboxypeptidases and their small molecular weight inhibitors

Modular Design Platform for Activatable Fluorescence Probes Targeting Carboxypeptidases Based on ProTide Chemistry

Carboxypeptidases (CPs) are a family of hydrolases that cleave one or more amino acids from the C-terminal of peptides or proteins and play indispensable roles in various physiological and pathological processes. However, only a few highly activatable fluorescence probes for CPs have been reported, and there is a need for a flexibly tunable molecular design platform to afford a range of fluorescence probes for CPs for biological and medical research. Here, we focused on the unique activation mechanism of ProTide-based prodrugs and established a modular design platform for CP-targeting florescence probes based on ProTide chemistry. In this design, probe properties such as fluorescence emission wavelength, reactivity/stability, and target CP can be readily tuned and optimized by changing the four probe modules: the fluorophore, the substituent on the phosphorus atom, the linker amino acid at the P1 position, and the substrate amino acid at the P1' position. In particular, switching the linker amino acid at position P1 enabled us to precisely optimize the reactivity for target CPs. As a proof-of-concept, we constructed probes for carboxypeptidase M (CPM) and prostate-specific membrane antigen (also known as glutamate carboxypeptidase II). The developed probes were applicable for the imaging of CP activities in live cells and in clinical specimens from patients. This design strategy should be useful in studying CP-related biological and pathological phenomena.

Analysis of the mast cell expressed carboxypeptidase A3 and its structural and evolutionary relationship to other vertebrate carboxypeptidases

Metallo-carboxypeptidases are exopeptidases with diverse expression and function, found in all kingdoms of life from bacteria to mammals. One of them, the carboxypeptidase A3 (CPA3), has become an important component of the mammalian immune system by its expression in mast cells. Mast cells (MCs) are highly specialized sentinel cells, which store large amounts of bioactive mediators, including CPA3, in very abundant cytoplasmic granules. Clinical studies have found an increased CPA3 expression in asthma but the physiological role as well as the evolutionary origin of CPA3 remains largely unexplored. CPA3 belongs to the M14A subfamily of metallo-carboxypeptidases, which among others also includes the digestive enzymes CPA1, CPA2, CPB1 and CPO. To study the appearance of CPA3 during vertebrate evolution, we here performed bioinformatic analyses of homologous genes and gene loci from a broad panel of metazoan animals from invertebrates to mammals. The phylogenetic analysis indicated that CPA3 appeared at the base of tetrapod evolution in a branch closer to CPB1 than to other CPAs. Indeed, CPA3 and CPB1 are also located in the same locus, on chromosome 3 in humans. The presence of CPA3 only in tetrapods and not in fishes, suggested that CPA3 could have appeared by a gene duplication from CPB1 during early tetrapod evolution. However, the apparent loss of CPA3 in several tetrapod lineages, e.g. in birds and monotremes, indicates a complex evolution of the CPA3 gene. Interestingly, in the lack of CPA3 in fishes, zebrafish MCs express instead CPA5 for which the most closely related human carboxypeptidase is CPA1, which has a similar cleavage specificity as CPA3. Collectively, these findings clarify and add to our understanding of the evolution of hematopoietic proteases expressed by mast cells.

Fluorescence Probes for Imaging Basic Carboxypeptidase Activity in Living Cells with High Intracellular Retention

Basic carboxypeptidases (basic CPs) cleave the C-terminal basic amino acid of peptides, and their activity is upregulated in some types of cancers. Therefore, detecting the activity of basic CPs in living cells would be important not only for studying the physiological functions of these enzymes but also for visualization of cancerous tissues. Here, we report two fluorescein diacetate (FDA)-based activatable fluorescence probes, named 5ArgAF-FDA and 5LysAF-FDA, in which the substrate amino acid arginine or lysine is conjugated to the benzene moiety via an azoformyl linker. In live-cell fluorescence imaging of CPM, one of the seven basic CPs, 5ArgAF-FDA showed a larger intracellular fluorescence increase than did 5LysAF-FDA within a few minutes. This increase was inhibited by coincubation with 2-mercaptomethyl-3-guanidinoethylthiopropanoic acid (MGTA), an inhibitor of basic CPs. When 5ArgAF-FDA was applied to a coculture of two breast cancer cell lines with different CPM activities, the fluorescence increase in individual cells was correlated with the expression level of CPM, suggesting that 5ArgAF-FDA has the ability to distinguish cell lines having different levels of CPM activity, owing to its high intracellular retention. We believe these probes will be useful for imaging cancers with upregulated basic CP activity.

Recent Progress in Small Spirocyclic, Xanthene-Based Fluorescent Probes

The use of fluorescent probes in a multitude of applications is still an expanding field. This review covers the recent progress made in small molecular, spirocyclic xanthene-based probes containing different heteroatoms (e.g., oxygen, silicon, carbon) in position 10'. After a short introduction, we will focus on applications like the interaction of probes with enzymes and targeted labeling of organelles and proteins, detection of small molecules, as well as their use in therapeutics or diagnostics and super-resolution microscopy. Furthermore, the last part will summarize recent advances in the synthesis and understanding of their structure-behavior relationship including novel computational approaches.

Overexpression of carboxypeptidase X M14 family member 2 predicts an unfavorable prognosis and promotes proliferation and migration of osteosarcoma

Background

Carboxypeptidase X, M14 family member 2 (CPXM2), has been associated with several human developmental disorders. However, whether CPXM2 is involved in oncogenesis or tumor progression remains unclear. Currently, the clinical relevance and function of CPXM2 in human osteosarcoma were investigated.

Materials and methods

The expression of CPXM2 in osteosarcoma cell lines and tissues were explored by immunohistochemistry and western blotting assays. A eukaryotic expression plasmid was transfected into fetal osteoblast cells to overexpress CPXM2 and the endogenous CPXM2 in osteosarcoma cells was silenced through an RNA interference (RNAi) method transfection. These transfections were validated via western blotting, and the expression levels of several key molecules involved in the epithelial mesenchymal transition was also determined via western blotting. The expression levels of CPXM2 in a fetal osteoblast cell line with CPXM2 overexpressing and an osteosarcoma CPXM2-knockout cell line was confirmed via reverse transcription-quantitative polymerase chain reaction (RT-qPCR), western blotting and immunofluorescence. The malignant phenotype of osteosarcoma cells was indicated by the cholecystokinin octapeptide, colony formation assay, scratch wound healing assay, and Transwell® migration assay.

Results

We found that CPXM2 was overexpressed in osteosarcoma and that the overexpression was associated with an unfavorable prognosis and tumor node metastasis staging. The knockdown of CPXM2 in cultured osteosarcoma cells significantly impeded cell proliferation and migration. In addition, the upregulation of CPXM2 in fetal osteoblast cells significantly promoted cell proliferation and migration. Besides, western blotting results revealed that several key molecules involved in the epithelial mesenchymal transition (EMT) were regulated by CPXM2.

Conclusion

Taken together, these results imply an active role for CPXM2 in promoting tumor aggressiveness via epithelial to mesenchymal transition (EMT) modulation in osteosarcoma.

Characterization, Recombinant Production and Structure-Function Analysis of NvCI, A Picomolar Metallocarboxypeptidase Inhibitor from the Marine Snail Nerita versicolor

A very powerful proteinaceous inhibitor of metallocarboxypeptidases has been isolated from the marine snail Nerita versicolor and characterized in depth. The most abundant of four, very similar isoforms, NvCla, was taken as reference and N-terminally sequenced to obtain a 372-nucleotide band coding for the protein cDNA. The mature protein contains 53 residues and three disulphide bonds. NvCIa and the other isoforms show an exceptionally high inhibitory capacity of around 1.8 pM for human Carboxypeptidase A1 (hCPA1) and for other A-like members of the M14 CPA subfamily, whereas a twofold decrease in inhibitory potency is observed for carboxypeptidase B-like members as hCPB and hTAFIa. A recombinant form, rNvCI, was produced in high yield and HPLC, mass spectrometry and spectroscopic analyses by CD and NMR indicated its homogeneous, compact and thermally resistant nature. Using antibodies raised with rNvCI and histochemical analyses, a preferential distribution of the inhibitor in the surface regions of the animal body was observed, particularly nearby the open entrance of the shell and gut, suggesting its involvement in biological defense mechanisms. The properties of this strong, small and stable inhibitor of metallocarboxypeptidases envisage potentialities for its direct applicability, as well as leading or minimized forms, in biotechnological/biomedical uses.

Overexpression of CPXM2 predicts an unfavorable prognosis and promotes the proliferation and migration of gastric cancer

Carboxypeptidase X, M14 family member 2 (CPXM2), has been associated with several human disorders such as developmental diseases. However, whether CPXM2 is involved in oncogenesis or tumor progression remains unclear. In the present study, we used clinical samples from gastric cancer (GC) patients to investigate potential roles of CPXM2 in GC. We also analyzed datasets from the Oncomine database, The Cancer Genome Atlas (TCGA), and the Kaplan‑Meier Plotter to validate these results. We found that CPXM2 was overexpressed in GC and that the overexpression was associated with an unfavorable prognosis, regardless of the Lauren classification and tumor node metastasis staging. In addition, knockdown of CPXM2 in cultured GC cells significantly impeded cell proliferation and migration, as indicated by the cholecystokinin octapeptide, colony formation assay, scratch wound healing assay, and Transwell® migration assay. Furthermore, gene set enrichment analysis using RNA‑seq data from TCGA indicated that high CPXM2 expression in GC patients was positively correlated with the HALLMARK_APICAL_JUNCTION and HALLMARK_EPITHELIAL_MESENCHYMAL_TRANSITION gene sets. Finally, western blotting results revealed that several key molecules involved in the epithelial mesenchymal transition were regulated by CPXM2. Taken together, these results imply an active role for CPXM2 in promoting tumor aggressiveness via epithelial to mesenchymal transition (EMT) modulation in GCs.

Synthesis and Structural/Functional Characterization of Selective M14 Metallocarboxypeptidase Inhibitors Based on Phosphinic Pseudopeptide Scaffold: Implications on the Design of Specific Optical Probes

Metallocarboxypeptidases (MCPs) of the M14 family are Zn²⁺-dependent exoproteases present in almost every tissue or fluid in mammals. These enzymes perform a large variety of physiological functions and are involved in several pathologies, such as pancreatic diseases, inflammation, fibrinolysis, and cancer. Here, we describe the synthesis and functional/structural characterization of a series of reversible tight-binding phosphinic pseudopeptide inhibitors that show high specificity and potency toward these proteases. Characterization of their inhibitory potential against a large variety of MCPs, combined with high-resolution crystal structures of three selected candidates in complex with human carboxypeptidase A (CPA)1, allowed to decipher the structural determinants governing selectivity for type-A of the M14A MCP family. Further, the phosphinic pseudopeptide framework was exploited to generate an optical probe selectively targeting human CPAs. The phosphinic pseudopeptides presented here constitute the first example of chemical probes useful to selectively report on type-A MCPs activity in complex media.

Carboxypeptidase O is a lipid droplet-associated enzyme able to cleave both acidic and polar C-terminal amino acids

Carboxypeptidase O (CPO) is a member of the M14 family of metallocarboxypeptidases with a preference for the cleavage of C-terminal acidic amino acids. CPO is largely expressed in the small intestine, although it has been detected in other tissues such as the brain and ovaries. CPO does not contain a prodomain, nor is it strongly regulated by pH, and hence appears to exist as a constitutively active enzyme. The goal of this study was to investigate the intracellular distribution and activity of CPO in order to predict physiological substrates and function. The distribution of CPO, when expressed in MDCK cells, was analyzed by immunofluorescence microscopy. Soon after addition of nutrient-rich media, CPO was found to associate with lipid droplets, causing an increase in lipid droplet quantity. As media became depleted, CPO moved to a broader ER distribution, no longer impacting lipid droplet numbers. Membrane cholesterol levels played a role in the distribution and in vitro enzymatic activity of CPO, with cholesterol enrichment leading to decreased lipid droplet association and enzymatic activity. The ability of CPO to cleave C-terminal amino acids within the early secretory pathway (in vivo) was examined using Gaussia luciferase as a substrate, C-terminally tagged with variants of an ER retention signal. While no effect of cholesterol was observed, these data show that CPO does function as an active enzyme within the ER where it removes C-terminal glutamates and aspartates, as well as a number of polar amino acids.

Crystal structure and mechanism of human carboxypeptidase O: Insights into its specific activity for acidic residues

Human metallocarboxypeptidase O (hCPO) is a recently discovered digestive enzyme localized to the apical membrane of intestinal epithelial cells. Unlike pancreatic metallocarboxypeptidases, hCPO is glycosylated and produced as an active enzyme with distinctive substrate specificity toward C-terminal (C-t) acidic residues. Here we present the crystal structure of hCPO at 1.85-Å resolution, both alone and in complex with a carboxypeptidase inhibitor (NvCI) from the marine snail Nerita versicolor The structure provides detailed information regarding determinants of enzyme specificity, in particular Arg275, placed at the bottom of the substrate-binding pocket. This residue, located at "canonical" position 255, where it is Ile in human pancreatic carboxypeptidases A1 (hCPA1) and A2 (hCPA2) and Asp in B (hCPB), plays a dominant role in determining the preference of hCPO for acidic C-t residues. Site-directed mutagenesis to Asp and Ala changes the specificity to C-t basic and hydrophobic residues, respectively. The single-site mutants thus faithfully mimic the enzymatic properties of CPB and CPA, respectively. hCPO also shows a preference for Glu over Asp, probably as a consequence of a tighter fitting of the Glu side chain in its S1' substrate-binding pocket. This unique preference of hCPO, together with hCPA1, hCPA2, and hCPB, completes the array of C-t cleavages enabling the digestion of the dietary proteins within the intestine. Finally, in addition to activity toward small synthetic substrates and peptides, hCPO can also trim C-t extensions of proteins, such as epidermal growth factor, suggesting a role in the maturation and degradation of growth factors and bioactive peptides.

Proteomics and 1H NMR-based metabolomics analysis of pathogenic Vibrio vulnificus aquacultures isolated from sewage drains

Vibrio bacteria live in both marine and freshwater habitats and are associated with aquatic animals. Vibrio vulnificus is a pathogenic bacterium that infects people and livestock. It is usually found in offshore waters or within fish and shellfish. This study presents a comparative proteomic analysis of the outer membrane protein (OMP) changes in V. vulnificus proteins after stimulation with sewage from sewage drains. Using two-dimensional electrophoresis followed by MALDI-TOF MS/MS, 32 protein spots with significant differences in abundance were identified and characterized. These identified proteins were found to be involved in various functional categories, including catalysis, transport, membrane proteins progresses, receptor activity, energy metabolism, cytokine activity, and protein metabolism. The mRNA expression levels of 12 differential proteins were further assessed by qRT-PCR. Seven genes including carboxypeptidase, hemoglobin receptor, succinate dehydrogenase iron-sulfur subunit, ATP synthase subunit alpha, thioredoxin, succinyl-CoA synthetase subunit, and alanine dehydrogenase were downregulated upon stimulation, whereas the protein expression levels HupA receptor, type I secretion outer membrane protein, glutamine synthetase, superoxide dismutase, OmpU, and VuuA were upregulated. ¹H NMR spectra showed 18 dysregulated metabolites from V. vulnificus after the sewage stimulation and the pathogenicity was enhanced after that.

Exploring secondary-sphere interactions in Fe-N x H y complexes relevant to N2 fixation

Hydrogen bonding and other types of secondary-sphere interactions are ubiquitous in metalloenzyme active sites and are critical to the transformations they mediate. Exploiting secondary sphere interactions in synthetic catalysts to study the role(s) they might play in biological systems, and to develop increasingly efficient catalysts, is an important challenge. Whereas model studies in this broad context are increasingly abundant, as yet there has been relatively little progress in the area of synthetic catalysts for nitrogen fixation that incorporate secondary sphere design elements. Herein we present our first study of Fe-N x H y complexes supported by new tris(phosphine)silyl ligands, abbreviated as [SiPNMe3] and [SiPiPr2PNMe], that incorporate remote tertiary amine hydrogen-bond acceptors within a tertiary phosphine/amine 6-membered ring. These remote amine sites facilitate hydrogen-bonding interactions via a boat conformation of the 6-membered ring when certain nitrogenous substrates (e.g., NH3 and N2H4) are coordinated to the apical site of a trigonal bipyramidal iron complex, and adopt a chair conformation when no H-bonding is possible (e.g., N2). Countercation binding at the cyclic amine is also observed for anionic {Fe-N2}- complexes. Reactivity studies in the presence of proton/electron sources show that the incorporated amine functionality leads to rapid generation of catalytically inactive Fe-H species, thereby substantiating a hydride termination pathway that we have previously proposed deactivates catalysts of the type [EPR3]FeN2 (E = Si, C).

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.

Variation at HLA-DPB1 is associated with dermatomyositis in Chinese population

Dermatomyositis (DM) is a polygenic disorder characterized by inflammation of skeletal muscle and skin. To date, the exact etiopathogenesis of DM remains elusive. To explore the genetic basis of DM, we conducted genome-wide genotyping analysis of 127 patients and 1566 healthy controls by Illumina Human OmniZhongHua-8 BeadChips in the Chinese Han population. We investigated whether the three SNP (rs7750458, rs9501251 and rs9500928) at 6p21.32 in the HLA-DPB1 gene were significantly associated with DM (P < 5 × 10^-8 ) and identified two susceptibility loci at 7q34 (PIP, rs9986765, P = 7.45 × 10^-7 , odds ratio [OR] = 2.71) and 10q24.2 (CPN1, rs3750716, P = 9.04 × 10^-7 , OR = 4.39) with suggestive evidence. We imputed 6674 classical human leukocyte antigen (HLA) alleles, amino acids and SNP from the discovery dataset, and stepwise analysis revealed that HLA-DPB1*17 in class II HLA genes were significantly associated with DM susceptibility. This study represents the first genome-wide association study (GWAS) of DM in the Chinese Han population. For the first time, HLA-DPB1 was found to be associated with DM in this population. Moreover, we identified two novel suggestive susceptibility loci (PIP and CPN1) and confirmed four previously reported genes (DMB, DQA1, DQB1 and DRB1) having potential associations with DM in the Chinese Han population. Our GWAS results in this population should provide important information regarding the genetic etiopathogenesis of DM and facilitate the development of new therapies for the treatment of DM and the prevention of DM progression.

Amyloid formation by human carboxypeptidase D transthyretin-like domain under physiological conditions

Protein aggregation is linked to a growing list of diseases, but it is also an intrinsic property of polypeptides, because the formation of functional globular proteins comes at the expense of an inherent aggregation propensity. Certain proteins can access aggregation-prone states from native-like conformations without the need to cross the energy barrier for unfolding. This is the case of transthyretin (TTR), a homotetrameric protein whose dissociation into its monomers initiates the aggregation cascade. Domains with structural homology to TTR exist in a number of proteins, including the M14B subfamily carboxypeptidases. We show here that the monomeric transthyretin-like domain of human carboxypeptidase D aggregates under close to physiological conditions into amyloid structures, with the population of folded but aggregation-prone states being controlled by the conformational stability of the domain. We thus confirm that the TTR fold keeps a generic residual aggregation propensity upon folding, resulting from the presence of preformed amyloidogenic β-strands in the native state. These structural elements should serve for functional/structural purposes, because they have not been purged out by evolution, but at the same time they put proteins like carboxypeptidase D at risk of aggregation in biological environments and thus can potentially lead to deposition diseases.

Carboxyterminal protein processing in health and disease: key actors and emerging technologies

Carboxypeptidases are important mediators of cellular behavior. Through C-terminal truncations, they alter protein functionality and participate in proteome turnover. Similarly, carboxypeptidases shape the human peptidome by targeting neuroendocrine and vasoactive peptides, thereby regulating signaling pathways in the nervous and cardiovascular systems as well as in embryonic development. Carboxypeptidases are widely connected to various pathological processes such as carcinogenesis and neurodegenerative and cardiovascular diseases. The repertoire of carboxypeptidase in vivo substrates still remains poorly defined, largely due to the lack of suitable experimental approaches. Understanding the precise role of carboxypeptidases is pivotal in the future development of diagnostic/prognostic markers in such diseases. To date, very little attention has been paid to the implication of carboxypeptidases in shaping the proteome as well as the peptidome. This review focuses on the patho-physiological function of carboxypeptidases and highlights the approaches by which proteomics-based technologies can be applied to characterize carboxypeptidases and to quantify the differential regulation of proteins by carboxypeptidases in a proteome-wide manner.

A functional and structural study of the major metalloprotease secreted by the pathogenic fungusAspergillus fumigatus

Fungalysins are secreted fungal peptidases with the ability to degrade the extracellular matrix proteins elastin and collagen and are thought to act as virulence factors in diseases caused by fungi. Fungalysins constitute a unique family among zinc-dependent peptidases that bears low sequence similarity to known bacterial peptidases of the thermolysin family. The crystal structure of the archetype of the fungalysin family,Aspergillus fumigatusmetalloprotease (AfuMep), has been obtained for the first time. The 1.8 Å resolution structure of AfuMep corresponds to that of an autoproteolyzed proenzyme with separate polypeptide chains corresponding to the N-terminal prodomain in a binary complex with the C-terminal zinc-bound catalytic domain. The prodomain consists of a tandem of cystatin-like folds whose C-terminal end is buried into the active-site cleft of the catalytic domain. The catalytic domain harbouring the key catalytic zinc ion and its ligands, two histidines and one glutamic acid, undergoes a conspicuous rearrangement of its N-terminal end during maturation. One key positively charged amino-acid residue and the C-terminal disulfide bridge appear to contribute to its structural–functional properties. Thus, structural, biophysical and biochemical analysis were combined to provide a deeper comprehension of the underlying properties ofA. fumigatusfungalysin, serving as a framework for the as yet poorly known metallopeptidases from pathogenic fungi.

Insights into thrombin activatable fibrinolysis inhibitor function and regulation

Fibrinolysis is initiated when the zymogen plasminogen is converted to plasmin via the action of plasminogen activators. Proteolytic cleavage of fibrin by plasmin generates C-terminal lysine residues capable of binding both plasminogen and the plasminogen activator, thereby stimulating plasminogen activator-mediated plasminogen activation and propagating fibrinolysis. This positive feedback mechanism is regulated by activated thrombin activatable fibrinolysis inhibitor (TAFIa), which cleaves C-terminal lysine residues from the fibrin surface, thereby decreasing its cofactor activity. TAFI can be activated by thrombin alone, but the rate of activation is accelerated when in complex with thrombomodulin. Plasmin is also known to activate TAFI. TAFIa has no known physiologic inhibitors and consequently, its primary regulatory mechanism involves its intrinsic thermal instability. The rate of TAFI activation and stability of the active form, TAFIa, function in maintaining its concentration above the threshold value required to down-regulate fibrinolysis. Although all methods to quantify TAFI or TAFIa have their limitations, epidemiologic studies have indicated that elevated TAFI levels are correlated with an increased risk of venous thrombosis. Major efforts have been made to develop TAFI inhibitors that can either directly interfere with TAFIa activity or impair its activation. However, the anti-inflammatory properties of TAFIa might complicate the development and application of a TAFIa inhibitor that aims to increase the efficiency of thrombolytic therapy.

The potential of carboxypeptidase M as a therapeutic target in cancer

INTRODUCTION

In the recent literature, carboxypeptidase M (CPM) emerged as a potential cancer biomarker. CPM modulates receptor signaling of kinins, anaphylatoxins, and chemokines. These CPM substrates affect proliferation, angiogenesis, and apoptosis of cancer cells. What is the evidence that CPM is a drug target for cancer therapy?

AREAS COVERED

The literature was searched using PubMed with the search terms "carboxypeptidase M" and/or "chromosome 12q13-15" eventually combined with general terms related to cancer. Information was retrieved from the GEO database and material of gene expression and proteomic studies.

EXPERT OPINION

CPM is a part of the molecular signature of many cancers. There is good evidence that it is useful for the discrimination and stratification of cancer types, possibly in combination with other markers such as EGFR and MDM2. Whether it is also a drug target remains to be determined. Lung, kidney, brain, and the reproductive system contain relatively high levels of CPM, but its functions in those tissues are largely unknown. CPM is expressed on tumor-associated macrophages. To facilitate the investigation of CPM in tumor-associated inflammation and in the other aspects of tumor biology, it is necessary to develop potent and selective CPM inhibitors.

Deletion of carboxypeptidase N delays onset of experimental cerebral malaria

Complement contributes to inflammation during pathogen infections; however, less is known regarding its role during malaria and in the severest form of the disease, cerebral malaria. Recent studies have shown that deletion of the complement anaphylatoxins receptors, C3aR and C5aR, does not alter disease susceptibility in experimental cerebral malaria (ECM). This does not, however, preclude C3a- and C5a-mediated contributions to inflammation in ECM and raises the possibility that carboxypeptidase regulation of anaphylatoxin activity rapidly over rides their functions. To address this question, we performed ECM using carboxypeptidase N-deficient (CPN(-/-)) mice. Unexpectedly, we found that CPN(-/-) mice survived longer than wild-type mice, but they were fully susceptible to ECM. CD4(+) and CD8(+) T cell infiltration was not reduced at the peak of disease in CPN(-/-) mice, and there was no corresponding reduction in pro-inflammatory cytokine production. Our results indicate that carboxypeptidases contribute to the pathogenesis of ECM and that studies examining the contribution of other carboxypeptidase families and family members may provide greater insight into the role these enzymes play in malaria.

Parasite neuropeptide biology: Seeding rational drug target selection?

The rationale for identifying drug targets within helminth neuromuscular signalling systems is based on the premise that adequate nerve and muscle function is essential for many of the key behavioural determinants of helminth parasitism, including sensory perception/host location, invasion, locomotion/orientation, attachment, feeding and reproduction. This premise is validated by the tendency of current anthelmintics to act on classical neurotransmitter-gated ion channels present on helminth nerve and/or muscle, yielding therapeutic endpoints associated with paralysis and/or death. Supplementary to classical neurotransmitters, helminth nervous systems are peptide-rich and encompass associated biosynthetic and signal transduction components - putative drug targets that remain to be exploited by anthelmintic chemotherapy. At this time, no neuropeptide system-targeting lead compounds have been reported, and given that our basic knowledge of neuropeptide biology in parasitic helminths remains inadequate, the short-term prospects for such drugs remain poor. Here, we review current knowledge of neuropeptide signalling in Nematoda and Platyhelminthes, and highlight a suite of 19 protein families that yield deleterious phenotypes in helminth reverse genetics screens. We suggest that orthologues of some of these peptidergic signalling components represent appealing therapeutic targets in parasitic helminths.

Molecular dynamics and free energy studies on the carboxypeptidases complexed with peptide/small molecular inhibitor: mechanism for drug resistance

As one potent plant protease inhibitor, potato carboxypeptidase inhibitor (PCI) can competitively inhibit insect digestive metallocarboxypeptidases (MCPs) through interfering with its digestive system that causes amino acid deficiencies and leading to serious developmental delay and mortality. However, this effective biological pest control is significantly impaired by the PCI-resistant insect MCPs. Therefore, deep understanding of the resistant mechanism of insect MCPs is particularly necessary for designing new durable pest control regimen and developing effective pesticides. In this study, the binding of PCI and small molecular inhibitor THI to insect PCI-sensitive/-resistant MCPs and human MCP was investigated by docking, molecular dynamics (MD) simulations and thermodynamic analysis. The structural analysis from MD simulations indicates that the PCI-resistant mechanism of CPBHz is mainly dominated by the Trp277A, which changes the conformation of β8-α9 loop and therefore narrow the access to the active site of CPBHz, prohibiting the entrance of the C termini tail of PCI. Additionally, the insertion of Gly247A weakens the stabilization of CPBHz and PCI through disrupting the hydrogen bond formation with its surrounding residues. Furthermore, the predicted binding free energies gives explanation of structure affinity relationship of PCI and THI with MCPs and suggest that the electrostatic energy is the main contribution term affecting the difference in binding affinities. Finally, the decomposition analysis of binding free energies infers that the key residues Glu72, Arg127, Ile247/Leu247 and Glu270 are critical for the binding of PCI/THI to MCPs.

Intravenous and oral administrations of DD2 [7-Amino-2-(sulfanylmethyl)heptanoic acid] produce thrombolysis through inhibition of plasma TAFIa in rats with tissue factor-induced microthrombosis

Thrombin-activatable fibrinolysis inhibitor (TAFI) is a plasma zymogen that is activated by thrombin in plasma. In fibrinolytic processes, carboxy-terminal lysine (Lys) residues in partially degraded fibrin are important sites for plasminogen binding and activation, and an active form of TAFI (TAFIa) inhibits fibrinolysis by eliminating these residues proteolytically. We synthesized DD2 [7-Amino-2-(sulfanylmethyl)heptanoic acid], a Lys analogue containing sulfur, as an inhibitor of TAFIa and investigated its pharmacological profile and pathophysiological role in thrombolysis via in vitro and in vivo studies. DD2 specifically inhibited plasma TAFIa activity with an apparent IC(50) (50% inhibitory concentration) value of 3.4×10(-8)M under the present experimental condition and enhanced tissue plasminogen activator-mediated clot lysis in a concentration-dependent manner. In order to study tissue factor (TF)-induced microthrombosis in an animal model, rats were given intravenous injection (2.5mg/kg and higher) or oral administration (10mg/kg and higher) of DD2. This attenuated TF-induced glomerular fibrin deposition and increased the plasma levels of fibrin degradation products and D-dimer in a dose-dependent manner. A DD2 dose approximately 4X higher than the dose used in intravenous injections was required to achieve an equivalent thrombolytic effect to that seen following oral administration. Moreover, the oral absorption efficiency of DD2 into the vasculature was 29.8%. These results indicate that both intravenous and oral administration of DD2 enhanced endogenous fibrinolysis and reduced thrombi in a TF-induced microthrombosis model.

Carboxypeptidase O is a glycosylphosphatidylinositol-anchored intestinal peptidase with acidic amino acid specificity

The first metallocarboxypeptidase (CP) was identified in pancreatic extracts more than 80 years ago and named carboxypeptidase A (CPA; now known as CPA1). Since that time, seven additional mammalian members of the CPA subfamily have been described, all of which are initially produced as proenzymes, are activated by endoproteases, and remove either C-terminal hydrophobic or basic amino acids from peptides. Here we describe the enzymatic and structural properties of carboxypeptidase O (CPO), a previously uncharacterized and unique member of the CPA subfamily. Whereas all other members of the CPA subfamily contain an N-terminal prodomain necessary for folding, bioinformatics and expression of both human and zebrafish CPO orthologs revealed that CPO does not require a prodomain. CPO was purified by affinity chromatography, and the purified enzyme was able to cleave proteins and synthetic peptides with greatest activity toward acidic C-terminal amino acids unlike other CPA-like enzymes. CPO displayed a neutral pH optimum and was inhibited by common metallocarboxypeptidase inhibitors as well as citrate. CPO was modified by attachment of a glycosylphosphatidylinositol membrane anchor to the C terminus of the protein. Immunocytochemistry of Madin-Darby canine kidney cells stably expressing CPO showed localization to vesicular membranes in subconfluent cells and to the plasma membrane in differentiated cells. CPO is highly expressed in intestinal epithelial cells in both zebrafish and human. These results suggest that CPO cleaves acidic amino acids from dietary proteins and peptides, thus complementing the actions of well known digestive carboxypeptidases CPA and CPB.

An overview of enzymatic reagents for the removal of affinity tags

Although they are often exploited to facilitate the expression and purification of recombinant proteins, every affinity tag, whether large or small, has the potential to interfere with the structure and function of its fusion partner. For this reason, reliable methods for removing affinity tags are needed. Only enzymes have the requisite specificity to be generally useful reagents for this purpose. In this review, the advantages and disadvantages of some commonly used endo- and exoproteases are discussed in light of the latest information.