Peptide inhibitors of angiotensin-I converting enzyme based on angiotensin (1-7) with selectivity for the C-terminal domain.

The renin-angiotensin system (RAS) is a key regulator of human arterial pressure. Several of its effects are modulated by angiotensin II, an octapeptide originating from the action of angiotensin-I converting enzyme (ACE) on the decapeptide angiotensin-I. ACE possess two active sites (nACE and cACE) that have their own kinetic and substrate specificities. ACE inhibitors are widely used as the first-line treatment for hypertension and other heart-related diseases, but because they inactivate both ACE domains, their use is associated with serious side effects. Thus, the search for domain-specific ACE inhibitors has been the focus of intense research. Angiotensin (1-7), a peptide that also belongs to the RAS, acts as a substrate of nACE and an inhibitor of cACE. We have synthetized 15 derivatives of Ang (1-7), sequentially removing the N-terminal amino acids and modifying peptides extremities, to find molecules with improved selectivity and inhibition properties. Ac-Ang (2-7)-NH2 is a good ACE inhibitor, resistant to cleavage and with improved cACE selectivity. Molecular dynamics simulations provided a model for this peptide's selectivity, due to Val3 and Tyr4 interactions with ACE subsites. Val3 has an important interaction with the S3 subsite, since its removal greatly reduced peptide-enzyme interactions. Taken together, our findings support ongoing studies using insights from the binding of Ac-Ang (2-7)-NH2 to develop effective cACE inhibitors.

Overexpression of Plasmodium falciparum M1 Aminopeptidase Promotes an Increase in Intracellular Proteolysis and Modifies the Asexual Erythrocytic Cycle Development.

Plasmodium falciparum, the most virulent of the human malaria parasite, is responsible for high mortality rates worldwide. We studied the M1 alanyl-aminopeptidase of this protozoan (PfA-M1), which is involved in the final stages of hemoglobin cleavage, an essential process for parasite survival. Aiming to help in the rational development of drugs against this target, we developed a new strain of P. falciparum overexpressing PfA-M1 without the signal peptide (overPfA-M1). The overPfA-M1 parasites showed a 2.5-fold increase in proteolytic activity toward the fluorogenic substrate alanyl-7-amido-4-methylcoumarin, in relation to the wild-type group. Inhibition studies showed that overPfA-M1 presented a lower sensitivity against the metalloaminopeptidase inhibitor bestatin and to other recombinant PfA-M1 inhibitors, in comparison with the wild-type strain, indicating that PfA-M1 is a target for the in vitro antimalarial activity of these compounds. Moreover, overPfA-M1 parasites present a decreased in vitro growth, showing a reduced number of merozoites per schizont, and also a decrease in the iRBC area occupied by the parasite in trophozoite and schizont forms when compared to the controls. Interestingly, the transgenic parasite displays an increase in the aminopeptidase activity toward Met-, Ala-, Leu- and Arg-7-amido-4-methylcoumarin. We also investigated the potential role of calmodulin and cysteine proteases in PfA-M1 activity. Taken together, our data show that the overexpression of PfA-M1 in the parasite cytosol can be a suitable tool for the screening of antimalarials in specific high-throughput assays and may be used for the identification of intracellular molecular partners that modulate their activity in P. falciparum.

Cathepsin K inhibitors based on 2-amino-1,3,4-oxadiazole derivatives.

Two new series of hitherto unknown dipeptides, containing an electrophilic nitrile or a non-electrophilic 2-amino-1,3,4-oxadiazole moiety were synthesized and evaluated in vitro as Cathepsin K (Cat K) inhibitors. From 14 compounds obtained, the oxadiazole derivatives 10a, 10b, 10e, and 10g acted as enzymatic competitive inhibitors with Ki values between 2.13 and 7.33 µM. Molecular docking calculations were carried out and demonstrated that all inhibitors performed hydrogen bonds with residues from the enzyme active site, such as Asn18. The best inhibitors (10a, 10b, 10g) could also perform these bonds with Cys25, and 10a showed the most stabilizing interaction energy (-134.36 kcal mol-1) with the active cavity. For the first time, derivatives based in 2-amino-1,3,4-oxadiazole scaffolds were evaluated, and the results suggested that this core displays a remarkable potential as a building block for Cat K inhibitors.

Sugarcane cystatins: From discovery to biotechnological applications.

Phytocystatins are tight-binding cysteine protease inhibitors produced by plants. The first phytocystatin described was isolated from Oryza sativa and, since then, cystatins from several plant species were reported, including from sugarcane. Sugarcane cystatins were unraveled in Sugarcane EST project database, after sequencing of cDNA libraries from various sugarcane tissues at different developmental stages and six sugarcane cystatins were cloned, expressed and characterized (CaneCPI-1 to CaneCPI-6). These recombinant proteins were produced in different expression systems and inhibited several cysteine proteases, including human cathepsins B and L, which can be involved in pathologies, such as cancer. In this review, we summarize a comprehensive history of all sugarcane cystatins, presenting an updated phylogenetic analysis; chromosomal localization, and genomic organization. We also present protein docking of CaneCPI-5 in the active site of human cathepsin B, insights about canecystatins structures; recombinant expression in different systems, comparison of their inhibitory activities against human cysteine cathepsins B, K, L, S, V, falcipains from Plasmodium falciparum and a cathepsin L-like from the sugarcane weevil Sphenophorus levis; and enlighten their potential and current applications in agriculture and health.

Gene expression studies and molecular characterization of a cathepsin L-like from the Asian citrus psyllid Diaphorina citri, vector of Huanglongbing.

Huanglongbing (HLB) is a devastating citrus disease associated with Candidatus Liberibacter asiaticus (CLas) and is transmitted by the psyllid Diaphorina citri Kuwayama. Diaphorina citri belongs to Hemiptera order, which has cysteine peptidases as the most abundant proteolytic enzymes present in digestive tract. As cysteine peptidases are involved in different insect development processes, this class of enzymes has acquired biotechnological importance. In this context, we identified a cathepsin L-like (DCcathL1) from the Diaphorina citri transcriptome database and expressed the enzyme in E. coli. Quantitative real-time RT-PCR was conducted to determine DCcathL1 gene expression in different parts and developmental phases of the insect. We observed that DCcathL1 expression in the gut was 2.59 and 2.87-fold higher than in the head and carcass, respectively. Furthermore, DCcathL1 expression was greater in eggs than in nymphs and adults, suggesting a putative role of the enzyme in the embryonic development. In addition, enzymatic inhibitory activity using four recombinant Citrus cystatins were performed. Among them, CsinCPI-2 was the strongest DCcathL1 inhibitor with a Ki value of 0.005 nM. Our results may contribute in the development of strategies for D. citri control, such as silencing the DCcathL1 gene and the use of transgenic plants that overexpress peptidase inhibitors.

Evaluación de la proteólisis en células aisladas vivas de Plasmodium falciparum aisladas durante los estadios asexuales sanguíneos / Proteolysis assessment in isolated Plasmodium falciparum living cells at the asexual blood stages

It has been demonstrated that proteases play crucial roles in Plasmodium falciparum infection and therefore have been considered as targets for the development of new therapeutic drugs. The aim of this study was to describe the specific proteolytic activity profile in all blood stages of P. falciparum isolated parasites in order to explore new antimalarial options. For this purpose, we used the fluorogenic substrate Z-Phe-Arg-MCA (Z: carbobenzoxy, MCA: 7-amino-4-methyl coumarine) and classic inhibitors for the different classes of proteolytic enzymes, such as phenylmethylsulfonyl fluoride (PMSF), 1.10-phenantroline, pepstatin A and E64 to study the inhibition profiles. As expected, due to the high metabolic activity in mature stages, the substrate was mostly degraded in the trophozoite and schizont, with specific activities ~ 20 times higher than in early stages (merozoite/rings). The major actors in substrate hydrolysis were cysteine proteases, as confirmed by the complete hydrolysis inhibition with E64 addition. Proteolytic activity was also inhibited in the presence of PMSF in all but the schizont stage. However, PMSF inhibition was the result of unspecific interaction with cysteine proteases as demonstrated by reversion of inhibition by dithiotreitol (DTT), indicating that serine protease activity is very low or null. To our knowledge, this is the first report aiming to describe the proteolytic profile of P. falciparum isolated parasites at all the erythrocytic cycle stages. The results and protocol described herein can be useful in the elucidation of stage specific action of proteolysis-inhibiting drugs and aid in the development of antimalarial compounds with protease inhibitory activity(AU)

e ha demostrado que las proteasas desempeñan funciones vitales en la infección por Plasmodium falciparum, y por lo tanto se consideran dianas en la elaboración de nuevos medicamentos terapéuticos. El objetivo del estudio era describir el perfil de actividad proteolítica específica de todas las etapas sanguíneas de parásitos aislados de P. falciparum con vistas a explorar nuevas opciones antimaláricas. Con ese propósito, utilizamos el sustrato fluorogénico Z-Phe-Arg-AMC (Z: carbobenzoxi, AMC: 7-amino-4-metilcumarina) e inhibidores clásicos para las diferentes clases de enzimas proteolíticas, tales como el fluoruro de fenilmetilsulfonilo (PMSF), 1,10-fenantrolina, pepstatina A y E64 para estudiar los perfiles de inhibición. Como se esperaba, debido a la elevada actividad metabólica de las etapas de madurez, el sustrato fue degradado mayormente en el trofozoíto y el esquizonte, con actividad específica ~ 20 veces superior a la de las etapas tempranas (merozoíto/ anillos). Los principales actores en la hidrólisis del sustrato fueron las cisteínas proteasas, lo que fue confirmado por la inhibición completa de la hidrólisis con la adición de E64. La actividad proteolítica también fue inhibida en presencia de PMSF en todas las etapas excepto el esquizonte. Sin embargo, la inhibición del PMSF fue resultado de una interacción inespecífica con las cisteínas proteasas, según lo demuestra la reversión de la inhibición con el ditiotreitol (DTT), lo que indica que la actividad de la serina proteasa es muy baja o inexistente. Que sepamos, este es el primer informe dirigido a describir el perfil proteolítico de parásitos aislados de P. falciparum en todas las etapas del ciclo eritrocítico. Los resultados y el protocolo que aquí se describen pueden ser útiles para dilucidar la acción específica de los medicamentos inhibidores de proteólisis en cada etapa, así como contribuir al desarrollo de compuestos antimaláricos con actividad inhibidora de la proteasa(AU)

Potent and selective inhibitors for M32 metallocarboxypeptidases identified from high-throughput screening of anti-kinetoplastid chemical boxes.

Enzymes of the M32 family are Zn-dependent metallocarboxypeptidases (MCPs) widely distributed among prokaryotic organisms and just a few eukaryotes including Trypanosoma brucei and Trypanosoma cruzi, the causative agents of sleeping sickness and Chagas disease, respectively. These enzymes are absent in humans and several functions have been proposed for trypanosomatid M32 MCPs. However, no synthetic inhibitors have been reported so far for these enzymes. Here, we present the identification of a set of inhibitors for TcMCP-1 and TbMCP-1 (two trypanosomatid M32 enzymes sharing 71% protein sequence identity) from the GlaxoSmithKline HAT and CHAGAS chemical boxes; two collections grouping 404 compounds with high antiparasitic potency, drug-likeness, structural diversity and scientific novelty. For this purpose, we adapted continuous fluorescent enzymatic assays to a medium-throughput format and carried out the screening of both collections, followed by the construction of dose-response curves for the most promising hits. As a result, 30 micromolar-range inhibitors were discovered for one or both enzymes. The best hit, TCMDC-143620, showed sub-micromolar affinity for TcMCP-1, inhibited TbMCP-1 in the low micromolar range and was inactive against angiotensin I-converting enzyme (ACE), a potential mammalian off-target structurally related to M32 MCPs. This is the first inhibitor reported for this family of MCPs and considering its potency and specificity, TCMDC-143620 seems to be a promissory starting point to develop more specific and potent chemical tools targeting M32 MCPs from trypanosomatid parasites.

Malaria infection promotes a selective expression of kinin receptors in murine liver.

BACKGROUND: Malaria represents a worldwide medical emergency affecting mainly poor areas. Plasmodium parasites during blood stages can release kinins to the extracellular space after internalization of host kininogen inside erythrocytes and these released peptides could represent an important mechanism in liver pathophysiology by activation of calcium signaling pathway in endothelial cells of vertebrate host. Receptors (B1 and B2) activated by kinins peptides are important elements for the control of haemodynamics in liver and its physiology. The aim of this study was to identify changes in the liver host responses (i.e. kinin receptors expression and localization) and the effect of ACE inhibition during malaria infection using a murine model. METHODS: Balb/C mice infected by Plasmodium chabaudi were treated with captopril, an angiotensin I-converting enzyme (ACE) inhibitor, used alone or in association with the anti-malarial chloroquine in order to study the effect of ACE inhibition on mice survival and the activation of liver responses involving B1R and B2R signaling pathways. The kinin receptors (B1R and B2R) expression and localization was analysed in liver by western blotting and immunolocalization in different conditions. RESULTS: It was verified that captopril treatment caused host death during the peak of malaria infection (parasitaemia about 45%). B1R expression was stimulated in endothelial cells of sinusoids and other blood vessels of mice liver infected by P. chabaudi. At the same time, it was also demonstrated that B1R knockout mice infected presented a significant reduction of survival. However, the infection did not alter the B2R levels and localization in liver blood vessels. CONCLUSIONS: Thus, it was observed through in vivo studies that the vasodilation induced by plasma ACE inhibition increases mice mortality during P. chabaudi infection. Besides, it was also seen that the anti-malarial chloroquine causes changes in B1R expression in liver, even after days of parasite clearance. The differential expression of B1R and B2R in liver during malaria infection may have an important role in the disease pathophysiology and represents an issue for clinical treatments.

Leishmanicidal and Immunomodulatory Activities of the Palladacycle Complex DPPE 1.1, a Potential Candidate for Treatment of Cutaneous Leishmaniasis.

The present study focused on the activity of the palladacycle complex DPPE 1.1 on Leishmania (Leishmania) amazonensis. Promastigotes of L. (L.) amazonensis were destroyed in vitro by nanomolar concentrations of DPPE 1.1, whereas intracellular amastigotes were killed at drug concentrations fivefold less toxic than those harmful to macrophages. L. (L.) amazonensis-infected BALB/c mice were treated by intralesional injection of DPPE 1.1. Animals treated with 3.5 and 7.0 mg/kg of DPPE 1.1 showed a significant decrease of foot lesion sizes and a parasite load reduction of 93 and 99%, respectively, when compared to untreated controls. Furthermore, DPPE 1.1 was non-toxic to treated animals. The cathepsin B activity of L. (L.) amazonensis amastigotes was inhibited by DPPE 1.1 as demonstrated spectrofluorometrically by use of a specific fluorogenic substrate. Analysis of T-cells populations in mice treated with DPPE 1.1 and untreated controls was performed by fluorescence-activated cell sorter (FACS). IFN-γ was measured in supernatants of lymphocytes from popliteal and inguinal lymph nodes isolated from treated and untreated mice and stimulated with L. (L.) amazonensis amastigotes extract and active TGF-ß was evaluated in supernatants of foot lesions; both dosages were carried out by means of a double-sandwich ELISA assay. A significant increase of TCD4+ and TCD8+ lymphocytes and IFN-γ secretion was displayed in mice treated with DPPE 1.1 compared to untreated animals, whereas a significant reduction of active TGF-ß was observed in treated mice. These findings open perspectives for further investment in DPPE 1.1 as an alternative option for the chemotherapy of cutaneous leishmaniasis.

Inhibition of Plasmodium falciparum cysteine proteases by the sugarcane cystatin CaneCPI-4.

Malaria is a disease caused by Plasmodium parasites that affects hundreds of millions of people. Plasmodium proteases are involved in invasion, erythrocyte egress and degradation of host proteins. Falcipains are well-studied cysteine peptidases located in P. falciparum food vacuoles that participate in hemoglobin degradation. Cystatins are natural cysteine protease inhibitors that are implicated in a wide range of regulatory processes. Here, we report that a cystatin from sugarcane, CaneCPI-4, is selectively internalized into P. falciparum infected erythrocytes and is not processed by the parasite proteolytic machinery. Furthermore, we demonstrated the inhibition of P. falciparum cysteine proteases by CaneCPI-4, suggesting that it can exert inhibitory functions inside the parasites. The inhibition of the proteolytic activity of parasite cells is specific to this cystatin, as the addition of an anti-CaneCPI-4 antibody completely abolished the inhibition. We extended the studies to recombinant falcipain-2 and falcipain-3 and demonstrated that CaneCPI-4 strongly inhibits these enzymes, with IC50 values of 12nM and 42nM, respectively. We also demonstrated that CaneCPI-4 decreased the hemozoin formation in the parasites, affecting the parasitemia. Taken together, this study identified a natural molecule as a potential antimalarial that specifically targets falcipains and also contributes to a better understanding of macromolecule acquisition by Plasmodium falciparum infected RBCs.

Substrate specificity profiling of M32 metallocarboxypeptidases from Trypanosoma cruzi and Trypanosoma brucei.

Metallocarboxypeptidases (MCPs) of the M32 family, while broadly distributed among prokaryotic organisms, have so far been only found in a few eukaryotes including trypanosomatids. Among these organisms are human and animal pathogens of medical relevance such as Trypanosoma brucei and Trypanosoma cruzi, the respective causative agents of sleeping sickness and Chagas disease. The M32 MCP orthologues found in these parasites share 72% protein sequence identity. They also present a cytosolic localization, a similar pattern of expression and a marked preference for Arg/Lys residues at P1'. To further explore MCPs substrate specificity beyond the S1' subsite, we employed four positional scanning synthetic combinatorial libraries (PS-SC) of fluorescence resonance energy transfer (FRET) peptides. Our results indicated that the T. brucei enzyme has a restricted selectivity for Phe in P1 position compared to T. cruzi MCP-1, which presented a wider range of substrate acceptance. The S2, S3 and S4 subsites, on the other hand, could accommodate a broad range of residues. On the basis of these results, we synthesized for each enzyme a series of FRET substrates which contained the most favourable residues in every position. In particular, for both MCPs acting on FRET pentapeptide substrates, catalytic efficiencies were ∼100 times higher compared with previously described chromogenic substrates. In fact, the fluorogenic peptide Abz-LLKFK(Dnp)-OH (Abz = ortho-aminobenzoic acid; Dnp = 2, 4-dinitrophenyl) described here can be used to monitor accurately TbMCP-1 activity in parasite cell-free extracts. These results provide valuable insights to develop selective substrates and inhibitors, to further understand the mechanisms and functions of M32 MCPs.

KBE009: An antimalarial bestatin-like inhibitor of the Plasmodium falciparum M1 aminopeptidase discovered in an Ugi multicomponent reaction-derived peptidomimetic library.

Malaria is a global human parasitic disease mainly caused by the protozoon Plasmodium falciparum. Increased parasite resistance to current drugs determines the relevance of finding new treatments against new targets. A novel target is the M1 alanyl-aminopeptidase from P. falciparum (PfA-M1), which is essential for parasite development in human erythrocytes and is inhibited by the pseudo-peptide bestatin. In this work, we used a combinatorial multicomponent approach to produce a library of peptidomimetics and screened it for the inhibition of recombinant PfA-M1 (rPfA-M1) and the in vitro growth of P. falciparum erythrocytic stages (3D7 and FcB1 strains). Dose-response studies with selected compounds allowed identifying the bestatin-based peptidomimetic KBE009 as a submicromolar rPfA-M1 inhibitor (Ki=0.4µM) and an in vitro antimalarial compound as potent as bestatin (IC50=18µM; without promoting erythrocyte lysis). At therapeutic-relevant concentrations, KBE009 is selective for rPfA-M1 over porcine APN (a model of these enzymes from mammals), and is not cytotoxic against HUVEC cells. Docking simulations indicate that this compound binds PfA-M1 without Zn2+ coordination, establishing mainly hydrophobic interactions and showing a remarkable shape complementarity with the active site of the enzyme. Moreover, KBE009 inhibits the M1-type aminopeptidase activity (Ala-7-amido-4-methylcoumarin substrate) in isolated live parasites with a potency similar to that of the antimalarial activity (IC50=82µM), strongly suggesting that the antimalarial effect is directly related to the inhibition of the endogenous PfA-M1. These results support the value of this multicomponent strategy to identify PfA-M1 inhibitors, and make KBE009 a promising hit for drug development against malaria.

High aminopeptidase A activity contributes to blood pressure control in ob/ob mice by AT2 receptor-dependent mechanism.

Obesity is assumed to be a major cause of human essential hypertension; however, the mechanisms responsible for weight-related increase in blood pressure (BP) are not fully understood. The prevalence of hypertension induced by obesity has grown over the years, and the role of the renin-angiotensin-aldosterone system (RAAS) in this process continues to be elucidated. In this scenario, the ob/ob mice are a genetic obesity model generally used for metabolic disorder studies. These mice are normotensive even though they present several metabolic conditions that predispose them to hypertension. Although the normotensive trait in these mice is associated with the poor activation of sympathetic nervous system by the lack of leptin, we demonstrated that ob/ob mice present massively increased aminopeptidase A (APA) activity in the circulation. APA enzyme metabolizes angiotensin (ANG) II into ANG III, a peptide associated with intrarenal angiotensin type 2 (AT2) receptor activation and induction of natriuresis. In these mice, we found increased ANG-III levels in the circulation, high AT2 receptor expression in the kidney, and enhanced natriuresis. AT2 receptor blocking and APA inhibition increased BP, suggesting the ANG III-AT2 receptor axis as a complementary BP control mechanism. Circulating APA activity was significantly reduced by weight loss independently of leptin, indicating the role of fat tissue in APA production. Therefore, in this study we provide new data supporting the role of APA in BP control in ob/ob mouse strain. These findings improve our comprehension about obesity-related hypertension and suggest new tools for its treatment.NEW & NOTEWORTHY In this study, we reported an increased angiotensin III generation in the circulation of ob/ob mice caused by a high aminopeptidase A activity. These findings are associated with an increased natriuresis found in these mice and support the role of renin-angiotensin-aldosterone system as additional mechanism regulating blood pressure in this genetic obese strain.

The effect of structural motifs on the ectodomain shedding of human angiotensin-converting enzyme.

Somatic angiotensin converting enzyme (sACE) is comprised of two homologous domains (N and C domains), whereas the smaller germinal isoform (tACE) is identical to the C domain. Both isozymes share an identical stalk, transmembrane and cytoplasmic domain, and undergo ectodomain shedding by an as yet unknown protease. Here we present evidence for the role of regions distal and proximal to the cleavage site in human ACE shedding. First, because of intrinsic differences between the N and C domains, discrete secondary structures (α-helix 7 and 8) on the surface of tACE were replaced with their N domain counterparts. Surprisingly, neither α-helix 7 nor α-helix 8 proved to be an absolute requirement for shedding. In the proximal ectodomain of tACE residues H610-L614 were mutated to alanines and this resulted in a decrease in ACE shedding. An N-terminal extension of this mutation caused a reduction in cellular ACE activity. More importantly, it affected the processing of the protein to the membrane, resulting in expression of an underglycosylated form of ACE. When E608-H614 was mutated to the homologous region of the N domain, processing was normal and shedding only moderately decreased suggesting that this region is more crucial for the processing of ACE than it is for regulating shedding. Finally, to determine whether glycosylation of the asparagine proximal to the Pro1199-Leu polymorphism in sACE affected shedding, the equivalent P623L mutation in tACE was investigated. The P623L tACE mutant showed an increase in shedding and MALDI MS analysis of a tryptic digest indicated that N620WT was glycosylated. The absence of an N-linked glycan at N620, resulted in an even greater increase in shedding. Thus, the conformational flexibility that the leucine confers to the stalk, is increased by the lack of glycosylation reducing access of the sheddase to the cleavage site.

Paramagnetic bradykinin analogues as substrates for angiotensin I-converting enzyme: Pharmacological and conformation studies.

This study uses EPR, CD, and fluorescence spectroscopy to examine the structure of bradykinin (BK) analogues attaching the paramagnetic amino acid-type Toac (2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid) at positions 0, 3, 7, and 9. The data were correlated with the potencies in muscle contractile experiments and the substrate properties towards the angiotensin I-converting enzyme (ACE). A study of the biological activities in guinea pig ileum and rat uterus indicated that only Toac0-BK partially maintained its native biological potency among the tested peptides. This and its counterpart, Toac3-BK, maintained the ability to act as ACE substrates. These results indicate that peptides bearing Toac probe far from the ACE cleavage sites were more susceptible to hydrolysis by ACE. The results also emphasize the existence of a finer control for BK-receptor interaction than for BK binding at the catalytic site of this metallodipetidase. The kinetic kcat/Km values decreased from 202.7 to 38.9µM-1min-1 for BK and Toac3-BK, respectively. EPR, CD, and fluorescence experiments reveal a direct relationship between the structure and activity of these paramagnetic peptides. In contrast to the turn-folded structures of the Toac-internally labeled peptides, more extended conformations were displayed by N- or C-terminally Toac-labeled analogues. Lastly, this work supports the feasibility of monitoring the progress of the ACE-hydrolytic process of Toac-attached peptides by examining time-dependent EPR spectral variations.

TLR4-mediated immunomodulatory properties of the bacterial metalloprotease arazyme in preclinical tumor models.

Despite the recent approval of new agents for metastatic melanoma, its treatment remains challenging. Moreover, few available immunotherapies induce a strong cellular immune response, and selection of the correct immunoadjuvant is crucial for overcoming this obstacle. Here, we studied the immunomodulatory properties of arazyme, a bacterial metalloprotease, which was previously shown to control metastasis in a murine melanoma B16F10-Nex2 model. The antitumor activity of arazyme was independent of its proteolytic activity, since heat-inactivated protease showed comparable properties to the active enzyme; however, the effect was dependent on an intact immune system, as antitumor properties were lost in immunodeficient mice. The protective response was IFNγ-dependent, and CD8(+) T lymphocytes were the main effector antitumor population, although B and CD4(+) T lymphocytes were also induced. Macrophages and dendritic cells were involved in the induction of the antitumor response, as arazyme activation of these cells increased both the expression of surface activation markers and proinflammatory cytokine secretion through TLR4-MyD88-TRIF-dependent, but also MAPK-dependent pathways. Arazyme was also effective in the murine breast adenocarcinoma 4T1 model, reducing primary and metastatic tumor development, and prolonging survival. To our knowledge, this is the first report of a bacterial metalloprotease interaction with TLR4 and subsequent receptor activation that promotes a proinflammatory and tumor protective response. Our results show that arazyme has immunomodulatory properties, and could be a promising novel alternative for metastatic melanoma treatment.

Expression and inactivation of osteopontin-degrading PHEX enzyme in squamous cell carcinoma.

Proteolytic enzymes mediate the activation or inactivation of many physiologic and pathologic processes. The PHEX gene (Phosphate-regulating gene with homologies to endopeptidase on the X chromosome) encodes a metallopeptidase, which is mutated in patients with a prevalent form (1:20,000) of inherited rickets-X-linked hypophosphatemia (XLH). XLH shows growth retardation, hypophosphatemia, osteomalacia, and defective renal phosphate reabsorption and metabolism of vitamin D. Most PHEX studies have focused on bone, and recently we identified osteopontin (OPN) as the first protein substrate for PHEX, demonstrating in the murine model of XLH (Hyp mice) an increase in OPN that contributes to the osteomalacia. Besides its role in bone mineralization, OPN is expressed in many tissues, and therein has different functions. In tumor biology, OPN is known to be associated with metastasis. Here, we extend our PHEX-OPN studies to investigate PHEX expression in a squamous cell carcinoma (SCC) cell line and its possible involvement in modulating OPN function. Real-time PCR showed PHEX-OPN co-expression in SCC cells, with sequencing of the 22 exons showing no mutation of the PHEX gene. Although recombinant PHEX hydrolyze SCC-OPN fragments, unlike in bone cells, SCC-PHEX protein was not predominantly at the plasma membrane. Enzymatic activity assays, FACs and immunoblotting analyses demonstrated that membrane PHEX is degraded by cysteine proteases and the decreased PHEX activity could contribute to inappropriate OPN regulation. These results highlight for the first time PHEX in tumor biology.

Hypervalent organotellurium compounds as inhibitors of P. falciparum calcium-dependent cysteine proteases.

Hypervalent organotellurium compounds (organotelluranes) have shown several promising applications, including their use as potent and selective cysteine protease inhibitors and antiprotozoal agents. Here, we report the antimalarial activities of three organotellurane derivatives (RF05, RF07 and RF19) in two Plasmodium falciparum strains (CQS 3D7 and CQR W2), which demonstrated significant decreases in parasitemia in vitro. The inhibition of intracellular P. falciparum proteases by RF05, RF07 and RF19 was determined and the IC50 values were 3.7±1.0µM, 1.1±0.2µM and 0.2±0.01µM, respectively. Using an assay performed in the presence of the ER Ca(2+)-ATPase inhibitor we showed that the main enzymatic targets were cysteine proteases stimulated by calcium (calpains). None of the compounds tested caused haemolysis or a significant decrease in endothelial cell viability in the concentration range used for the inhibition assay. Taken together, the results suggest promising compounds for the development of antimalarial drugs.

Calmidazolium evokes high calcium fluctuations in Plasmodium falciparum.

Calcium and calmodulin (CaM) are important players in eukaryote cell signaling. In the present study, by using a knockin approach, we demonstrated the expression and localization of CaM in all erythrocytic stages of Plasmodium falciparum. Under extracellular Ca(2+)-free conditions, calmidazolium (CZ), a potent CaM inhibitor, promoted a transient cytosolic calcium ([Ca(2+)]cyt) increase in isolated trophozoites, indicating that CZ mobilizes intracellular sources of calcium. In the same extracellular Ca(2+)-free conditions, the [Ca(2+)]cyt rise elicited by CZ treatment was ~3.5 fold higher when the endoplasmic reticulum (ER) calcium store was previously depleted ruling out the mobilization of calcium from the ER by CZ. The effects of the Ca(2+)/H(+) ionophore ionomycin (ION) and the Na(+)/H(+) ionophore monensin (MON) suggest that the [Ca(2+)]cyt-increasing effect of CZ is driven by the removal of Ca(2+) from at least one Ca(2+)-CaM-related (CaMR) protein as well as by the mobilization of Ca(2+) from intracellular acidic calcium stores. Moreover, we showed that the mitochondrion participates in the sequestration of the cytosolic Ca(2+) elicited by CZ. Finally, the modulation of membrane Ca(2+) channels by CZ and thapsigargin (THG) was demonstrated. The opened channels were blocked by the unspecific calcium channel blocker Co(2+) but not by 2-APB (capacitative calcium entry inhibitor) or nifedipine (L-type Ca(2+) channel inhibitor). Taken together, the results suggested that one CaMR protein is an important modulator of calcium signaling and homeostasis during the Plasmodium intraerythrocytic cell cycle, working as a relevant intracellular Ca(2+) reservoir in the parasite.

Conformational Properties of Seven Toac-Labeled Angiotensin I Analogues Correlate with Their Muscle Contraction Activity and Their Ability to Act as ACE Substrates.

Conformational properties of the angiotensin II precursor, angiotensin I (AngI) and analogues containing the paramagnetic amino acid TOAC (2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid) at positions 0, 1, 3, 5, 8, 9, and 10, were examined by EPR, CD, and fluorescence. The conformational data were correlated to their activity in muscle contraction experiments and to their properties as substrates of the angiotensin I-converting enzyme (ACE). Biological activity studies indicated that TOAC0-AngI and TOAC1-AngI maintained partial potency in guinea pig ileum and rat uterus. Kinetic parameters revealed that only derivatives labeled closer to the N-terminus (positions 0, 1, 3, and 5) were hydrolyzed by ACE, indicating that peptides bearing the TOAC moiety far from the ACE cleavage site (Phe8-His9 peptide bond) were susceptible to hydrolysis, albeit less effectively than the parent compound. CD spectra indicated that AngI exhibited a flexible structure resulting from equilibrium between different conformers. While the conformation of N-terminally-labeled derivatives was similar to that of the native peptide, a greater propensity to acquire folded structures was observed for internally-labeled, as well as C-terminally labeled, analogues. These structures were stabilized in secondary structure-inducing agent, TFE. Different analogues gave rise to different ß-turns. EPR spectra in aqueous solution also distinguished between N-terminally, internally-, and C-terminally labeled peptides, yielding narrower lines, indicative of greater mobility for the former. Interestingly, the spectra of peptides labeled at, or close, to the C-terminus, showed that the motion in this part of the peptides was intermediate between that of N-terminally and internally-labeled peptides, in agreement with the suggestion of turn formation provided by the CD spectra. Quenching of the Tyr4 fluorescence by the differently positioned TOAC residues corroborated the data obtained by the other spectroscopic techniques. Lastly, we demonstrated the feasibility of monitoring the progress of ACE-catalyzed hydrolysis of TOAC-labeled peptides by following time-dependent changes in their EPR spectra.