Peptidase specificity characterization of C- and N-terminal catalytic sites of angiotensin I-converting enzyme

Pharmacoinformatics studies of coenzyme Q10 and potassium polyacrylate on angiotensin-converting enzyme associated with hypertension

Coenzyme Q10's (CoQ10) favorable impact on cardiovascular diseases risk factors like hypertension and atherosclerosis is linked to the antioxidant action of CoQ10 in these conditions. This study showed the possible effects of CoQ10, potassium polyacrylate (PCK), and valsartan, a reference drug, on the angiotensin-converting enzyme (ACE), a crucial component of the renin-angiotensin system. The Glide tool on Maestro 11.1 was used to calculate the respective binding affinity and binding energy of these compounds towards ACE. The Schrödinger suite was used to run molecular dynamic simulations for 100 ns. The pkCSM tool was used to forecast the pharmacokinetic characteristics and toxicological effects. The SwissADME server was used to estimate the drug-like properties of these compounds. Based on their corresponding scoring values and the negative values of the binding free energies, molecular docking analysis of CoQ10 and PCK revealed that both exhibited favorable binding affinities towards the ACE, with CoQ10 having the highest binding scores. The results showed that both CoQ10 and PCK and the reference drug, valsartan, have some amino acids in common (at the pocket site of ACE) as the key residues for binding to ACE. Both CoQ10 and PCK demonstrated drug-like qualities and were not harmful, according to the predicted pharmacokinetics and toxicology studies. The results of this study suggest that because of its inhibitory interactions with ACE, CoQ10 in particular could be useful in regulating and reducing hypertension.Communicated by Ramaswamy H. Sarma.

The role of the renin-angiotensin system (RAS) in salinity adaptation in Pacific white shrimp (Litopenaeus vannamei)

The renin-angiotensin system (RAS) is a hormonal system that plays an important role in the regulation of blood pressure and cardiovascular homeostasis in mammals. In fishes, the RAS pathway participates in osmoregulation and salinity adaptation. However, the role of the RAS pathway in invertebrates, particularly in crustaceans, remains unknown. In this study, four key genes of the RAS pathway (LV-ACE, LV-APN, LV-AT1R, and LV-RR) were cloned, characterized, and their expression levels were detected in the eyestalk, hepatopancreas, and muscle of Litopenaeus vannamei during long-term and short-term low salinity stress. The results showed that LV-ACE, LV-APN, LV-AT1R, and LV-RR encode 666, 936, 175, and 323 amino acids, respectively. Low salinity stress downregulated the expression levels of LV-ACE, LV-APN, LV-AT1R, and LV-RR in L. vannamei, indicating that the RAS pathway was suppressed under low salinity. Moreover, these genes play important roles in the regulation of drinking rate, controlling urine output, blood glucose, and blood pressure, indicating that their downregulation probably affected the homeostasis of shrimps. These findings provide novel insights into the mechanism of salinity adaptation in L. vannamei.

Probing the Conformational States of Thimet Oligopeptidase in Solution

Thimet oligopeptidase (TOP) is a metallopeptidase involved in the metabolism of oligopeptides inside and outside cells of various tissues. It has been proposed that substrate or inhibitor binding in the TOP active site induces a large hinge-bending movement leading to a closed structure, in which the bound ligand is enclosed. The main goal of the present work was to study this conformational change, and fluorescence techniques were used. Four active TOP mutants were created, each equipped with a single-Trp residue (fluorescence donor) and a p-nitro-phenylalanine (pNF) residue as fluorescence acceptor at opposite sides of the active site. pNF was biosynthetically incorporated with high efficiency using the amber codon suppression technology. Inhibitor binding induced shorter Donor-Acceptor (D-A) distances in all mutants, supporting the view that a hinge-like movement is operative in TOP. The activity of TOP is known to be dependent on the ionic strength of the assay buffer and D-A distances were measured at different ionic strengths. Interestingly, a correlation between the D-A distance and the catalytic activity of TOP was observed: the highest activities corresponded to the shortest D-A distances. In this study for the first time the hinge-bending motion of a metallopeptidase in solution could be studied, yielding insight about the position of the equilibrium between the open and closed conformation. This information will contribute to a more detailed understanding of the mode of action of these enzymes, including therapeutic targets like neurolysin and angiotensin-converting enzyme 2 (ACE2).

Measurement of serum ACE status may potentially improve the diagnosis of SARS-CoV-2 infection

The severity of SARS-CoV-2 infection is associated with underlying cardiovascular or pulmonary pathological conditions. The fatality rate of this typical pneumonia has superseded the two previous coronavirus epidemics combined. Thus far, comprehensive diagnosis of SARS-CoV-2 remains essential for effective screening, detection, and disease monitoring. This allows employment of different life-saving interventions to lower the spread and mortality, whilst the development of labelled therapeutics is underway. In this perspective, the measurement of Angiotensin-converting enzyme (ACE) status is perceived as a potential prognostic biomarker for SARS-CoV-2 patients. This notion is based on the observation that SARS-CoV-2 infection via attachment to Angiotensin-converting enzyme-2 (ACE2) receptor, downregulates ACE2 expression. Thus leading to the inability to efficiently counter-regulate the damaging effects of its homolog; ACE. The perspective is further strengthened by the recommendations of therapeutics that attenuate the conversion of Angiotensin I to a vasoconstrictor; Angiotensin II as an effective treatment of SARS-CoV-2 infection. In addition, other off-labelled used drugs target the latter; restoration of multiple organ failure and or cytokine storm inhibition. Therefore, this suggests that ACE may be strongly implicated in the pathogenesis of SARS-CoV-2.

Milk Fermentation by Lacticaseibacillus rhamnosus GG and Streptococcus thermophilus SY-102: Proteolytic Profile and ACE-Inhibitory Activity

Health benefits of probiotics and production of inhibitors of angiotensin converting enzyme (ACE) released during milk fermentation are well known. That is why in this investigation the proteolytic profile and ACE inhibitory capacity of peptide fractions from protein hydrolysis of milk during fermentation processes was analyzed. Milk fermentation was carried out inoculating 106 CFU of L. rhamnosus GG, S. thermophilus SY-102 and with both bacteria. The proteolytic profile was determined using: TNBS, SDS-PAGE and SEC-HPLC techniques. In vitro ACE inhibition capacity was measured. The pH of 4.5 was reached at 56 h when the milk was fermented with L. rhamnosus, at 12 h with S. thermophillus and at 41 h in the co-culture. Production of free amino groups corresponded with the profile of low molecular weight peptides observed by SDS-PAGE and SEC-HPLC. Co-culture fermentation showed both the highest concentration of low molecular weight peptides and the ACE inhibitory activity (>80%). Results indicated that the combination of lactic cultures could be useful in manufacture of fermented milk with an added value that goes beyond basic nutrition, such as the production of ACE-inhibitory peptides.

Hypotensive and Hepatoprotective Properties of the Polysaccharide-Stabilized Foaming Composition Containing Hydrolysate of Whey Proteins

Whey protein hydrolysates (WPHs) are one of the most promising sources of biofunctional peptides with such beneficial properties as antioxidant, antihypertensive, anti-inflammatory and others. WPHs also could be used as foaming agents for aerated products (e.g., milk shake type drinks). However, WPH alone has a bitter taste and foamed WPH should be stabilized by additional ingredients. Here, we present a composition including WPH and three polysaccharides-pumpkin pectin, sodium alginate and ι-carrageenan-used as foam stabilizers. Polysaccharide content was selected according to foaming, organoleptic antioxidant and angiotensin-I-converting enzyme inhibitory characteristics of the resulted composition. Further, the hypotensive, antioxidant and hepatoprotective properties of the composition were proved by in vivo tests performed in spontaneously hypertensive rats and Wistar rats with CCl₄-induced hepatic injury.

Design, synthesis, and evaluation of Bothrops venom serine protease peptidic inhibitors

Background:

In Central and South America, snakebite envenomation is mainly caused by Bothrops spp. snakes, whose venoms feature significant biochemical richness, including serine proteases. The available bothropic antivenoms are efficient in avoiding fatalities, but do not completely neutralize venom serine proteases, which are co-responsible for some disorders observed during envenomation.

Methods:

In order to search for tools to improve the antivenom’s, 6-mer peptides were designed based on a specific substrate for Bothrops jararaca venom serine proteases, and then synthesized, with the intention to selectively inhibit these enzymes.

Results:

Using batroxobin as a snake venom serine protease model, two structurally similar inhibitor peptides were identified. When tested on B. jararaca venom, one of the new inhibitors displayed a good potential to inhibit the activity of the venom serine proteases. These inhibitors do not affect human serine proteases as human factor Xa and thrombin, due to their selectivity.

Conclusion:

Our study identified two small peptides able to inhibit bothropic serine proteases, but not human ones, can be used as tools to enhance knowledge of the venom composition and function. Moreover, one promising peptide (pepC) was identified that can be explored in the search for improving Bothrops spp. envenomation treatment.

Whey Protein Hydrolysate and Pumpkin Pectin as Nutraceutical and Prebiotic Components in a Functional Mousse with Antihypertensive and Bifidogenic Properties

Systematical consumption of functional products has a significant positive effect on health and can reduce the risk of diseases. The aim of this study was to investigate the possibility of using whey protein hydrolysate (WPH) and pumpkin pectin as ingredients in a functional mousse, to evaluate the mousse’s antioxidant and hypotensive activities in vitro, and to evaluate the effect of the long-term intake of mousse samples on the progression of hypertension in spontaneously hypertensive rats (SHRs) and on the microbiome status in Wistar rats with antibiotic-induced dysbiosis. The experimental mousse’s in vitro antioxidant activity (oxygen radical absorbance capacity) increased by 1.2 times. The hypotensive (angiotensin-1-converting enzyme inhibitory) activity increased by 6 times in comparison with a commercial mousse. Moreover, the addition of pectin allowed the elimination of the bitter aftertaste of WPH. In vivo testing confirmed the hypotensive properties of the experimental mousse. The systolic blood pressure in SHRs decreased by 18 mmHg and diastolic blood pressure by 12 mmHg. The experimental mousse also showed a pronounced bifidogenic effect. The Bifidobacterium spp. population increased by 3.7 times in rats orally administered with the experimental mousse. The results of these studies confirm that WPH and pumpkin pectin are prospective ingredients for the development of functional mousses.

Interacting cogs in the machinery of the renin angiotensin system

Somatic angiotensin converting enzyme (sACE) is well-known for its role in blood pressure regulation and consequently, ACE inhibitors are widely prescribed for the treatment of hypertension. More than 60 years after the discovery of sACE, however, the molecular details of its substrate hydrolysis and inhibition are still poorly understood. Isothermal titration calorimetry, molecular dynamics simulations and fine epitope mapping suggest that substrate or inhibitor binding triggers a hinging motion between the two subdomains of each domain. Ligand binding to one domain further induces a conformational change in sACE to negatively affect the second domain's function and can also cause dimerization between sACE molecules. This has been linked to an increase in sACE expression via intracellular signalling. Inhibitor-induced dimerization could thus decrease the efficacy of hypertension treatment. At present, the only structural information available for sACE are crystal structures of the truncated domains in the closed conformation due to the presence of ligands. These structures do not provide any information regarding the open active site conformation prior to ligand binding, the relative orientation of the two domains in full-length sACE, or the dimerization interface. To guarantee effective therapeutic intervention, further research is required to investigate the hinging, negative cooperativity and dimerization of sACE. This review describes our current understanding of these interactions and proposes how recent advances in cryo-electron microscopy could enable structural elucidation of their mechanisms.

The Plethora of Angiotensin-Converting Enzyme-Processed Peptides in Mouse Plasma

Angiotensin-converting enzyme (ACE) converts angiotensin I into the potent vasoconstrictor angiotensin II, which regulates blood pressure. However, ACE activity is also essential for other physiological functions, presumably through processing of peptides unrelated to angiotensin. The goal of this study was to identify novel natural substrates and products of ACE through a series of mass-spectrometric experiments. This included comparing the ACE-treated and untreated plasma peptidomes of ACE-knockout (KO) mice, validation with select synthetic peptides, and a quantitative in vivo study of ACE substrates in mice with distinct genetic ACE backgrounds. In total, 244 natural peptides were identified ex vivo as possible substrates or products of ACE, demonstrating high promiscuity of the enzyme. ACE prefers to cleave substrates with Phe or Leu at the C-terminal P2' position and Gly in the P6 position. Pro in P1' and Iso in P1 are typical residues in peptides that ACE does not cleave. Several of the novel ACE substrates are known to have biological activities, including a fragment of complement C3, the spasmogenic C3f, which was processed by ACE ex vivo and in vitro. Analyses with N-domain-inactive (NKO) ACE allowed clarification of domain selectivity toward substrates. The in vivo ACE-substrate concentrations in WT, transgenic ACE-KO, NKO, and CKO mice correspond well with the in vitro observations in that higher levels of the ACE substrates were observed when the processing domain was knocked out. This study highlights the vast extent of ACE promiscuity and provides a valuable platform for further investigations of ACE functionality.

Molecular Basis for Multiple Omapatrilat Binding Sites within the ACE C-Domain: Implications for Drug Design

Omapatrilat was designed as a vasopeptidase inhibitor with dual activity against the zinc metallopeptidases angiotensin-1 converting enzyme (ACE) and neprilysin (NEP). ACE has two homologous catalytic domains (nACE and cACE), which exhibit different substrate specificities. Here, we report high-resolution crystal structures of omapatrilat in complex with nACE and cACE and show omapatrilat has subnanomolar affinity for both domains. The structures show nearly identical binding interactions for omapatrilat in each domain, explaining the lack of domain selectivity. The cACE complex structure revealed an omapatrilat dimer occupying the cavity beyond the S₂ subsite, and this dimer had low micromolar inhibition of nACE and cACE. These results highlight residues beyond the S₂ subsite that could be exploited for domain selective inhibition. In addition, it suggests the possibility of either domain specific allosteric inhibitors that bind exclusively to the nonprime cavity or the potential for targeting specific substrates rather than completely inhibiting the enzyme.

Aerobic exercise training differentially affects ACE C- and N-domain activities in humans: Interactions with ACE I/D polymorphism and association with vascular reactivity

Introduction:

Previous studies have linked angiotensin-converting enzyme (ACE) insertion (I)/deletion (D) polymorphism (II, ID and DD) to physical performance. Moreover, ACE has two catalytic domains: NH2 (N) and COOH (C) with distinct functions, and their activity has been found to be modulated by ACE polymorphism. The aim of the present study is to investigate the effects of the interaction between aerobic exercise training (AET) and ACE I/D polymorphism on ACE N- and C-domain activities and vascular reactivity in humans.

Materials and methods:

A total of 315 pre-selected healthy males were genotyped for II, ID and DD genotypes. Fifty completed the full AET (II, n = 12; ID, n = 25; and DD, n = 13), performed in three 90-minute sessions weekly, in the four-month exercise protocol. Pre- and post-training resting heart rate (HR), peak O₂ consumption (VO₂ peak), mean blood pressure (MBP), forearm vascular conduction (FVC), total circulating ACE and C- and N-domain activities were assessed. One-way ANOVA and two-way repeated-measures ANOVA were used.

Results:

In pre-training, all variables were similar among the three genotypes. In post-training, a similar increase in FVC (35%) was observed in the three genotypes. AET increased VO₂ peak similarly in II, ID and DD (49±2 vs. 57±1; 48±1 vs. 56±3; and 48±5 vs. 58±2 ml/kg/min, respectively). Moreover, there were no changes in HR and MBP. The DD genotype was also associated with greater ACE and C-domain activities at pre- and post-training when compared to II. AET decreased similarly the total ACE and C-domain activities in all genotypes, while increasing the N-domain activity in the II and DD genotypes. However, interestingly, the measurements of N-domain activity after training indicate a greater activity than the other genotypes. These results suggest that the vasodilation in response to AET may be associated with the decrease in total ACE and C-domain activities, regardless of genotype, and that the increase in N-domain activity is dependent on the DD genotype.

Conclusions:

AET differentially affects the ACE C- and N-domain activities, and the N-domain activity is dependent on ACE polymorphism.

D-Arg0-Bradykinin-Arg-Arg, a Latent Vasoactive Bradykinin B2 Receptor Agonist Metabolically Activated by Carboxypeptidases

We previously reported hypotensive and vasodilator effects from C-terminally extended bradykinin (BK) sequences that behave as B₂ receptor (B₂R) agonists activated by vascular or plasma peptidases. D-Arg⁰-BK-Arg-Arg (r-BK-RR) is a novel prodrug peptide hypothetically activated by two catalytic cycles of Arg-carboxypeptidases (CPs) to release the direct agonist D-Arg⁰-BK. N-terminally extending the BK sequence with D-Arg⁰ in the latter peptide was meant to block the second kinin inactivation pathway in importance, aminopeptidase P. The affinity of r-BK and r-BK-RR for recombinant B₂R was assessed using a [³H]BK binding displacement assay. Their pharmacology was evaluated in human isolated umbilical vein, a contractile bioassay for the B₂R, in a morphological assay involving the endocytosis of B₂R-green fusion protein (GFP) and in anesthetized rats instrumented to record hemodynamic responses to bolus intravenous injection of both peptides. r-BK exhibited an affinity equal to that of BK for the rat B₂R, while r-BK-RR was 61-fold less potent. In the vein and the B₂R-GFP internalization assay, r-BK was a direct agonist unaffected by the blockade of angiotensin converting enzyme (ACE) with enalaprilat, or Arg-CPs with Plummer’s inhibitor. However, the in vitro effects of r-BK-RR were reduced by these inhibitors, more so by enalaprilat. In anesthetized rats, r-BK and r-BK-RR were equipotent hypotensive agents and their effects were inhibited by icatibant (a B₂R antagonist). The hypotensive effects of r-BK were potentiated by enalaprilat, but not influenced by the Arg-CPs inhibitor, which is consistent with a minor role of Arg-CPs in the metabolism of r-BK. However, in rats pretreated with both enalaprilat and Plummer’s inhibitor, the hypotensive responses and the duration of the hypotensive episode to r-BK were significantly potentiated. The hypotensive responses to r-BK-RR were not affected by enalaprilat, but were reduced by pre-treatment with the Arg-CPs inhibitor alone or combined with enalaprilat. Therefore, in vivo, Arg-CPs activity is dominant over ACE to regenerate the B₂R agonist r-BK from r-BK-RR, a prodrug activator of the B₂R. A B₂R agonist activated only at the level of the microcirculation by resident peptidases could be developed as an intravenously infused drug for ischemic diseases.

Crystal structures of sampatrilat and sampatrilat-Asp in complex with human ACE - a molecular basis for domain selectivity

Angiotensin‐1‐converting enzyme (ACE) is a zinc metallopeptidase that consists of two homologous catalytic domains (known as nACE and cACE) with different substrate specificities. Based on kinetic studies it was previously reported that sampatrilat, a tight‐binding inhibitor of ACE, K_i = 13.8 nm and 171.9 nm for cACE and nACE respectively [Sharma et al., Journal of Chemical Information and Modeling (2016), 56, 2486–2494], was 12.4‐fold more selective for cACE. In addition, samAsp, in which an aspartate group replaces the sampatrilat lysine, was found to be a nonspecific and lower micromolar affinity inhibitor. Here, we report a detailed three‐dimensional structural analysis of sampatrilat and samAsp binding to ACE using high‐resolution crystal structures elucidated by X‐ray crystallography, which provides a molecular basis for differences in inhibitor affinity and selectivity for nACE and cACE. The structures show that the specificity of sampatrilat can be explained by increased hydrophobic interactions and a H‐bond from Glu403 of cACE with the lysine side chain of sampatrilat that are not observed in nACE. In addition, the structures clearly show a significantly greater number of hydrophilic and hydrophobic interactions with sampatrilat compared to samAsp in both cACE and nACE consistent with the difference in affinities. Our findings provide new experimental insights into ligand binding at the active site pockets that are important for the design of highly specific domain selective inhibitors of ACE.

Database

The atomic coordinates and structure factors for N‐ and C‐domains of ACE bound to sampatrilat and sampatrilat‐Asp complexes (6F9V, 6F9R, 6F9T and 6F9U respectively) have been deposited in the Protein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers University, New Brunswick, NJ (http://www.rcsb.org/).

Structure-function studies of BPP-BrachyNH2 and synthetic analogues thereof with Angiotensin I-Converting Enzyme

The vasoactive proline-rich oligopeptide termed BPP-BrachyNH₂ (H-WPPPKVSP-NH₂) induces in vitro inhibitory activity of angiotensin I-converting enzyme (ACE) in rat blood serum. In the present study, the removal of N-terminal tryptophan or C-terminal proline from BPP-BrachyNH₂ was investigated in order to predict which structural components are important or required for interaction with ACE. Furthermore, the toxicological profile was assessed by in silico prediction and in vitro MTT assay. Two BPP-BrachyNH₂ analogues (des-Trp¹-BPP-BrachyNH₂ and des-Pro⁸-BPP-BrachyNH₂) were synthesized, and in vitro and in silico ACE inhibitory activity and toxicological profile were assessed. The des-Trp¹-BPP-BrachyNH₂ and des-Pro⁸-BPP-BrachyNH₂ were respectively 3.2- and 29.5-fold less active than the BPP-BrachyNH₂-induced ACE inhibitory activity. Molecular Dynamic and Molecular Mechanics Poisson-Boltzmann Surface Area simulations (MM-PBSA) demonstrated that the ACE/BBP-BrachyNH₂ complex showed lower binding and van der Wall energies than the ACE/des-Pro⁸-BPP-BrachyNH₂ complex, therefore having better stability. The removal of the N-terminal tryptophan increased the in silico predicted toxicological effects and cytotoxicity when compared with BPP-BrachyNH₂ or des-Pro⁸-BPP-BrachyNH₂. Otherwise, des-Pro⁸-BPP-BrachyNH₂ was 190-fold less cytotoxic than BPP-BrachyNH₂. Thus, the removal of C-terminal proline residue was able to markedly decrease both the BPP-BrachyNH₂-induced ACE inhibitory and cytotoxic effects assessed by in vitro and in silico approaches. In conclusion, the aminoacid sequence of BPP-BrachyNH₂ is essential for its ACE inhibitory activity and associated with an acceptable toxicological profile. The perspective of the interactions of BPP-BrachyNH₂ with ACE found in the present study can be used for development of drugs with differential therapeutic profile than current ACE inhibitors.

Protease Inhibitors Extracted from Caesalpinia echinata Lam. Affect Kinin Release during Lung Inflammation

Inflammation is an essential process in many pulmonary diseases in which kinins are generated by protease action on kininogen, a phenomenon that is blocked by protease inhibitors. We evaluated kinin release in an in vivo lung inflammation model in rats, in the presence or absence of CeKI (C. echinata kallikrein inhibitor), a plasma kallikrein, cathepsin G, and proteinase-3 inhibitor, and rCeEI (recombinant C. echinata elastase inhibitor), which inhibits these proteases and also neutrophil elastase. Wistar rats were intravenously treated with buffer (negative control) or inhibitors and, subsequently, lipopolysaccharide was injected into their lungs. Blood, bronchoalveolar lavage fluid (BALF), and lung tissue were collected. In plasma, kinin release was higher in the LPS-treated animals in comparison to CeKI or rCeEI groups. rCeEI-treated animals presented less kinin than CeKI-treated group. Our data suggest that kinins play a pivotal role in lung inflammation and may be generated by different enzymes; however, neutrophil elastase seems to be the most important in the lung tissue context. These results open perspectives for a better understanding of biological process where neutrophil enzymes participate and indicate these plant inhibitors and their recombinant correlates for therapeutic trials involving pulmonary diseases.

Insights into the Hypertensive Effects of Tityus serrulatus Scorpion Venom: Purification of an Angiotensin-Converting Enzyme-Like Peptidase

The number of cases of envenomation by scorpions has grown significantly in Brazil since 2007, with the most severe cases being caused by the Tityus serrulatus scorpion. Although envenomed patients mostly suffer neurotoxic manifestations, other symptoms, such as hypertension, cannot be exclusively attributed to neurotoxins. Omics analyses have detected plentiful amounts of metalloproteases in T. serrulatus venom. However, the roles played by these enzymes in envenomation are still unclear. Endeavoring to investigate the functions of scorpion venom proteases, we describe here for the first time an Angiotensin I-Converting Enzyme-like peptidase (ACE-like) purified from T. serrulatus venom. The crude venom cleaved natural and fluorescent substrates and these activities were inhibited by captopril. Regarding the serum neutralization, the scorpion antivenom was more effective at blocking the ACE-like activity than arachnid antivenom, although neither completely inhibited the venom cleavage action, even at higher doses. ACE-like was purified from the venom after three chromatographic steps and its identity was confirmed by mass spectrometric and transcriptomic analyses. Bioinformatics analysis showed homology between the ACE-like transcript sequences from Tityus spp. and human testis ACE. These findings advance our understanding of T. serrulatus venom components and may improve treatment of envenomation victims, as ACE-like may contribute to envenomation symptoms, especially the resulting hypertension.

The influence of angiotensin converting enzyme mutations on the kinetics and dynamics of N-domain selective inhibition

Angiotensin-1-converting enzyme (ACE) is a zinc metalloprotease that plays a major role in blood pressure regulation via the renin-angiotensin-aldosterone system. ACE consists of two domains with differences in inhibitor binding affinities despite their 90% active site identity. While the C-domain primarily controls blood pressure, the N-domain is selective for cleavage of the antifibrotic N-acetyl-Ser-Asp-Lys-Pro. Inhibitors, such as 33RE, that selectively bind to the N-domain thus show potential for treating fibrosis without affecting blood pressure. The aim of this study was to elucidate the molecular mechanism of this selectivity. ACE inhibition by 33RE was characterized using a continuous kinetic assay with fluorogenic substrate. The N-domain displayed nanomolar (K_i = 11.21 ± 0.74 nm) and the C-domain micromolar (K_i = 11 278 ± 410 nm) inhibition, thus 1000-fold selectivity. Residues predicted to contribute to selectivity based on the N-domain-33RE co-crystal structure were subsequently mutated to their C-domain counterparts. S₂ subsite mutation with resulting loss of a hydrogen bond drastically decreased the affinity (K_i = 2 794 ± 156 nm), yet did not entirely account for selectivity. Additional substitution of all unique S₂ ' residues, however, completely abolished selectivity (K_i = 10 009 ± 157 nm). Interestingly, these residues do not directly bind 33RE. All mutants were therefore subjected to molecular dynamics simulations in the presence and absence of 33RE. Trajectory analyses highlighted the importance of these S₂ ' residues in formation of a favourable interface between the ACE subdomains and thus a closed, ligand-bound complex. This study provides a molecular basis for the intersubsite synergism governing 33RE's 1000-fold N-selectivity and aids the future design of novel inhibitors for fibrosis treatment.

ENZYMES

Angiotensin converting enzyme (ACE, EC 3.4.15.1).

Kinetic and structural characterization of amyloid-β peptide hydrolysis by human angiotensin-1-converting enzyme

Angiotensin‐1‐converting enzyme (ACE), a zinc metallopeptidase, consists of two homologous catalytic domains (N and C) with different substrate specificities. Here we report kinetic parameters of five different forms of human ACE with various amyloid beta (Aβ) substrates together with high resolution crystal structures of the N‐domain in complex with Aβ fragments. For the physiological Aβ(1–16) peptide, a novel ACE cleavage site was found at His14‐Gln15. Furthermore, Aβ(1–16) was preferentially cleaved by the individual N‐domain; however, the presence of an inactive C‐domain in full‐length somatic ACE (sACE) greatly reduced enzyme activity and affected apparent selectivity. Two fluorogenic substrates, Aβ(4–10)Q and Aβ(4–10)Y, underwent endoproteolytic cleavage at the Asp7‐Ser8 bond with all ACE constructs showing greater catalytic efficiency for Aβ(4–10)Y. Surprisingly, in contrast to Aβ(1–16) and Aβ(4–10)Q, sACE showed positive domain cooperativity and the double C‐domain (CC‐sACE) construct no cooperativity towards Aβ(4–10)Y. The structures of the Aβ peptide–ACE complexes revealed a common mode of peptide binding for both domains which principally targets the C‐terminal P2′ position to the S2′ pocket and recognizes the main chain of the P1′ peptide. It is likely that N‐domain selectivity for the amyloid peptide is conferred through the N‐domain specific S2′ residue Thr358. Additionally, the N‐domain can accommodate larger substrates through movement of the N‐terminal helices, as suggested by the disorder of the hinge region in the crystal structures. Our findings are important for the design of domain selective inhibitors as the differences in domain selectivity are more pronounced with the truncated domains compared to the more physiological full‐length forms.

Database

The atomic coordinates and structure factors for N‐domain ACE with Aβ peptides 4–10 (5AM8), 10–16 (5AM9), 1–16 (5AMA), 35–42 (5AMB) and (4–10)Y (5AMC) complexes have been deposited in the Protein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers University, New Brunswick, NJ, USA (http://www.rcsb.org/).

Structural basis of Ac-SDKP hydrolysis by Angiotensin-I converting enzyme

Angiotensin-I converting enzyme (ACE) is a zinc dipeptidylcarboxypeptidase with two active domains and plays a key role in the regulation of blood pressure and electrolyte homeostasis, making it the principal target in the treatment of cardiovascular disease. More recently, the tetrapetide N-acetyl-Ser–Asp–Lys–Pro (Ac-SDKP) has emerged as a potent antifibrotic agent and negative regulator of haematopoietic stem cell differentiation which is processed exclusively by ACE. Here we provide a detailed biochemical and structural basis for the domain preference of Ac-SDKP. The high resolution crystal structures of N-domain ACE in complex with the dipeptide products of Ac-SDKP cleavage were obtained and offered a template to model the mechanism of substrate recognition of the enzyme. A comprehensive kinetic study of Ac-SDKP and domain co-operation was performed and indicated domain interactions affecting processing of the tetrapeptide substrate. Our results further illustrate the molecular basis for N-domain selectivity and should help design novel ACE inhibitors and Ac-SDKP analogues that could be used in the treatment of fibrosis disorders.

New proline-rich oligopeptides from the venom of African adders: Insights into the hypotensive effect of the venoms

BACKGROUND

The snakes from the Bitis genus are some of the most medically important venomous snakes in sub Saharan Africa, however little is known about the composition and effects of these snake venom peptides. Considering that the victims with Bitis genus snakes have exacerbate hypotension and cardiovascular disorders, we investigated here the presence of angiotensin-converting enzyme modulators on four different species of venoms.

METHODS

The peptide fractions from Bitis gabonica gabonica, Bitis nasicornis, Bitis gabonica rhinoceros and Bitis arietans which showed inhibitory activity on angiotensin-converting enzyme were subjected to mass spectrometry analysis. Eight proline-rich peptides were synthetized and their potencies were evaluated in vitro and in vivo.

RESULTS

The MS analysis resulted in over 150 sequences, out of which 32 are new proline-rich oligopeptides, and eight were selected for syntheses. For some peptides, inhibition assays showed inhibitory potentials of cleavage of angiotensin I ten times greater when compared to bradykinin. In vivo tests showed that all peptides decreased mean arterial pressure, followed by tachycardia in 6 out of 8 of the tests.

CONCLUSION

We describe here some new and already known proline-rich peptides, also known as bradykinin-potentiating peptides. Four synthetic peptides indicated a preferential inhibition of angiotensin-converting enzyme C-domain. In vivo studies show that the proline-rich oligopeptides are hypotensive molecules.

GENERAL SIGNIFICANCE

Although proline-rich oligopeptides are known molecules, we present here 32 new sequences that are inhibitors of the angiotensin-converting enzyme and consistent with the symptoms of the victims of Bitis spp, who display severe hypotension.

African adders: partial characterization of snake venoms from three Bitis species of medical importance and their neutralization by experimental equine antivenoms

BACKGROUND

An alarming number of fatal accidents involving snakes are annually reported in Africa and most of the victims suffer from permanent local tissue damage and chronic disabilities. Envenomation by snakes belonging to the genus Bitis, Viperidae family, are common in Sub-Saharan Africa. The accidents are severe and the victims often have a poor prognosis due to the lack of effective specific therapies. In this study we have biochemically characterized venoms from three different species of Bitis, i.e., Bitis arietans, Bitis gabonica rhinoceros and Bitis nasicornis, involved in the majority of the human accidents in Africa, and analyzed the in vitro neutralizing ability of two experimental antivenoms.

METHODOLOGY/PRINCIPAL FINDINGS

The data indicate that all venoms presented phospholipase, hyaluronidase and fibrinogenolytic activities and cleaved efficiently the FRET substrate Abz-RPPGFSPFRQ-EDDnp and angiotensin I, generating angiotensin 1-7. Gelatinolytic activity was only observed in the venoms of B. arietans and B. nasicornis. The treatment of the venoms with protease inhibitors indicated that Bitis venoms possess metallo and serinoproteases enzymes, which may be involved in the different biological activities here evaluated. Experimental antivenoms produced against B. arietans venom or Bitis g. rhinoceros plus B. nasicornis venoms cross-reacted with the venoms from the three species and blocked, in different degrees, all the enzymatic activities in which they were tested.

CONCLUSION

These results suggest that the venoms of the three Bitis species, involved in accidents with humans in the Sub-Saharan Africa, contain a mixture of various enzymes that may act in the generation and development of some of the clinical manifestations of the envenomations. We also demonstrated that horse antivenoms produced against B. arietans or B. g. rhinoceros plus B. nasicornis venoms can blocked some of the toxic activities of these venoms.

Characterization of angiotensin I-converting enzyme from anterior gills of the mangrove crab Ucides cordatus

Angiotensin I-converting enzyme (ACE) is a well-known metallopeptidase that is found in vertebrates, invertebrates and bacteria. We isolated from the anterior gill of the crab Ucides cordatus an isoform of ACE, here named crab-ACE, which presented catalytic properties closely resembling to those of mammalian ACE. The enzyme was purified on Sepharose-lisinopril affinity chromatography to apparent homogeneity and a band of about 72 kDa could be visualized after silver staining and Western blotting. Assays performed with fluorescence resonance energy transfer (FRET) selective ACE substrates Abz-FRK(Dnp)P-OH, Abz-SDK(Dnp)P-OH and Abz-LFK(Dnp)-OH, allowed us to verify that crab-ACE has hydrolytic profile very similar to that of the ACE C-domain. In addition, we observed that crab-ACE can hydrolyze the ACE substrates, angiotensin I and bradykinin. The enzyme was strongly inhibited by the specific ACE inhibitor lisinopril (Ki of 1.26 nM). However, in contrast to other ACE isoforms, crab-ACE presented a very particular optimum pH, being the substrate Abz-FRK(Dnp)-P-OH hydrolyzed efficiently at pH 9.5. Other interesting characteristic of crab-ACE was that the maximum hydrolytic activity was reached at around 45°C. The description of an ACE isoform in Ucides cordatus is challenging and may contribute to a better understanding of the biochemical function of this enzyme in invertebrates.

Purification and biochemical characterization of a fibrin(ogen)olytic metalloprotease from Macrovipera mauritanica snake venom which induces vascular permeability

In the present study, a novel fibrin(ogen)olytic metalloprotease from Macrovipera mauritanica snake venom was purified and characterized in terms of enzyme kinetics and substrate specificity. The purified enzyme [termed snake venom metalloprotease-Macrovipera mauritanica (SVMP‑MM)] was composed of a single polypeptide with an apparent molecular weight of 27 kDa, as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The N-terminus of the enzyme was composed of NH(2)-QRFAPRYIEL-COOH, as determined by N-terminal sequencing. The Aα- and the Bβ-chains of fibrinogen were completely cleaved by SVMP-MM within 20 and 480 min, respectively. However, the γ-chain was much more resistant to digestion by the enzyme. The enzyme also exhibited proteolytic activity, cleaving the α-α polymer of cross-linked fibrin, but did not effectively digest the γ-γ polymer. To determine the kinetic parameters for SVMP-MM, a fluorescence-quenching peptide (termed o-aminobenzoic acid-HTEKLVTS-2,4-dinitrophenyl‑NH(2)) containing a K-L sequence for SVMP-MM cleavage was designed and synthesized. The optimal pH and temperature for the enzyme activity were found to be 5.5 and 37˚C, respectively, when the fluorogenic substrate was synthesized and used as a substrate. Among the various divalent cations tested, Ni(2+) and Cu(2+) showed strong inhibitory effects on enzyme activity, with an average of 69.6% inhibition. The enzyme activity was also inhibited by treatment with 1,10-phenanthroline, ethylenediaminetetraacetic acid and glycol-bis-(2‑aminoethylether)-N,N,N',N'-tetra-acetic acid, but not with aprotinin, tosyl-lysine chloromethyl ketone and tosyl-phenylalanyl chloromethyl ketone, suggesting that SVMP-MM is a metalloprotease and not a serine protease. The enzymatic parameters, including the K(M), k(cat), and k(cat)/K(M) values were estimated to be 0.015 mM, 0.031 sec(-1), and 20.67 mM(-1)sec(-1), respectively. SVMP-MM induced vascular permeability by digesting type IV collagen. The results obtained in our study demonstrate that SVMP-MM is a fibrin(ogen)olytic P-I class metalloprotease, which can induce a hemorrhagic reaction in vivo.

A novel aggregation-induced emission based fluorescent probe for an angiotensin converting enzyme (ACE) assay and inhibitor screening

A novel ‘turn-on’ fluorescent probe with the aggregation-induced emission (AIE) property for an ACE assay.

P-I class metalloproteinase from Bothrops moojeni venom is a post-proline cleaving peptidase with kininogenase activity: insights into substrate selectivity and kinetic behavior

Snake venom metalloproteinases (SVMPs) belonging to P-I class are able to hydrolyze extracellular matrix proteins and coagulation factors triggering local and systemic reactions by multiple molecular mechanisms that are not fully understood. BmooMPα-I, a P-I class SMVP from Bothrops moojeni venom, was active upon neuro- and vaso-active peptides including angiotensin I, bradykinin, neurotensin, oxytocin and substance P. Interestingly, BmooMPα-I showed a strong bias towards hydrolysis after proline residues, which is unusual for most of characterized peptidases. Moreover, the enzyme showed kininogenase activity similar to that observed in plasma and cells by kallikrein. FRET peptide assays indicated a relative promiscuity at its S2-S'2 subsites, with proline determining the scissile bond. This unusual post-proline cleaving activity was confirmed by the efficient hydrolysis of the synthetic combinatorial library MCA-GXXPXXQ-EDDnp, described as resistant for canonical peptidases, only after Pro residues. Structural analysis of the tripeptide LPL complexed with BmooMPα-I, generated by molecular dynamics simulations, assisted in defining the subsites and provided the structural basis for subsite preferences such as the restriction of basic residues at the S2 subsite due to repulsive electrostatic effects and the steric impediment for large aliphatic or aromatic side chains at the S1 subsite. These new functional and structural findings provided a further understanding of the molecular mechanisms governing the physiological effects of this important class of enzymes in envenomation process.

N- versus C-domain selectivity of catalytic inactivation of human angiotensin converting enzyme by lisinopril-coupled transition metal chelates

The N- and C-terminal domains of human somatic angiotensin I converting enzyme (sACE-1) demonstrate distinct physiological functions, with resulting interest in the development of domain-selective inhibitors for specific therapeutic applications. Herein, the activity of lisinopril-coupled transition metal chelates was tested for both reversible binding and irreversible catalytic inactivation of each domain of sACE-1. C/N domain binding selectivity ratios ranged from 1 to 350, while rates of irreversible catalytic inactivation of the N- and C-domains were found to be significantly greater for the N-domain, suggesting a more optimal orientation of M-chelate-lisinopril complexes within the active site of the N-domain of sACE-1. Finally, the combined effect of binding selectivity and inactivation selectivity was assessed for each catalyst (double-filter selectivity factors), and several catalysts were found to cause domain-selective catalytic inactivation. The results of this study demonstrate the ability to optimize the target selectivity of catalytic metallopeptides through both binding and catalytic factors (double-filter effect).

P-I snake venom metalloproteinase is able to activate the complement system by direct cleavage of central components of the cascade

BACKGROUND

Snake Venom Metalloproteinases (SVMPs) are amongst the key enzymes that contribute to the high toxicity of snake venom. We have recently shown that snake venoms from the Bothrops genus activate the Complement system (C) by promoting direct cleavage of C-components and generating anaphylatoxins, thereby contributing to the pathology and spread of the venom. The aim of the present study was to isolate and characterize the C-activating protease from Bothrops pirajai venom.

RESULTS

Using two gel-filtration chromatography steps, a metalloproteinase of 23 kDa that activates Complement was isolated from Bothrops pirajai venom. The mass spectrometric identification of this protein, named here as C-SVMP, revealed peptides that matched sequences from the P-I class of SVMPs. C-SVMP activated the alternative, classical and lectin C-pathways by cleaving the α-chain of C3, C4 and C5, thereby generating anaphylatoxins C3a, C4a and C5a. In vivo, C-SVMP induced consumption of murine complement components, most likely by activation of the pathways and/or by direct cleavage of C3, leading to a reduction of serum lytic activity.

CONCLUSION

We show here that a P-I metalloproteinase from Bothrops pirajai snake venom activated the Complement system by direct cleavage of the central C-components, i.e., C3, C4 and C5, thereby generating biologically active fragments, such as anaphylatoxins, and by cleaving the C1-Inhibitor, which may affect Complement activation control. These results suggest that direct complement activation by SVMPs may play a role in the progression of symptoms that follow envenomation.

Novel approaches for the identification of inhibitors of leishmanial dipeptidylcarboxypeptidase

INTRODUCTION

Leishmaniasis imposes a substantial burden of mortality and morbidity affecting 12 million globally and continues to be a neglected tropical disease. Control of the disease is mainly based on chemotherapy, which relies on a handful of drugs with serious limitations. Over the last decade, target-based drug discovery is also being employed in addition to the random screening of compounds. Leishmanial dipeptidylcarboxypeptidase (LDCP), an angiotensin converting enzyme (ACE) related metallopeptidase, has been recently identified as a novel drug target for antileishmanial chemotherapy.

AREAS COVERED

This article examines dipeptidylcarboxypeptidase (DCP) of Leishmania donovani and of other sources from the international literature regarding their biochemical and structural characterization in comparison to mammalian ACE. Furthermore, the author discusses the identification of LdDCP specific inhibitors by virtual screening and their effect on parasite multiplication. Finally, the review looks ahead at areas for further exploration of DCP inhibitors in Leishmania chemotherapy.

EXPERT OPINION

The first step in targeted screening is to identify a suitable drug target and its validation followed by its use in high throughput screening of compounds. Limited studies on LDCP inhibitors have established a good correlation between parasite enzyme inhibition and their biological activity. This suggests that there is a potential for LDCP inhibitors as new antileishmanial drugs.

Substrate specificity and the effect of calcium on Trypanosoma brucei metacaspase 2

Metacaspases are cysteine peptidases found only in yeast, plants and lower eukaryotes, including the protozoa. To investigate the extended substrate specificity and effects of Ca(2+) on the activation of these enzymes, detailed kinetic, biochemical and structural analyses were carried out on metacaspase 2 from Trypanosoma brucei (TbMCA2). These results reveal that TbMCA2 has an unambiguous preference for basic amino acids at the P1 position of peptide substrates and that this is most probably a result of hydrogen bonding from the P1 residue to Asp95 and Asp211 in TbMCA2. In addition, TbMCA2 also has a preference for charged residues at the P2 and P3 positions and for small residues at the prime side of a peptide substrate. Studies into the effects of Ca(2+) on the enzyme revealed the presence of two Ca(2+) binding sites and a reversible structural modification of the enzyme upon Ca(2+) binding. In addition, the concentration of Ca(2+) used for activation of TbMCA2 was found to produce a differential effect on the activity of TbMCA2, but only when a series of peptides that differed in P2 were examined, suggesting that Ca(2+) activation of TbMCA2 has a structural effect on the enzyme in the vicinity of the S2 binding pocket. Collectively, these data give new insights into the substrate specificity and Ca(2+) activation of TbMCA2. This provides important functional details and leads to a better understanding of metacaspases, which are known to play an important role in trypanosomes and make attractive drug targets due to their absence in humans.

A modern understanding of the traditional and nontraditional biological functions of angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is a zinc-dependent peptidase responsible for converting angiotensin I into the vasoconstrictor angiotensin II. However, ACE is a relatively nonspecific peptidase that is capable of cleaving a wide range of substrates. Because of this, ACE and its peptide substrates and products affect many physiologic processes, including blood pressure control, hematopoiesis, reproduction, renal development, renal function, and the immune response. The defining feature of ACE is that it is composed of two homologous and independently catalytic domains, the result of an ancient gene duplication, and ACE-like genes are widely distributed in nature. The two ACE catalytic domains contribute to the wide substrate diversity of ACE and, by extension, the physiologic impact of the enzyme. Several studies suggest that the two catalytic domains have different biologic functions. Recently, the X-ray crystal structure of ACE has elucidated some of the structural differences between the two ACE domains. This is important now that ACE domain-specific inhibitors have been synthesized and characterized. Once widely available, these reagents will undoubtedly be powerful tools for probing the physiologic actions of each ACE domain. In turn, this knowledge should allow clinicians to envision new therapies for diseases not currently treated with ACE inhibitors.

Peptidomics of three Bothrops snake venoms: insights into the molecular diversification of proteomes and peptidomes

Snake venom proteomes/peptidomes are highly complex and maintenance of their integrity within the gland lumen is crucial for the expression of toxin activities. There has been considerable progress in the field of venom proteomics, however, peptidomics does not progress as fast, because of the lack of comprehensive venom sequence databases for analysis of MS data. Therefore, in many cases venom peptides have to be sequenced manually by MS/MS analysis or Edman degradation. This is critical for rare snake species, as is the case of Bothrops cotiara (BC) and B. fonsecai (BF), which are regarded as near threatened with extinction. In this study we conducted a comprehensive analysis of the venom peptidomes of BC, BF, and B. jararaca (BJ) using a combination of solid-phase extraction and reversed-phase HPLC to fractionate the peptides, followed by nano-liquid chromatography-tandem MS (LC-MS/MS) or direct infusion electrospray ionization-(ESI)-MS/MS or MALDI-MS/MS analyses. We detected marked differences in the venom peptidomes and identified peptides ranging from 7 to 39 residues in length by de novo sequencing. Forty-four unique sequences were manually identified, out of which 30 are new peptides, including 17 bradykinin-potentiating peptides, three poly-histidine-poly-glycine peptides and interestingly, 10 L-amino acid oxidase fragments. Some of the new bradykinin-potentiating peptides display significant bradykinin potentiating activity. Automated database search revealed fragments from several toxins in the peptidomes, mainly from l-amino acid oxidase, and allowed the determination of the peptide bond specificity of proteinases and amino acid occurrences for the P4-P4' sites. We also demonstrate that the venom lyophilization/resolubilization process greatly increases the complexity of the peptidome because of the imbalance caused to the venom proteome and the consequent activity of proteinases on venom components. The use of proteinase inhibitors clearly showed different outcomes in the peptidome characterization and suggested that degradomic-peptidomic analysis of snake venoms is highly sensitive to the conditions of sampling procedures.

Three key proteases--angiotensin-I-converting enzyme (ACE), ACE2 and renin--within and beyond the renin-angiotensin system

The discovery of angiotensin-I-converting enzyme 2 (ACE2) and a (pro)renin receptor has renewed interest in the physiology of the renin-angiotensin system (RAS). Through the ACE2/angiotensin-(1–7)/Mas counter-regulatory axis, ACE2 balances the vasoconstrictive, proliferative, fibrotic and proinflammatory effects of the ACE/angiotensin II/AT1 axis. The (pro)renin receptor system shows an angiotensin-dependent function related to increased generation of angiotensin I, and an angiotensin-independent aspect related to intracellular signalling. Activation of ACE2 and inhibition of ACE and renin have been at the core of the RAS regulation. The aim of this review is to discuss the biochemistry and biological functions of ACE, ACE2 and renin within and beyond the RAS, and thus provide a perspective for future bioactives from natural plant and/or food resources related to the three proteases.

Characterization of the M32 metallocarboxypeptidase of Trypanosoma brucei: differences and similarities with its orthologue in Trypanosoma cruzi

Metallocarboxypeptidases (MCP) of the M32 family of peptidases have been identified in a number of prokaryotic organisms but they are absent from eukaryotic genomes with the remarkable exception of those of trypanosomatids. The genome of Trypanosoma brucei, the causative agent of Sleeping Sickness, encodes one such MCP which displays 72% identity to the characterized TcMCP-1 from Trypanosoma cruzi. As its orthologue, TcMCP-1, Trypanosoma brucei MCP is a cytosolic enzyme expressed in both major stages of the parasite. Purified recombinant TbMCP-1 exhibits a significant hydrolytic activity against the carboxypeptidase B substrate FA (furylacryloil)-Ala-Lys at pH 7.0-7.8 resembling the T. cruzi enzyme. Several divalent cations had little effect on TbMCP-1 activity but increasing amounts of Co(2+) inhibited the enzyme. Despite having similar tertiary structure, both protozoan MCPs display different substrate specificity with respect to P1 position. Thus, TcMCP-1 enzyme cleaved Abz-FVK-(Dnp)-OH substrate (where Abz: o-aminobenzoic acid and Dnp: 2,4-dinitrophenyl) whereas TbMCP-1 had no activity on this substrate. Comparative homology models and sequence alignments using TcMCP-1 as a template led us to map several residues that could explain this difference. To verify this hypothesis, site-directed mutagenesis was undertaken replacing the TbMCP-1 residues by those present in TcMCP-1. We found that the substitution A414M led TbMCP-1 to gain activity on Abz-FVK-(Dnp)-OH, thus showing that this residue is involved in specificity determination, probably being part of the S1 sub-site. Moreover, the activity of both protozoan MCPs was explored on two vasoactive compounds such as bradykinin and angiotensin I resulting in two different hydrolysis patterns.

Development of on-line high performance liquid chromatography (HPLC)-biochemical detection methods as tools in the identification of bioactives

Biochemical detection (BCD) methods are commonly used to screen plant extracts for specific biological activities in batch assays. Traditionally, bioactives in the most active extracts were identified through time-consuming bio-assay guided fractionation until single active compounds could be isolated. Not only are isolation procedures often tedious, but they could also lead to artifact formation. On-line coupling of BCD assays to high performance liquid chromatography (HPLC) is gaining ground as a high resolution screening technique to overcome problems associated with pre-isolation by measuring the effects of compounds post-column directly after separation. To date, several on-line HPLC-BCD assays, applied to whole plant extracts and mixtures, have been published. In this review the focus will fall on enzyme-based, receptor-based and antioxidant assays.

Premolis semirufa (Walker, 1856) envenomation, disease affecting rubber tappers of the Amazon: searching for caterpillar-bristles toxic components

BACKGROUND

The caterpillar of the moth Premolis semirufa (Lepidoptera: Arctiidae), commonly named Pararama, is endemic of the Amazon basin. Accidental contact with these caterpillar bristles causes local symptoms such as intense heat, pain, edema and itching which last for three to seven days; however, after multiples contacts, it may induce joint-space narrowing and bone alteration, as well as degeneration of the articular cartilage and immobilization of the affected joints. Specific treatment for this disease does not exist, but corticosteroids are frequently administered. Despite of the public health hazard of Premolis semirufa caterpillar poisoning, little is known about the nature of the toxic components involved in the induction of the pathology.

METHODOLOGY/PRINCIPAL FINDINGS

Here we have investigated the biological and immunochemical characteristics of the caterpillar's bristles components. Analysis of the bristles extract in in vitro assays revealed the presence of proteolytic and hyaluronidase activities but no phospholipase A(2) activity. In vivo, it was observed that the bristles extract is not lethal but can induce an intense inflammatory process, characterized by the presence of neutrophils in the paw tissues of injected mice. Furthermore, the bristles components stimulated an intense and specific antibody response but autoantibodies such as anti-DNA or anti-collagen type II were not detected.

CONCLUSION

The results suggest that Premolis semirufa caterpillar bristles secretion contains a mixture of different enzymes that may act together in the generation and development of the clinical manifestations of the Pararama envenomation. Moreover, the high immunogenicity of the caterpillar bristles components, as shown by the generation of high antibody titers, may also contribute to the induction and establishment of the inflammatory disease.

Angiotensin-degrading serine peptidase: a new chymotrypsin-like activity in the venom of Bothrops jararaca partially blocked by the commercial antivenom

Snakebite envenomation is considered a highly relevant public health hazard in South America, having an impact in terms of mortality and morbidity. In Brazil, Bothrops (sensu latu) poisoning is responsible for 90% of the snakebites and in patients treated at the Vital Brazil Hospital (Butantan Institute) this index reaches 97.5%. The objective of the present study was to analyze more specifically the ability of the antibothropic antivenom, produced by the Butantan Institute, São Paulo, Brazil, to neutralize metallo-and serine peptidases, known as the major toxins present in Bothrops jararaca venom. A set of Fret peptides (Free Ressonance Energy Transfer) was studied using the BjV (B. jararaca venom) and site-directed inhibitors PMSF, EDTA and 1,10-phenanthroline. Two substrates were reached to be used as specific tools for studies with metallo peptidases, Abz-FASSAQ-EDDnp, and the serine peptidases, Abz-RPPGFSPFRQ-EDDnp. In disagreement with the literature, the use of both substrates and the antibothropic serum showed a weak neutralization of the serine peptidases present in this venom and a strong neutralization of the metallo peptidases. In order to investigate possible mechanisms of action that have not yet been described for the serine peptidases from the BjV, the present study shows for the first time a new tyrosine-specific chymotrypsin-like and angiotensin-degrading serine peptidase activity, that was partially blocked by the antibothropic serum. In conclusion, the antivenom presented a good neutralization of metallo peptidases but not of serine peptidases, indicating that further studies about serine peptidases immunogenicity are necessary to improve the antibothropic serum.

Foot and mouth disease leader protease (Lbpro): Investigation of prime side specificity allows the synthesis of a potent inhibitor

Foot and mouth disease virus expresses its genetic information as a single polyprotein that is translated from the single-stranded RNA genome. Proteinases contained within the polyprotein then generate the mature viral proteins. The leader protease (Lb(pro)) performs the initial cleavage by freeing itself from the growing polypeptide chain; subsequently, Lb(pro) cleaves the two homologues of the host cell protein eukaryotic initiation factor 4G (eIF4G). We showed that Lb(pro) possesses specific binding sites at the non prime side from S(1) down to S(7) [Santos et al. (2009) Biochemistry, 48, 7948-7958]. Here, we demonstrate that Lb(pro) has high prime side specificity at least down to the S'(5) site. Lb(pro) is thus not only one of the smallest papain-like cysteine peptidases but also one of the most specific. It can still however cleave between both K↓G and G↓R pairs. We further determined the two-step irreversible inhibition (E + I ↔ EI→ E - I) kinetic parameters of two known irreversible epoxide-based inhibitors of cysteine proteinases, E64 and CA074 on Lb(pro) that show for the reversible step (E + I ↔ EI) K(i) = 3.4 μM and 11.6 μM, and for the irreversible step (EI→E-I) k(4) = 0.16 and 0.06 min(-1), respectively. Knowledge of the Lb(pro) specificity led us to extend E64 by addition of the dipeptide R-P. This compound, termed E64-R-P-NH(2), irreversibly inhibited Lb(pro) with a K(i) = 30 nM and k(4) = 0.01 min(-1) and can serve as the basis for design of specific inhibitors of FMDV replication.