Inhibition of aspartic proteases by pepstatin and 3-methylstatine derivatives of pepstatin. Evidence for collected-substrate enzyme inhibition

Ribosomal Synthesis of Peptides Bearing Noncanonical Backbone Structures via Chemical Posttranslational Modifications

Noncanonical peptide backbone structures, such as heterocycles and non-α-amino acids, are characteristic building blocks present in peptidic natural products. To achieve ribosomal synthesis of designer peptides bearing such noncanonical backbone structures, we have devised translation-compatible precursor residues and their chemical posttranslational modification processes. In this chapter, we describe the detailed procedures for the in vitro translation of peptides containing the precursor residues by means of genetic code reprogramming technology and posttranslational generation of objective noncanonical backbone structures.

Post-translational backbone-acyl shift yields natural product-like peptides bearing hydroxyhydrocarbon units

Hydroxyhydrocarbon (Hhc) moieties in the backbone of peptidic natural products can exert a substantial influence on the bioactivities of the products, making Hhc units an attractive class of building blocks for de novo peptides. However, despite advances in in vitro genetic code reprogramming, the ribosomal incorporation of Hhc units remains challenging. Here we report a method for in vitro ribosomal synthesis of natural-product-like peptides bearing Hhc units. A series of azide/hydroxy acids were designed as chemical precursors of Hhc units and incorporated into the nascent peptide chain by means of genetic code reprogramming. Post-translational reduction of the azide induced an O-to-N acyl shift to rearrange the peptide backbone. This method allows for one-pot ribosomal synthesis of designer macrocycles bearing various β-, γ- and δ-type Hhc units. We also report the synthesis of a statine-containing peptidomimetic inhibitor of β-secretase 1 as a showcase example.

Adjunctive application of solid-state culture products and its freeze-dried powder from Aspergillus sojae for semi-hard cheese

BACKGROUND

Species belonging to the genus Aspergillus have been used in traditional Japanese fermented foods. Aspergillus sojae is a species responsible for strong proteolytic activity. Freeze-drying treatments followed by physical disruption enables the pulverization of the mycelia of A. sojae RIB 1045 grown in whey protein-base solid media. Intracellular proteases were extracted using this protocol to compare extracellular protease activity in terms of the reaction's pH dependence in the presence or absence of inhibitors.

RESULT

With different sensitivities to inhibitors, intracellular and extracellular proteases showed the strongest activity under acidic conditions, which were considered suitable for cheese application. The raw culture product (CP) and its freeze-dried product (FDP) were mixed with cheese curds, prepared according to Gouda-type cheese-making methods, and were allowed to ripen for 3 months. Chemical analysis of the products showed 13.3% water-soluble nitrogen (WSN) in the control, which had received noncultured media, whereas 20.0% and 21.1% WSN was found in the CP and FDP experimental cheeses, respectively. Although these adjuncts significantly increased WSN, an insignificant difference was found between CP and FDP. Free fatty acids in all experimental cheeses were similar, showing that CP and FDP caused no rancid defects.

CONCLUSION

The introduction of freeze-drying treatments accompanied by cell disruption resulted in a negligible effect in terms of WSN. However, the application of A. sojae can be beneficial when it comes to increasing the level of WSN compared with A. oryzae, as shown in our previous study. © 2020 Society of Chemical Industry.

INFOGEST static in vitro simulation of gastrointestinal food digestion

Developing a mechanistic understanding of the impact of food structure and composition on human health has increasingly involved simulating digestion in the upper gastrointestinal tract. These simulations have used a wide range of different conditions that often have very little physiological relevance, and this impedes the meaningful comparison of results. The standardized protocol presented here is based on an international consensus developed by the COST INFOGEST network. The method is designed to be used with standard laboratory equipment and requires limited experience to encourage a wide range of researchers to adopt it. It is a static digestion method that uses constant ratios of meal to digestive fluids and a constant pH for each step of digestion. This makes the method simple to use but not suitable for simulating digestion kinetics. Using this method, food samples are subjected to sequential oral, gastric and intestinal digestion while parameters such as electrolytes, enzymes, bile, dilution, pH and time of digestion are based on available physiological data. This amended and improved digestion method (INFOGEST 2.0) avoids challenges associated with the original method, such as the inclusion of the oral phase and the use of gastric lipase. The method can be used to assess the endpoints resulting from digestion of foods by analyzing the digestion products (e.g., peptides/amino acids, fatty acids, simple sugars) and evaluating the release of micronutrients from the food matrix. The whole protocol can be completed in ~7 d, including ~5 d required for the determination of enzyme activities.

Primary structures of different isoforms of buffalo pregnancy-associated glycoproteins (BuPAGs) during early pregnancy and elucidation of the 3-dimensional structure of the most abundant isoform BuPAG 7

Pregnancy-associated glycoproteins (PAGs) are expressed during pregnancy by the trophoectodermal cells of fetus. Presence of PAGs in dam's circulation has been widely used in pregnancy diagnosis. The present study reports the identification and characterization of different PAG isoforms in buffalo during early stages of pregnancy. The PAG mRNAs isolated from fetal cotyledons (Pregnancy stages: 45, 75 and 90 days) were successfully cloned in pJET1.2 vector and transformed in E. coli. A total of 360 random clones were sequenced and correlated with their stages of expression. A total of 12 isoforms namely, BuPAG 1, 2, 4, 6, 7, 8, 9, 13, 15, 16, 18 and one new isoform were identified. BuPAG 7 was found as the most abundant isoform in all three stages followed by BuPAG 18. Further, a large number of variants were found for most of these isoforms. Phylogenetic relationship of identified BuPAGs showed that BuPAG 2 belonged to an ancient group while other members clustered with modern group. Three-dimensional (3D) structure of BuPAG 7 was determined by homology modeling and molecular dynamic (MD) simulations which displayed a typical fold represented by other aspartic proteinase (AP) family members. Molecular docking of Pepstatin inhibitor with BuPAG 7 revealed to interact through various hydrogen bonding and hydrophobic interactions. Various amino acid substitutions were observed in peptide-binding cleft of BuPAG 7. Superimposition of BuPAG 7 with homologous structures revealed the presence of a 35-41 amino acid long insertion (alpha helix connected by two loops) near the N- terminus which seems to be a unique feature of BuPAG 7 in AP family. This is the first report on identification and sequence characterization of PAG isoforms in buffalo with unique finding that these isoforms represent many transcript variants. We also report 3D structure of the most abundant isoform BuPAG 7 for the first time.

DNA-linked Inhibitor Antibody Assay (DIANA) for sensitive and selective enzyme detection and inhibitor screening

Human diseases are often diagnosed by determining levels of relevant enzymes and treated by enzyme inhibitors. We describe an assay suitable for both ultrasensitive enzyme quantification and quantitative inhibitor screening with unpurified enzymes. In the DNA-linked Inhibitor ANtibody Assay (DIANA), the target enzyme is captured by an immobilized antibody, probed with a small-molecule inhibitor attached to a reporter DNA and detected by quantitative PCR. We validate the approach using the putative cancer markers prostate-specific membrane antigen and carbonic anhydrase IX. We show that DIANA has a linear range of up to six logs and it selectively detects zeptomoles of targets in complex biological samples. DIANA's wide dynamic range permits determination of target enzyme inhibition constants using a single inhibitor concentration. DIANA also enables quantitative screening of small-molecule enzyme inhibitors using microliters of human blood serum containing picograms of target enzyme. DIANA's performance characteristics make it a superior tool for disease detection and drug discovery.

Alterations in membrane-associated CD14 expression and the simultaneous liberation of soluble CD14 fragment in adherent macrophages mediated by a leukocyte carboxyl/aspartate protease

Investigations sought to discover the biochemical mechanisms in macrophages that mediate the `shedding' of soluble CD14 fragment. Stimulated macrophages display both increased liberation of soluble CD14 fragment and decreases in residual membrane-associated CD14 complexes following exposure to activating agents ( fMLP/A23187). Application of `class-specific' protease inhibitors revealed that a thiol/cysteine was involved in the biochemical production of soluble CD14 fractions and that a metalloprotease enzymatically degraded soluble CD14 fragment. Exposure of macrophages to individual proteases revealed that both cathepsin-D and elastase promoted variable depletion of membrane-associated CD14 complexes. Additionally, cathepsin-D, and to a lesser extent elastase, generated soluble CD14 fragment. Related studies isolated a carboxyl/aspartate protease from activated macrophages using pepstatin-A affinity chromatography. The physical and functional properties of macrophage pepstatin-A binding protein fractions closely corresponded with the known characteristics of cathepsin-D with respect to: (i) cellular origin; (ii) binding-avidity of carboxyl/aspartate proteases for pepstatin-A; (iii) non-specific proteolysis of haemoglobin detected by Hb-PAGE zymography; and (iv) hydrolysis of a synthetic cathepsin-D-specific peptide substrate. Interpretation of these findings collectively implies that activated leukocytes can biochemically alter membrane-associated CD14 complex expression and promote the liberation of soluble CD14 fragment in both activated and non-activated cell populations.

Aspartic protease inhibitors containing tertiary alcohol transition-state mimics

Aspartic proteases (APs) are a class of enzymes engaged in the proteolytic digestion of peptide substrates. APs play important roles in physiological and infectious pathways, making them plausible drug targets. For instance in the treatment of HIV infections, access to an efficient combination of protease and reverse transcriptase inhibitors have changed a terminal illness to a chronic but manageable disease. However, the benefits have been limited due to the emergence of drug resistant viral strains, poor pharmacokinetic properties of peptidomimetic inhibitors and adverse effects associated with the treatment. In the 1980s, D. Rich and co-workers proposed a novel strategy for the development of AP inhibitors by replacing the secondary hydroxyl group with a tertiary alcohol as part of the transition state (TS) mimicking moiety. This strategy has been extensively explored over the last decade with a common belief that masking of the polar group, e.g. by intramolecular hydrogen bonding, has the potential to enhance transcellular transport. This is the first review presenting the advances of AP inhibitors comprising a tertiary hydroxyl group. The inhibitors have been classified into different tert-hydroxy TS mimics and their design strategies, synthesis, biological activities, structure-activity-relationships and X-ray structures are discussed.

IL-12 and IL-27 regulate the phagolysosomal pathway in mycobacteria-infected human macrophages

BACKGROUND

The cytokine environment at the site of infection is important to the control of mycobacteria by host macrophages. During chronic infection immunosuppressive cytokines are likely to favor mycobacterial growth, persistence, and an avoidance of proper antigen processing and presentation. The activity of interleukin (IL)-27 toward macrophages is anti-inflammatory and this compromises control of mycobacteria. Modulation of the cytokine environment may enhance both protective and vaccine-induced responses.

RESULTS

In this study we showed that supplying IL-12 and neutralizing IL-27 enhanced acidification and fusion of mycobacterial-containing phagosomes with lysosomes. This was achieved by phagosomal acquisition of vacuolar ATPase (V-ATPase) and CD63. Both V-ATPase and CD63 protein levels were increased by the addition of IL-12 and neutralization of IL-27. In addition, cathepsin D associated with the bacteria and matured to the active form when IL-12 was supplied and IL-27 was neutralized. Lysosomal acidification and cathepsin D activity were associated with control of mycobacteria. The acidification of lysosomes, association with mycobacteria, and maturation of cathepsin D required macrophage production of IFN-γ and signaling through signal transducer and activator of transcription (STAT)-1. In contrast, STAT-3 signaling opposed these events.

CONCLUSIONS

Our results have identified novel influences of IL-12, IL-27, and STAT-3 on lysosomal activity and further demonstrate that modulating the cytokine environment promotes enhanced trafficking of mycobacteria to lysosomes in human macrophages. This has important implications in approaches to control infection and improve vaccination. Overcoming bacterial resistance to lysosomal fusion may expand the repertoire of antigens presented to the adaptive arm of the immune response.

Human Ubc9 is involved in intracellular HIV-1 Env stability after trafficking out of the trans-Golgi network in a Gag dependent manner

The cellular E2 Sumo conjugase, Ubc9 interacts with HIV-1 Gag, and is important for the assembly of infectious HIV-1 virions. In the previous study we demonstrated that in the absence of Ubc9, a defect in virion assembly was associated with decreased levels of mature intracellular Envelope (Env) that affected Env incorporation into virions and virion infectivity. We have further characterized the effect of Ubc9 knockdown on HIV Env processing and assembly. We found that gp160 stability in the endoplasmic reticulum (ER) and its trafficking to the trans-Golgi network (TGN) were unaffected, indicating that the decreased intracellular mature Env levels in Ubc9-depleted cells were due to a selective degradation of mature Env gp120 after cleavage from gp160 and trafficked out of the TGN. Decreased levels of Gag and mature Env were found to be associated with the plasma membrane and lipid rafts, which suggest that these viral proteins were not trafficked correctly to the assembly site. Intracellular gp120 were partially rescued when treated with a combination of lysosome inhibitors. Taken together our results suggest that in the absence of Ubc9, gp120 is preferentially degraded in the lysosomes likely before trafficking to assembly sites leading to the production of defective virions. This study provides further insight in the processing and packaging of the HIV-1 gp120 into mature HIV-1 virions.

Mechanistic insights into the inhibition of endo-β 1,4 xyloglucan hydrolase by a classical aspartic protease inhibitor

This is the first report of inactivation of xyloglucanase from Thermomonospora sp by pepstatin A, a specific inhibitor towards aspartic proteases. The steady state kinetics revealed a reversible, competitive, two-step inhibition mechanism with IC 50 and K i values of 3.5 ± 0.5 μM and 1.25 ± 0.5 μM respectively. The rate constants determined for the isomerization of EI to EI(*) and the dissociation of EI* were 14.5 ± 1.5 × 10(-5) s(-1) and 2.85 ± 1.2 × 10(-8) s(-1) respectively, whereas the overall inhibition constant K i(*) was 27 ± 1 nM. The conformational changes induced upon inhibitor binding to xyloglucanase were monitored by fluorescence analysis and the rate constants derived were in agreement with the kinetic data. The abolished isoindole fluorescence of o-phthalaldehyde (OPTA)-labeled xyloglucanase and far UV analysis suggested that pepstatin binds to the active site of the enzyme. Our results revealed that the inactivation of xyloglucanase is due to the interference in the electronic microenvironment and disruption of the hydrogen-bonding network between the essential histidine and other residues involved in catalysis.

Serine protease inhibition by a silanediol peptidomimetic

Silanediol peptidomimetics are demonstrated to inhibit a serine protease. Asymmetric synthesis of the inhibitor was accomplished using Brown hydroboration and CBS reduction of an acylsilane intermediate. The silanediol product was found to inhibit the serine protease chymotrypsin with a K(i) of 107 nM. Inhibition of the enzyme may involve exchange of a silane hydroxyl with the active site serine nucleophile, contrasting with previous silanediol protease inhibitors.

Measurements of the intracellular stability of CPPs

Nowadays, the analysis of the uptake and intracellular distribution of cell-penetrating peptides mostly relies on fluorescence microscopy, using fluorescently labeled CPP analogs. However, fluorescence microscopy does not reveal to which degree fluorescence reflects the intact peptide or only breakdown products. Here, we introduce fluorescence correlation spectroscopy (FCS) as a powerful method to address peptide stability in cells and cell lysates. Measurements in lysates of cells incubated with peptide yield information on degradation of the total cellular peptide content. In combination with protease inhibitors, such measurements enable conclusions on trafficking pathways. Intracellular FCS measurements provide direct information on peptide degradation and association with cellular structures in intact cells.

HIV-1 protease inhibitors with a transition-state mimic comprising a tertiary alcohol: improved antiviral activity in cells

By a small modification in the core structure of the previously reported series of HIV-1 protease inhibitors that encompasses a tertiary alcohol as part of the transition-state mimicking scaffold, up to 56 times more potent compounds were obtained exhibiting EC(50) values down to 3 nM. Three of the inhibitors also displayed excellent activity against selected resistant isolates of HIV-1. The synthesis of 25 new and optically pure HIV-1 protease inhibitors is reported, along with methods for elongation of the inhibitor P1' side chain using microwave-accelerated, palladium-catalyzed cross-coupling reactions, the biological evaluation, and X-ray data obtained from one of the most potent analogues cocrystallized with both the wild type and the L63P, V82T, I84 V mutant of the HIV-1 protease.

Spectral properties and mechanisms that underlie autofluorescent accumulations in Batten disease

Neuronal Ceroid Lipofuscinoses (NCLs) have an incidence of 1 in 12,500 live births. These devastating neurodegenerative lysosomal storage diseases are characterized by the lysosomal accumulation of autofluorescent storage material (AFSM) similar to that seen in aging cells. Using patient derived lymphoblasts from three genetically distinct NCLs we report that AFSM for each NCL has distinct spectral properties. Moreover, by using pharmacological inhibitors to disrupt various biochemical pathways in normal control lymphoblasts we have determined that disruptions in microtubule assembly and non-muscle myosin II function results in accumulation of lysosomal AFSM. Interestingly, inhibition of autophagy did not result in AFSM. We conclude that cellular disturbances outside the lysosome in addition to compromised function of this organelle can result in accumulation of lysosomal AFSM in NCLs and possibly as a result of cellular aging.

Two-carbon-elongated HIV-1 protease inhibitors with a tertiary-alcohol-containing transition-state mimic

A new generation of HIV-1 protease inhibitors encompassing a tertiary-alcohol-based transition-state mimic has been developed. By elongation of the core structure of recently reported inhibitors with two carbon atoms and by varying the P1' group of the compounds, efficient inhibitors were obtained with Ki down to 2.3 nM and EC50 down to 0.17 microM. Two inhibitor-enzyme X-ray structures are reported.

Structure-based specificity mapping of secreted aspartic proteases of Candida parapsilosis, Candida albicans, and Candida tropicalis using peptidomimetic inhibitors and homology modeling

Secreted aspartic proteases (Saps) of pathogenic Candida spp. represent a specific target for antifungal drug development. We synthesized a series of peptidomimetic inhibitors with different isosteric groups and modifications at individual positions and tested them with purified Saps from C. albicans (Sap2p), C. tropicalis (Sapt1p), and C. parapsilosis (Sapp1p). The kinetic parameters indicated that all three proteases prefer binding of inhibitors containing bulky hydrophobic residues between positions P3 and P3'. The most divergent specificity was found for Sapp1p. The sequence alignment of Sap2p, Sapt1p, and Sapp1p, and homology modeling of Sapp1p with the crystal structure of Sapt1p and the complex of Sap2p with a peptidomimetic inhibitor showed that the overall folds of Sap2p, Sapt1p, and Sapp1p are similar. However, the N- and C-terminal loops formed by disulfide bonds between residues 47-53 and 258-292 are significantly shorter in Sapp1p, and a unique insertion following Tyr 129 in Sapp1p results in the formation of a loop that can interact with inhibitor residues. These Sapp1p structural differences might lead to its altered susceptibility to inhibition.

Direct Inhibition of Renin as a Cardiovascular Pharmacotherapy

The important role of renin-angiotensin-aldosterone system blockade in the treatment of systemic hypertension, heart failure, diabetic kidney disease, and atherogenesis has been clearly established. The theoretical therapeutic advantages for inhibiting the detrimental effects of the renin-angiotensin system at its most upstream point have served as the impetus for the development of renin inhibitors. The advent of aliskiren, the first in a novel class of orally active, nonpeptide, highly specific, human renin inhibitors, provides a new modality in the armamentarium of renin-angiotensin system antagonists. Studies in marmosets and rats demonstrated that aliskiren reduced blood pressure in a dose-dependent manner and is highly efficacious in blocking plasma renin activity with parallel reductions in the levels of the other downstream constituents of the renin-angiotensin system. Clinical trials in hypertensive patients have confirmed these benefits with aliskiren whose blood pressure-lowering efficacy is similar to or better than those of standard therapeutic doses of enalapril, losartan, irbesartan, and hydrochlorothiazide. Aliskiren is well tolerated, with few reported adverse effects even at the highest doses tested. Given the established beneficial effects of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers in the treatment of cardiovascular and renovascular diseases, future studies may further elucidate a similar protective role for aliskiren both as a monotherapy and as part of a combination therapy.

Kinetics of intra- and intermolecular zymogen activation with formation of an enzyme-zymogen complex

A mathematical description was made of an autocatalytic zymogen activation mechanism involving both intra- and intermolecular routes. The reversible formation of an active intermediary enzyme-zymogen complex was included in the intermolecular activation route, thus allowing a Michaelis-Menten constant to be defined for the activation of the zymogen towards the active enzyme. Time-concentration equations describing the evolution of the species involved in the system were obtained. In addition, we have derived the corresponding kinetic equations for particular cases of the general model studied. Experimental design and kinetic data analysis procedures to evaluate the kinetic parameters, based on the derived kinetic equations, are suggested. The validity of the results obtained were checked by using simulated progress curves of the species involved. The model is generally good enough to be applied to the experimental kinetic study of the activation of different zymogens of physiological interest. The system is illustrated by following the transformation kinetics of pepsinogen into pepsin.

Trafficking of exogenous peptides into proteasome-dependent major histocompatibility complex class I pathway following enterotoxin B subunit-mediated delivery

The B-subunit component of Escherichia coli heat-labile enterotoxin (EtxB), which binds to cell surface GM1 ganglioside receptors, was recently shown to be a highly effective vehicle for delivery of conjugated peptides into the major histocompatibility complex (MHC) class I pathway. In this study we have investigated the pathway of epitope delivery. The peptides used contained the epitope either located at the C terminus or with a C-terminal extension. Pretreatment of cells with cholesterol-disrupting agents blocked transport of EtxB conjugates to the Golgi/endoplasmic reticulum, but did not affect EtxB-mediated MHC class I presentation. Under these conditions, EtxB conjugates entered EEA1-positive early endosomes where peptides were cleaved and translocated into the cytosol. Endosome acidification was required for epitope presentation. Purified 20 S immunoproteasomes were able to generate the epitope from peptides in vitro, but 26 S proteasomes were not. Only presentation from the C-terminal extended peptide was proteasome-dependent in cells, and this was found to be significantly slower than presentation from peptides with the epitope at the C terminus. These results implicate the proteasome in the generation of the correct C terminus of the epitope and are consistent with proteasome-independent N-terminal trimming. Epitope presentation was blocked in a TAP-deficient cell line, providing further evidence that conjugated peptides enter the cytosol as well as demonstrating a requirement for the peptide transporter. Our findings demonstrate the utility of EtxB-mediated peptide delivery for rapid and efficient loading of MHC class I epitopes in several different cell types. Conjugated peptides are released from early endosomes into the cytosol where they gain access to proteasomes and TAP in the "classical" pathway of class I presentation.

Characterization of the Acetaminophen-Induced Degradation of Cytochrome P450-3A4 and the Proteolytic Pathway

It has been shown that large doses of acetaminophen can result in increased degradation of the hepatic cytochrome P450 (CYP) enzymes in vivo; however, the proteolytic pathways have not been identified. We found that incubating transfected HepG2 cells that express CYP3A4 or a reconstituted microsomal model containing human liver microsomes and cytosol, high concentrations of acetaminophen could induce a dose- and time-dependent degradation of CYP3A4. In the microsomal model the degradation could be blocked and augmented by the presence of catalase and superoxide dismutase, respectively. Tocopherol could also protect against the acetaminophen-induced degradation. However, lipid peroxidation assays showed no significant increases in lipid peroxidation products nor was there any protection by propyl gallate. Protease and proteasome inhibitors showed that the proteolytic process was mainly (85%) mediated by the lysosomal pathway, whereas a minor portion (15%) of the degradation was mediated by the proteasomal pathway. Both pepstatin A and anti-cathepsin D neutralizing antibody decreased acetaminophen-induced degradation of CYP3A4 in microsomal model systems. Pepstatin A also blocked the acetaminophen-induced degradation of the CYP3A4 in a transfected HepG2 cell line. Incubating the 3A4 cells in the presence of acetaminophen also increased cathepsin D content and activity. The lysosomal pathway, mainly mediated by cathepsin D, appears to be the major proteolytic pathway involved in the degradation of the P450 enzymes induced by toxic doses of acetaminophen.

Biochemical entities that influence membrane-associated TNF RII (80-kDa) and IL-1 RI (80-kDa) complex expression and receptor fragment production in adherent vascular endothelium

The research aim of the present investigation was to identify leukocyte enzyme-proteases that have the capacity to biochemically recruit the passive participation of vascular endothelium in cytokine receptor 'shedding' phenomenon involving membrane-associated TNF RII (80-kDa) and IL-1 RI (80-kDa) complexes. Achieving this research objective involved the design of a laboratory approach that delineated to what extent enzyme-proteases released by activated macrophages directly interact with, and liberate soluble fragments of membrane-associated cytokine receptor complexes. Results from this segment of the investigation revealed that cathepsin-D, a leukocyte carboxyl/aspartate protease, altered the integrity and generated soluble fragments of TNF RII (80-kDa) and IL-1 RI (80-kDa) receptor complexes expressed by vascular endothelium. Furthermore, laboratory findings also suggested that cathepsin-D possessed the ability to variably deplete biologically functional membrane-associated TNF RII (80-kDa) and IL-1 RI (80-kDa) complexes. Complementary investigations isolated a carboxyl/aspartate protease from activated macrophages utilizing pepstatin-A affinity chromatography. Exposure of vascular endothelium to pepstatin-A binding proteins resulted in a detectable depletion of membrane-associated TNF RII (80-kDa) and IL-1 RI (80-kDa) in addition to the generation of soluble receptor fragments. Analysis of macrophage pepstatin-A binding proteins by SDS-PAGE identified a primary fraction with a molecular mass of 47-52-kDa that closely correlated with the known molecular mass of leukocyte cathepsin-D. Evaluation of macrophage pepstatin-A binding-protein fractions by non-denaturing Hb-PAGE detected a lucent proteolytic band at 47-52-kDa compatible with the known molecular mass of leukocyte cathepsin-D. Macrophage pepstatin-A binding proteins also hydrolyzed a synthetic enzyme-specific substrate that selectively recognizes cathepsin-D biochemical activity. In conclusion, the leukocyte carboxyl/aspartate protease, cathepsin-D can biochemically alter the integrity and generate soluble fragments of membrane-associated TNF RII (80-kDa) and IL-1 RI (80-kDa) receptor complexes expressed by vascular endothelium. The relevance of this concept is in part based on investigations that have discovered that genetic 'knock-out' mice incapable of expressing IL-1 RI (80-kDa) or TNF RI (55-kDa) receptor complexes are highly resistant to developing the pathophysiological alterations classically associated with conditions of endotoxic-shock.

A history of pepsin and related enzymes

Studies on gastric digestion during 1820-1840 led to the discovery of pepsin as the agent which, in the presence of stomach acid, causes the dissolution of nutrients such as meat or coagulated egg white. Soon afterward it was shown that these protein nutrients were cleaved by pepsin to diffusible products named peptones. Efforts to isolate and purify pepsin were spurred by its widespread adoption for the treatment of digestive disorders, and highly active preparations were available by the end of the nineteenth century. There was uncertainty, however, as to the chemical nature of pepsin, for some preparations exhibited the properties of proteins while other preparations failed to do so. The question was not settled until after 1930, when Northrop crystallized swine pepsin and provided convincing evidence for its identity as a protein. The availability of this purified pepsin during the 1930s also led to the discovery of the first synthetic peptide substrates for pepsin, thus providing needed evidence for the peptide structure of native proteins, a matter of debate at that time. After 1945, with the introduction of new separation methods, notably chromatography and electrophoresis, and the availability of specific proteinases, the amino acid sequences of many proteins, including pepsin and its precursor pepsinogen, were determined. Moreover, treatment of pepsin with chemical reagents indicated the participation in the catalytic mechanism of two aspartyl units widely separated in the linear sequence. Studies on the kinetics of pepsin action on long chain synthetic peptides suggested that the catalytic site was an extended structure. Similar properties were found for other "aspartyl proteinases," such as chymosin (used in cheese making), some intracellular proteinases (cathepsins), and plant proteinases. After 1975, the three-dimensional structures of pepsin and many of its relatives were determined by means of x-ray diffraction techniques, greatly extending our insight into the mechanism of the catalytic action of these enzymes. That knowledge has led to the design of new inhibitors of aspartyl proteinases, which are participants in the maturation of human immunodeficiency virus and in the generation of Alzheimer's disease.

Hemoglobin-degrading, aspartic proteases of blood-feeding parasites: substrate specificity revealed by homology models

Blood-feeding parasites, including schistosomes, hookworms, and malaria parasites, employ aspartic proteases to make initial or early cleavages in ingested host hemoglobin. To better understand the substrate affinity of these aspartic proteases, sequences were aligned with and/or three-dimensional, molecular models were constructed of the cathepsin D-like aspartic proteases of schistosomes and hookworms and of plasmepsins of Plasmodium falciparum and Plasmodium vivax, using the structure of human cathepsin D bound to the inhibitor pepstatin as the template. The catalytic subsites S5 through S4' were determined for the modeled parasite proteases. Subsequently, the crystal structure of mouse renin complexed with the nonapeptidyl inhibitor t-butyl-CO-His-Pro-Phe-His-Leu [CHOHCH(2)]Leu-Tyr-Tyr-Ser- NH(2) (CH-66) was used to build homology models of the hemoglobin-degrading peptidases docked with a series of octapeptide substrates. The modeled octapeptides included representative sites in hemoglobin known to be cleaved by both Schistosoma japonicum cathepsin D and human cathepsin D, as well as sites cleaved by one but not the other of these enzymes. The peptidase-octapeptide substrate models revealed that differences in cleavage sites were generally attributable to the influence of a single amino acid change among the P5 to P4' residues that would either enhance or diminish the enzymatic affinity. The difference in cleavage sites appeared to be more profound than might be expected from sequence differences in the enzymes and hemoglobins. The findings support the notion that selective inhibitors of the hemoglobin-degrading peptidases of blood-feeding parasites at large could be developed as novel anti-parasitic agents.

Biochemical mechanisms that interact with membrane-associated IL-1 RII (60-kDa decoy) receptors in populations of adherent macrophages and vascular endothelium

The aim of this investigation was to identify the potential biochemical mechanisms that alter the integrity of membrane-associated IL-1 RII (decoy) receptor complexes expressed by populations of adherent macrophages and vascular endothelium. The initial research strategy utilized to achieve this objective involved delineating the ability of macrophage activation or exposure of macrophages and vascular endothelium to a spectrum of enzyme proteases to influence the expression of membrane-associated IL-1 RII (decoy) or generate soluble fragments of this receptor complex. Results from these investigations revealed that stimulated macrophages displayed proportional increases in both the expression of membrane-associated IL-1 RII (decoy) and release of soluble receptor fragments. Exposure of macrophages and vascular endothelium to the reference proteases discovered the ability of cathepsin-D to biochemically deplete membrane-associated IL-1 RII (decoy) in addition to generating soluble fragments of this receptor complex. Complementary investigations isolated a carboxyl/aspartate protease from activated macrophages utilizing pepstatin-A affinity chromatography. Exposure of vascular endothelium to pepstatin-A binding proteins resulted in a detectable depletion of membrane-associated IL-1 RII (decoy) and generation of soluble receptor fragments. Evaluation of pepstatin-A binding proteins by SDS-PAGE identified a primary protein fraction with a molecular mass of 47-52 kDa that closely correlates with the known molecular size of leukocyte cathepsin-D fractions. Macrophage pepstatin-A binding protein fractions evaluated by nondenaturing haemoglobin-substrate PAGE (Hb-PAGE) analysis detected a lucent proteolytic band at 47-52 kDa. Macrophage pepstatin-A binding proteins also hydrolyzed a synthetic enzyme-specific substrate that selectively recognizes cathepsin-D biochemical activity. In conclusion, the leukocyte carboxyl/aspartate protease cathepsin-D can biochemically alter the integrity and generate soluble fragments of membrane-associated IL-1 RII (60-kDa decoy) receptor complexes expressed by macrophages and vascular endothelium.

Biochemical alteration of membrane-associated IL-6 RI (80-kDa) in adherent macrophages and vascular endothelium

The potential biochemical mechanisms that mediate the 'shedding' of soluble IL-6 RI (80-kDa) receptor fragments in populations of adherent macrophages were explored. Stimulated macrophages displayed proportional increases in both the expression of membrane-associated IL-6 RI (80-kDa) and the release of soluble receptor fragments. The use of protease inhibitors implicated thiol/cysteine and carboxyl/aspartate proteases in this process. Cathepsin-D depleted membrane-associated IL-6 RI (80-kDa) complexes and generated soluble receptor fragments. A carboxyl/aspartate protease from activated macrophages isolated utilizing pepstatin-A affinity chromatography, was also found to affect membrane-associated IL-6 RI (80-kDa) complexes and generate soluble receptor fragments. Most likely, this fraction corresponded to cathepsin-D based upon its origin, pepstatin-A binding avidity, Hb-PAGE zymography, and hydrolysis of an enzyme-specific substrate. We conclude that cathepsin-D can generate soluble fragments of IL-6 RI (80-kDa) expressed by both macrophages and vascular endothelium.

A new purification method for overproduced proteins sensitive to endogenous proteases

Proteolysisis a major problem in purification of overproduced proteins for structural studies. We developed a new method to avoid proteolysis of the products even in cases where popular protease inhibitors do not work effectively. When we cloned FlgF, a flagellar rod protein, from Salmonella typhimurium and overproduced it in Escherichia coli, FlgF was highly susceptible to cleavage by endogenous proteases after cell disruption even in the presence of various protease inhibitors. However, FlgF was not digested when the cells were disrupted in the presence of urea, which allowed us to develop the following new purification procedure. After cell disruption in the presence of urea and removal of the cell debris, the supernatant was passed through tandem-connected cation- and anion-exchange columns. Proteases were trapped in the cation-exchange column, and protease-free FlgF was eluted from the disconnected anion-exchange column. This gave a stable full-length product suitable for crystallization trials. The key procedures are cell disruption in the presence of urea and linked ion-exchange chromatography to quickly remove proteases as well as urea. This fast and simple method can be applied to purification of other overproduced proteins that are very sensitive to proteolysis.

Mass spectrometry and immobilized enzymes for the screening of inhibitor libraries

A technique has been developed to rapidly screen enzyme inhibitor candidates from complex mixtures, such as those created by combinatorial synthesis. Inhibitor libraries are screened by using immobilized enzyme technologies and electrospray ionization ion cyclotron resonance mass spectrometry. The library mixture is first sprayed into the mass spectrometer, and compounds are identified. The library is subsequently incubated with the immobilized enzyme of interest under the correct conditions (buffer, pH, temperature) by using an excess of enzyme to ensure a surplus of sites for ligand binding. The immobilized enzyme/inhibitor mixture is centrifuged, and an aliquot of supernatant is again analyzed by electrospray ionization mass spectrometry. Potential inhibitors are quickly identified by comparison of the spectra before and after incubation with the immobilized enzyme. Non-inhibitors show no change in ion intensity after incubation, whereas weak inhibitors exhibit a visible decrease in ion abundance. Once inhibitor candidates have been identified, the library is reinjected into the mass spectrometer, and tandem mass spectrometry is used to determine the structure of the inhibitor candidates as needed. This method has been successfully demonstrated by identifying inhibitors of the enzymes pepsin and glutathione S-transferase from a 19- and 17-component library, respectively. It is further shown that the immobilized enzyme can be recycled and reused for continuous screening of additional new libraries without adding additional enzyme.

Localization of pepstatin's inhibitory action during Fc-mediated antibody internalization: possible implications for antibody-mediated viral transmission

Antibody internalization via Fc receptors is an important cellular mechanism, possibly facilitating the entry of antigenic peptides or viral particles into cells when specific antibodies are present at the periphery. Using an experimental model of trophoblast cells, we have shown that anti-p21(ras) monoclonal antibodies can use IFN-gamma-induced surface Fcgamma receptors to enter the cell. This entry of anti-p21(ras) antibodies ultimately inhibits IFN-gamma-mediated class II antigen induction. Since there may be obvious and inevitable harmful aspects of this mechanism, during which Fc-mediated viral particle or autoantigen transport may occur, we concentrated efforts on defining a potent inhibitor able to eliminate such uptake. The results presented here show that the protease inhibitor pepstatin A efficiently inhibits Fcgamma receptor induction by IFN-gamma and also blocks the endocytic pathway followed by an antibody when it enters the cell at the level of early endosomal compartments. We thus postulate that the use of pepstatin A, because of its inhibition of autoantigen presentation or viral transmission, including that of HIV, may find important applications in therapeutic protocols.

Analysis of the endocytic pathway upon intracellular transport of IgG molecules through Fc receptors

The uniformly distributed Fc receptors (FcRs) on the surface of many cell types are involved in a variety of immune reactions by non-specifically facilitating the entry of antigen-specific IgG molecules to the cell. Such reactions may be beneficial to the organism when foreign antigens are involved, or harmful in cases of self antigens and viruses. In order to avoid the IgG-mediated self antigen presentation or viral infection in autoimmunity and viral attack respectively, we attempt in this study to inhibit the intracellular transport of antibodies. This blockage, however, implies: efficacy of inhibition, inability of de novo exocytosis of the internalised antibody and finally maintenance of normal cell growth and morphology. We thus concentrate our interest on the endocytic pathway followed by a neutralising antibody in murine trophoblast cells where we try to inhibit antibody intracellular transport by various agents according to the criteria set above. In our model-system, IFN-gamma, upon induction of FcRs, facilitates endocytosis of the anti-p21ras antibody which blocks in turn the IFN-gamma-induced surface class II major histocompatibility complex (MHC) expression. Using various intracellular transport inhibitors, we study the required conditions by which these compounds cancel the inhibitory action of anti-p21ras and allow induction of class II MHC molecules by IFN-gamma. The effectiveness of the inhibitors in a ranking order is shown as following: monodansyl cadaverine > didansyl cadaverine > pepstatin A > leupeptin > NH4Cl > brefeldin A > ZPCK > TPCK. From these inhibitors, only brefeldin A, leupeptin, pepstatin and ZPCK do not allow exocytosis of the antibody in the culture medium and only didansyl cadaverine, pepstatin and leupeptin maintain cell viability and morphology. However, by sequential elimination based on this study's established criteria, only pepstatin A and leupeptin are shown to be effective inhibitors to specific antibody intracellular transport, protecting also the cell's viability and physiology.

Analysis of cathepsin D forms and their clinical implications in human prostate cancer

PURPOSE

To assess cathepsin D (Cat.D) status in the prostate, we analyzed the different Cat.D forms in human prostate tissues using Western immunoblots.

MATERIALS AND METHODS

Cell extracts were prepared from prostate tissues (n = 42) obtained from radical prostatectomy, adopting the tissue homogenization method. Expression of the different Cat.D forms was analyzed using Western blots. The catalytic activity of Cat.D was assayed by acid treatment, in which cell extracts were incubated in acidic buffer (pH 3 to 4) at 37C for 1 hour.

RESULTS

Pathologically confirmed normal (NML), benign prostatic hyperplasia (BPH) and cancer (CAP) specimens all expressed Cat.D, but as two distinct forms. Both NML and BPH predominantly expressed an inactive procathepsin D (Pro.Cat.D), while CAP notably exhibited an active mature Cat.D. The assessment of Cat.D activity, using PSA (prostate specific antigen) as a physiological substrate, showed that such activity was consistently higher in CAP than in NML/BPH specimens. Further studies revealed that the mode of Cat.D activation in CAP specimens appeared to be primarily due to acid-induced autoproteolysis (self-degradation) of mature Cat.D.

CONCLUSION

This study demonstrates that expression and activity of Cat.D varies among prostate specimens. A greater expression of mature Cat.D with a higher catalytic activity in CAP specimens is the most notable difference from NML/BPH. Therefore, the differential expression/activity of Cat.D forms may be a useful indicator for assessing prostate cancer status.

Hydrolysis of androgen receptor by cathepsin D: its biological significance in human prostate cancer

OBJECTIVE

To elicit the biological role of a lysosomal protease, cathepsin D (CatD) in prostate cancer, by investigating its regulatory effect on the androgen receptor (AR) using human prostate cancer LNCaP cells and prostate tissue specimens.

MATERIALS AND METHODS

Cell extracts were prepared from LNCaP or prostate specimens by cell lysis and tissue homogenization. Proteolytic assays were performed by incubating these extracts in acidic buffer (pH 3-4) at 37 degrees C. The resulting effects on AR and CatD were then analysed using Western immunoblots.

RESULTS

The Western blots showed that AR was virtually hydrolysed with acid treatment, because endogenous CatD was activated; this activation only occurred at pH 3.2-3.5, but no specific acid appeared to be required. Further analyses suggested that CatD activation could be attributed to acid-induced autoproteolysis of mature CatD. Similar assays were also performed on prostate tissues, including normal and malignant specimens. These studies revealed that CatD-mediated AR hydrolysis was observed only in cancer specimens, while no such hydrolysis occurred in normal specimens.

CONCLUSION

Endogenous CatD can hydrolyse AR, thereby possibly modulating AR function/metabolism in LNCaP cells, and in cancer specimens. CatD activity also appears to differ significantly between normal and malignant tissue. Thus, CatD may play a pivotal role as a growth modulator in androgen-dependent prostate cancer.

Application of polymannosylated cystatin to surimi from roe-herring to prevent gel weakening

A recombinant glycosylated cystatin with a polymannosyl chain was added to roe-herring surimi for preventing gel weakening due to autolysis during cooking. Proteolysis of myosin heavy chain in the surimi was effectively suppressed while cooking at 90 degrees C for 20 min after preincubation at 40 degrees C for 30 min. The glycosylation of cystatin improved the stability against heating as well as proteolysis by cathepsin D. This process markedly improved the texture of the cooked surimi gel with gel strength 2.5 times that of unglycosylated control cystatin.

Unstable proteins: how to subject them to chromatographic separations for purification procedures

The chromatographic separation of an unstable protein is often a challenge to the scientist working in the field of life sciences. Especially for the purification of sensitive enzymes, making use of conventional chromatographic techniques is difficult and frequently results in a complete loss of biological activity of the target protein. This report summarizes some general strategies that may help to keep unstable proteins in their native conformation during the rather harsh conditions of a purification procedure. In this context, a recently developed hollow fiber membrane module, suitable for performing on-line dialysis, is introduced and examples of its application to liquid column chromatography are given. Many innovative separation techniques, characterized by dramatic improvements in both performance and separation time, have recently been developed. Since the chromatographic separation of unstable proteins requires the use of modern state-of-the-art equipment and technology, emphasis is given to newly developed separation techniques such as expanded bed adsorption, perfusion chromatography, protein free flow electrophoresis and the use of tentacle gels. In addition, examples of recently published purifications of unstable proteins are discussed with respect to strategies ensuring the preservation of the native protein structure during chromatographic separation.

Renin inhibition: a novel therapy for cardiovascular disease

The renin-angiotensin system (RAS) is a major contributor in the regulation of blood pressure, and pharmacologic manipulation of this system has resulted in a beneficial class of therapeutic agents, which include angiotensin-converting enzyme (ACE) inhibitors. However, ACE inhibitors are not specific for RAS, and in addition, they can affect bradykinin and prostaglandin, which can also cause changes in vascular tone. Under development are renin inhibitors that are specific for angiotensinogen and act at the initial, rate-determining step of the RAS cascade. The various pharmacologic approaches to renin inhibition include specific renin antibodies, synthetic derivatives of the prosegment of renin precursor, pepstatin analogs, and angiotensinogen analogs. The last approach is the most promising for patient therapy. Multiple studies have shown the effectiveness of the renin inhibitors in both primates and human beings. Further research is now directed toward the development of an agent with good oral bioavailability for patient treatment and as a biologic probe for helping to understand the role of the RAS in control of blood pressure and blood volume.