Mode of inhibition of acid proteases by pepstatin

Aspartic proteinases in Antarctic fish

The present review surveys several recent studies of the aspartic proteinases from Antarctic Notothenioidei, a dominating fish group that has developed a number of adjustments at the molecular level to maintain metabolic function at low temperatures. Given the unique peculiarities of the Antarctic environment, studying the features of Antarctic aspartic proteinases could provide new insights into the role of these proteins in fish physiology. We describe here: (1) the biochemical properties of a cathepsin D purified from the liver of the hemoglobinless icefish Chionodraco hamatus; (2) the biochemical characterization of Trematomus bernacchii pepsins variants A1 and A2 obtained by heterologous expression in bacteria; and (3) the identification of two closely related, novel aspartic proteinases from the liver of the two Antarctic fish species mentioned above. Overall, the results show that Notothenioidei aspartic proteinases display a number of characteristics that are remarkably different from those of mammalian aspartic proteinases, including high turnover number or high catalytic efficiency. We have named the newly identified aspartic proteinases "Nothepsins" and classified them relative to aspartic proteinases from other species.

Peptide inhibition of HIV-1: current status and future potential

More than 2 decades of intensive research has focused on defining replication mechanisms of HIV type 1 (HIV-1), the etiologic agent of AIDS. The delineation of strategies for combating this viral infection has yielded many innovative approaches toward this end. HIV-1 is a lentivirus in the family retroviridae that is relatively small with regard to both structure and genome size, having a diploid RNA genome of approximately 9 kb, with only three major genes and several gene products resulting from alternate splicing and translational frameshifting. Most marketed drugs for treating AIDS are inhibitors of HIV-1 reverse transcriptase or protease enzymes, but new targets include the integrase enzyme, cell surface interactions that facilitate viral entry, and also virus particle maturation and assembly. The emergence of drug-resistant variants of HIV-1 has been the main impediment to successful treatment of AIDS. Thus, there is a pressing need to develop novel treatment strategies targeting multiple stages of the virus life-cycle. Research efforts aimed at developing successful means for combating HIV-1 infection have included development of peptide inhibitors of HIV-1. This article summarizes past and current endeavors in the development of peptides that inhibit replication of HIV-1 and the role of peptide inhibitors in the search for new anti-HIV drugs.

beta-Secretase as a therapeutic target for Alzheimer's disease

beta-Secretase (memapsin 2, BACE1) is an attractive target for the development of inhibitor drugs to treat Alzheimer's disease (AD). Not only does this protease function at the first step in the pathway leading to the production of amyloid-beta (Abeta), its gene deletion produces only mild phenotypes. In addition, beta-secretase is an aspartic protease whose mechanism and inhibition are well known. The development of beta-secretase inhibitors, actively pursued over the last seven years, has been slow, due to the difficulty in combining the required properties in a single inhibitor molecule. Steady progress in this field, however, has brought about inhibitors that contain many targeted characteristics. In this review, we describe the strategy of structure-based inhibitor evolution in the development of beta-secretase inhibitor drug. The current status of the field offers grounds for some optimism, in that beta-secretase inhibitors have been shown to reduce brain Abeta and to rescue the cognitive decline in transgenic AD mice, and an orally available beta-secretase inhibitor drug candidate is in clinical trial. With this knowledge base, it seems reasonable to expect that more drug candidates will be tested in human, and then successful disease-modifying drugs may ultimately emerge from this target.

Establishing objective detection limits for the pepsin digestion assay used in the assessment of genetically modified foods

RATIONALE

Guidelines for assessing the potential allergenicity of genetically modified (GM) organisms recommend testing the digestibility of the introduced protein by pepsin. Previous studies detailed the digestion procedure but have not described a simple objective measurement of the extent of digestion nor evaluated the impact of variation in pepsin activity.

METHODS

Samples of eight proteins were digested by pepsin at pH 1.2 and 2.0 using standard conditions (10,000 U of pepsin activity per mg test protein) as well as 5000 and 20,000 units per mg of test protein. An independent digestion assay of hemoglobin was used to verify pepsin activity for each assay. Digestion was stopped in timed samples between 0.5 and 60 min. Digestion samples and undigested protein (10% and 100%) were separated by SDS-PAGE. Residual stained protein bands were measured by image analysis.

RESULTS

The differences in pH and pepsin concentration only had minor effects on digestion of intermediately stable proteins: concanavalin A, ovalbumin, and lysozyme, but not on rapidly digested or stable proteins.

CONCLUSIONS

Verification of pepsin activity and measurement of an objective endpoint of digestion (e.g. (90%) should provide more comparable results for the safety assessment of novel food proteins.

Picomolar detection of protease using peptide/single walled carbon nanotube/gold nanoparticle-modified electrode

Picomolar electrochemical detection of human immunodeficiency virus type-1 protease (HIV-1 PR) using ferrocene (Fc)-pepstatin-modified surfaces has been presented. Gold electrode surface was modified with gold nanoparticles (AuNP) or thiolated single walled carbon nanotubes/gold nanoparticles (SWCNT/AuNP). Thiol-terminated Fc-pepstatin was then self-assembled on such surfaces as confirmed by Raman spectroscopy and scanning electron microscope. The interaction between the Fc-pepstatin-modified substrates and HIV-1 PR was studied by cyclic voltammetry and electrochemical impedance spectroscopy. Both electrode materials showed enhanced electrochemical responses to increasing concentrations of HIV-1 PR with shifting to higher potentials as well as decrease in the overall signal intensity. However, the sensing electrode modified with thiolated SWCNTs/AuNPs showed remarkable detection sensitivity with an estimated detection limit of 0.8 pM.

Human cathepsin D

A literature survey was performed of human cathepsin D gene, cathepsin D biosynthesis, posttranslatory modifications, transport within the cell, substrate specificity and catalytic effect. Methods used to determine the activity and level of this proteinase as well as its role in the biochemistry and pathobiochemistry of cells, tissues and organs were considered.

Interaction of pepsin with aromatic amino acids and their derivatives immobilized to Sepharose

The interaction of porcine pepsin A with immobilized derivatives of aromatic amino acids was investigated. Divinyl sulfone-activated Sepharose was used to immobilize N-acetyl-l-phenylalanine and 3,5-diiodo-l-tyrosine via their free carboxyl groups and l-tyrosine via its amino group. Immobilized l-tyrosine was iodinated after coupling. The optimum conditions for the separation of porcine pepsin A using the prepared affinity carriers were studied and the following parameters were established: enzyme recovery, reproducibility of analyses, capacity and dependence of the elution peak area on the concentration of the loaded enzyme. The ability of the prepared affinity carriers to retain various types of proteins was compared under optimum conditions for porcine pepsin A separation. While immobilized 3,5-diiodo-l-tyrosine and iodinated l-tyrosine-Sepharose adsorbed relatively high amounts of bovine serum albumin and ovalbumin, only negligible amounts of these proteins were adsorbed to immobilized N-acetyl-l-phenylalanine. The behavior of porcine pepsin A was the same as its complex with pepstatin A on the prepared affinity carriers, indicating that the enzyme active site is not involved in the studied interaction.

Purification and characterization of pepsins A1 and A2 from the Antarctic rock cod Trematomus bernacchii

The Antarctic notothenioid Trematomus bernacchii (rock cod) lives at a constant mean temperature of -1.9 degrees C. Gastric digestion under these conditions relies on the proteolytic activity of aspartic proteases such as pepsin. To understand the molecular mechanisms of Antarctic fish pepsins, T. bernacchii pepsins A1 and A2 were cloned, overexpressed in Escherichia coli, purified and characterized with a number of biochemical and biophysical methods. The properties of these two Antarctic isoenzymes were compared to those of porcine pepsin and found to be unique in a number of ways. Fish pepsins were found to be more temperature sensitive, generally less active at lower pH and more sensitive to inhibition by pepstatin than their mesophilic counterparts. The specificity of Antarctic fish pepsins was similar but not identical to that of pig pepsin, probably owing to changes in the sequence of fish enzymes near the active site. Gene duplication of Antarctic rock cod pepsins is the likely mechanism for adaptation to the harsh temperature environment in which these enzymes must function.

Leishmania mexicana: Identification and characterization of an aspartyl proteinase activity

An aspartyl proteinase activity was detected in the soluble fraction (SF) of Leishmania mexicana promastigotes by the use of the synthetic substrate benzoyl-Arg-Gly-Phe-Phe-Leu-4-methoxy-beta-naphthylamide selective for Cathepsin D like aspartyl-proteinases. This peptide was hydrolyzed with an apparent K(m) of 2.3+/-0.3 microM. The classic inhibitor of aspartyl-proteinases, diazo-acetyl-norleucinemethylester (DAN) inhibited the proteolytic activity with an IC(50) of 400 microM. The soluble fraction degraded (in absence of thiol groups) human fibrinogen with a specific activity of 533 U/mg protein. When tested for the ability to inhibit the "in vitro" proliferation of L. mexicana promastigotes, DAN showed concentration dependent anti-proliferative effects with a LD(50) of 466 microM at 48 h, with a significant fall in this value to 22 microM after 72 h. This is the first characterization of an aspartyl-proteinase activity in Leishmania, calling for further studies directed towards the physiologic role of these enzymes in the parasite. The anti-proliferative effect of its inhibition makes this enzyme a putative new target for the development of leishmanicidal drugs.

Affinity chromatography of porcine pepsin A using quinolin-8-ol as ligand

Stationary phase containing quinolin-8-ol immobilized on macroporous methacrylate support for the affinity chromatography of porcine pepsin A is described. Optimized chromatographic conditions for separation of porcine pepsin A on this stationary phase were found investigating the influence of pH, concentration, ionic strength and chemical composition of the used mobile phases. The stationary phase shows a good reproducibility of chromatographic analyses (relative standard deviation, +/-2%), a high recovery (ca. 93%) and a satisfactory capacity (13 mg pepsin A/1 mL stationary phase) for porcine pepsin A. The obtained findings confirm the applicability of affinity chromatography on the stationary phase with immobilized quinolin-8-ol to the isolation and determination of porcine pepsin A.

Inhibition of 1,4-beta-D-xylan xylanohydrolase by the specific aspartic protease inhibitor pepstatin: probing the two-step inhibition mechanism

This is the first report that describes the inhibition mechanism of xylanase from Thermomonospora sp. by pepstatin A, a specific inhibitor toward aspartic proteases. The kinetic analysis revealed competitive inhibition of xylanase by pepstatin A with an IC50 value 3.6 +/- 0.5 microm. The progress curves were time-depended, consistent with a two-step slow tight binding inhibition. The inhibition followed a rapid equilibrium step to form a reversible enzyme-inhibitor complex (EI), which isomerizes to the second enzyme-inhibitor complex (EI*), which dissociated at a very slow rate. The rate constants determined for the isomerization of EI to EI* and the dissociation of EI* were 15 +/- 1 x 10(-5) and 3.0 +/- 1 x 10(-8) s(-1), respectively. The Ki value for the formation of EI complex was 1.5 +/- 0.5 microm, whereas the overall inhibition constant Ki* was 28.0 +/- 1 nm. The conformational changes induced in Xyl I by pepstatin A were monitored by fluorescence spectroscopy, and the rate constants derived were in agreement with the kinetic data. Thus, the conformational alterations were correlated to the isomerization of EI to EI*. Pepstatin A binds to the active site of the enzyme and disturbs the native interaction between the histidine and lysine, as demonstrated by the abolished isoindole fluorescence of o-phthalaldehyde-labeled xylanase. Our results revealed that the inactivation of xylanase 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, and a model depicting the probable interaction between pepstatin A with xylanase has been proposed.

Aspartic proteinase members secreted by the ruminant placenta: specificity of three radioimmunoassay systems for the measurement of pregnancy-associated glycoproteins

Pregnancy-associated glycoproteins (PAGs) isolated from the placenta of various ruminant species are enzymatically inactive members of the aspartic proteinase family. The measurement of these proteins in the maternal blood can be a good indicator of the presence of a live embryo. As certain aspartic proteinases are present in biological fluids in physiological and pathological conditions at various concentrations, it was necessary to determine the specificity of three radioimmunoassay (RIA) systems currently used for the detection of PAG molecules. Commercially available members of the aspartic proteinase family like pepsinogen, pepsin, chymosin, rennet, cathepsin D and renin were tested in a wide concentration range (10 ng/ml - 1 mg/ml). Pepsinogen cross-reacted in RIA 1, RIA 2 and RIA 3 over 1 mg/ml, 50 microg/ml and 500 microg/ml concentrations, respectively. In the presence of pepsin, cross-reaction was observed in RIA 1, RIA 2 and RIA 3 over 1 mg/ml, 500 microg/ml and 1 mg/ml concentrations, respectively. Chymosin and rennet could cross-react in RIA 2 and RIA 3, while renin and cathepsin D did not decrease the binding of the tracer to antisera more, than that of the minimal detection limit. As the plasma/serum concentrations of the examined aspartic proteinases reported in the literature were outside the concentration range where cross-reaction was observed, it can be concluded that these RIA systems were specific for the detection of PAGs in biological fluids.

Novel inhibition of porcine pepsin by a substituted piperidine. Preference for one of the enzyme conformers

Pepsin inhibition by 3-alkoxy-4-arylpiperidine (substituted piperidine; (3R,4R)-3-(4-bromobenzyloxy)-4-[4-(2-naphthalen-1-yl-2-oxo-ethoxy)phenyl]piperidine) has been studied using steady-state kinetic and pre-equilibrium binding methods. Data were compared with pepstatin A, a well known competitive inhibitor of pepsin. Steady-state analysis reveals that the substituted piperidine likewise behaves as a competitive inhibitor. Pre-equilibrium binding studies indicate that the substituted piperidine can displace a fluorescently labeled statine inhibitor from the enzyme active site. Simulation of the stopped-flow fluorescence transients provided estimates of the K(d) values of 1.4 +/- 0.2 microm and 39 +/- 2 nm for the piperidine and the fluorescently labeled statine, respectively. The effects of combinations of these two inhibitors resulted in a series of parallel lines when plotted by the method of Yonetani and Theorell (Yonetani, T., and Theorell, H. (1964) Arch. Biochem. Biophys. 106, 234-251), suggesting that the two inhibitors bind in a mutually exclusive fashion to pepsin. Fitting of the entire data set to the appropriate equation yielded an alpha factor of 8 +/- 1. The magnitude of this factor ( infinity > alpha > 1) can be explained by a conformational distinction between the enzyme species that bind each inhibitor. The effects of pH on the inhibition constants for pepstatin A and the substituted piperidine also suggest that the inhibitors bind to distinct conformational forms of the enzyme. No inhibition by the piperidine was observed at acidic pH, while pepstatin A inhibition is maximal at low pH values. Inhibition by the piperidine was maximal when a group with pK 4.8 +/- 0.2 was deprotonated and another group with pK 5.9 +/- 0.2 was protonated. Most likely these two groups are the catalytic aspartates with perturbed ionization properties as a result of a significant and unique conformational change. Taken together, these data suggest that the enzyme can readily interconvert between two conformers, one capable of binding substrate and pepstatin A and the other capable of binding the substituted piperidine.

An aspartic proteinase expressed in the yolk sac and neonatal stomach of the mouse

A murine aspartic proteinase, described herein, is intermediate in amino acid sequence identity between the placentally produced pregnancy-associated glycoproteins (PAGs) and gastric pepsins. While PAGs are secreted products of placental trophoblast tissue of ungulates and most are not believed to function proteolytically, pepsins are digestive enzymes. The cDNA for this aspartic proteinase was amplified by reverse transcription-polymerase chain reaction from RNA extracted from murine placentas and neonatal stomachs. The open reading frame encoded a 387-amino acid polypeptide with a 15-residue signal sequence. The enzyme most resembled pepsinogen F (a protein identified in the stomachs of neonatal rabbits and rats) and PAG-like proteins cloned from equine and feline placentae. In the stomach, both its mRNA and protein were expressed in gastric chief cells of preweaned neonates. Within the placenta, its mRNA was present in both the parietal and visceral yolk sacs. However, the protein was most prevalent in the visceral yolk sac, with little detectable in the parietal yolk sac. The recombinant protein was expressed in Escherichia coli. This protein was capable of self-activation and exhibited proteolytic activity toward casein. The presence of this enzyme in two organs involved in the selective transcellular transport of proteins suggests that it has specialized digestive functions.

Molecular model for the binary complex of uropepsin and pepstatin

The three-dimensional structure of human uropepsin complexed with pepstatin has been modelled using human pepsin as a template. Uropepsin is an aspartic proteinase from the urine, produced in the form of pepsinogen A in the gastric mucosa. The structure is bilobal, consisting of two predominantly beta-sheet lobes which, as observed in other aspartic proteinases, are related by a pseudo twofold axis. A structural comparison between binary complexes of pepsin:pepstatin and uropepsin:pepstatin is discussed.

Aspartic protease inhibitors: expedient synthesis of 2-substituted statines

[reaction: see text]. General stereocontrolled synthesis of all four (2,3)-stereoisomers of 2-substituted statines is described. The 2,3-syn and 2,3-anti isomers were synthesized via beta-ketoester reduction and aldol reactions, respectively. Peptides containing 2-substituted statines inhibit porcine pepsin with nanomolar IC50 values.

Hodgkin disease: pharmacologic intervention of the CD40-NFκB pathway by a protease inhibitor

The malignant Reed-Sternberg cell of Hodgkin disease is an aberrant B cell that persists in an immunolgically mediated inflammatory infiltrate. Despite its nonproductive immunoglobulin genes, the Reed-Sternberg cell avoids the usual apoptotic fate of defective immune cells through an unknown mechanism. A likely candidate is the surface receptor, CD40, consistently expressed by Reed-Sternberg cells, and the first link in the pathway to NF-κB activation, the central regulator of cytokine production and apoptosis. CD40 signaling in B lymphocytes coordinates the immune response, including immunoglobulin isotype switch and Fas-mediated apoptosis. CD40-induced NF-κB activation is mediated by adapter proteins, the TNF receptor (TNFR)-associated factors (TRAFs), especially TRAFs 2, 3, and 5. Using a Hodgkin cell line, this study demonstrates that CD40 activation of NF-κB is mediated by proteolysis of TRAF3. Results further demonstrate that the pathway can be blocked by treatment with pharmacologic doses of a specific protease inhibitor, pepstatin-A, even in the presence of a mutated NF-κB inhibitor, I-κBα. The stability of TRAF3 regulates CD40/NF-κB–mediated control of the immune response, which is central to the biologic activity of the Reed-Sternberg cell. Prevention of TRAF3 proteolysis may be an entry point for design of novel pharmaceuticals to treat Hodgkin disease and immune system disorders.

Hodgkin disease: pharmacologic intervention of the CD40-NFκB pathway by a protease inhibitor

The malignant Reed-Sternberg cell of Hodgkin disease is an aberrant B cell that persists in an immunolgically mediated inflammatory infiltrate. Despite its nonproductive immunoglobulin genes, the Reed-Sternberg cell avoids the usual apoptotic fate of defective immune cells through an unknown mechanism. A likely candidate is the surface receptor, CD40, consistently expressed by Reed-Sternberg cells, and the first link in the pathway to NF-κB activation, the central regulator of cytokine production and apoptosis. CD40 signaling in B lymphocytes coordinates the immune response, including immunoglobulin isotype switch and Fas-mediated apoptosis. CD40-induced NF-κB activation is mediated by adapter proteins, the TNF receptor (TNFR)-associated factors (TRAFs), especially TRAFs 2, 3, and 5. Using a Hodgkin cell line, this study demonstrates that CD40 activation of NF-κB is mediated by proteolysis of TRAF3. Results further demonstrate that the pathway can be blocked by treatment with pharmacologic doses of a specific protease inhibitor, pepstatin-A, even in the presence of a mutated NF-κB inhibitor, I-κBα. The stability of TRAF3 regulates CD40/NF-κB–mediated control of the immune response, which is central to the biologic activity of the Reed-Sternberg cell. Prevention of TRAF3 proteolysis may be an entry point for design of novel pharmaceuticals to treat Hodgkin disease and immune system disorders.

Modification of the substrate specificity of porcine pepsin for the enzymatic production of bovine hide gelatin

The substrate specificity of porcine pepsin has been altered by site-directed mutagenesis in an attempt to selectively cleave bovine hide collagen at only a few sites, similar to cathepsin D, for the production of high quality gelatin. Kinetic parameters were determined using chromogenic peptide substrates based on the sequence Lys-Pro-Xaa-Yaa-Phe*Nph-Arg-Leu (where Xaa is Ile or Pro, Yaa is Glu. Leu, Gln or Lys, Nph is p-nitrophenylalanine, and * is the site of cleavage). Substitution of Thr222 and Glu287 within the S2 subsite of pepsin by Val and Met, respectively, produced a double mutant with a two- to fourfold higher kcat/Km, compared with wild-type pepsin, for the chromogenic peptides with residues Leu, Gln, and Glu at position P2 (Yaa). The results suggest that the functional group of the P2 side chain may be exposed to solvent, while the aliphatic portion interacts with hydrophobic residues comprising S2. Wild-type pepsin cleaved a peptide corresponding to the carboxy-terminal telopeptide region of bovine type I collagen alpha1 chain, SGGYDLSFLPQPPQE, predominantly at three sites (Asp-Leu, Leu-Ser, and Phe-Leu) and at a significantly lower rate at Ser-Phe. However, Thr222Val/Glu287Met cleaved site Ser-Phe at a rate 20-fold higher than the wild-type. Significantly, enzymes containing the double substitution Phe111Thr/Leu112Phe cleaved this peptide predominantly at one site Leu-Ser (similar to cathepsin D) and at a rate 23-fold higher than the wild-type. These mutants can potentially enhance the rate of solubilization of bovine hide collagen under conditions mild enough to maintain the triple helix structure and hence minimize the rate of subsequent denaturation and proteolytic cleavage.

A heme-binding aspartic proteinase from the eggs of the hard tick Boophilus microplus

An aspartic proteinase that binds heme with a 1:1 stoichiometry was isolated and cloned from the eggs of the cattle tick Boophilus microplus. This proteinase, herein named THAP (tick heme-binding aspartic proteinase) showed pepstatin-sensitive hydrolytic activity against several peptide and protein substrates. Although hemoglobin was a good substrate for THAP, low proteolytic activity was observed against globin devoid of the heme prosthetic group. Hydrolysis of globin by THAP increased as increasing amounts of heme were added to globin, with maximum activation at a heme-to-globin 1:1 ratio. Further additions of heme to the reaction medium inhibited proteolysis, back to a level similar to that observed against globin alone. The addition of heme did not change THAP activity toward a synthetic peptide or against ribonuclease, a non-hemeprotein substrate. The major storage protein of tick eggs, vitellin (VT), the probable physiological substrate of THAP, is a hemeprotein. Hydrolysis of VT by THAP was also inhibited by the addition of heme to the incubation media. Taken together, our results suggest that THAP uses heme bound to VT as a docking site to increase specificity and regulate VT degradation according to heme availability.

Aspartyl proteases in Caenorhabditis elegans. Isolation, identification and characterization by a combined use of affinity chromatography, two-dimensional gel electrophoresis, microsequencing and databank analysis

Crude homogenates of the nematode Caenorhabditis elegans exhibit maximal proteolytic activity under acidic pH conditions. About 90% of this activity is inhibited by the oligopeptide pepstatin, which specifically inhibits the activity of aspartyl proteases such as pepsin, cathepsins D and E or renin. We have purified enzymes responsible for this proteolytic activity by a single-step affinity chromatography on pepstatin-agarose. Analysis of the purified fraction by 1D SDS gel electrophoresis revealed six bands ranging from 35 to 52 kDa. After electrotransfer to poly(vinylidene difluoride) membranes, all bands were successfully subjected to N-terminal microsequencing. On 2D gels, the purified protein bands split into 19 spots which, after renewed microsequencing, were identified as isoelectric variants of the six proteins already described. The N-termini obtained for these proteins could be correlated to genomic DNA sequences determined in the course of the C. elegans genome sequencing project. All these sequences were predicted to code for expressed proteins as collected in the WORMPEP database. Five of the six coding sequences identified in this study were found to contain the typical active-site consensus sequence of aspartyl proteases and displayed an overall amino acid identity between 25 and 66% as compared to aspartyl proteases from other organisms. In addition to the five aspartyl proteases detected at the protein level, we have identified the coding sequences for seven other enzymes of this protease family by a similarity search in the genomic DNA of C. elegans which has recently been completely sequenced.

Processing, activity, and inhibition of recombinant cyprosin, an aspartic proteinase from cardoon (Cynara cardunculus)

The cDNA encoding the precursor of an aspartic proteinase from the flowers of the cardoon, Cynara cardunculus, was expressed in Pichia pastoris, and the recombinant, mature cyprosin that accumulated in the culture medium was purified and characterized. The resultant mixture of microheterogeneous forms was shown to consist of glycosylated heavy chains (34 or 32 kDa) plus associated light chains with molecular weights in the region of 14,000-18,000, resulting from excision of most, but not all, of the 104 residues contributed by the unique region known as the plant specific insert. SDS-polyacrylamide gel electrophoresis under non-reducing conditions indicated that disulfide bonding held the heavy and light chains together in the heterodimeric enzyme forms. In contrast, when a construct was expressed in which the nucleotides encoding the 104 residues of the plant specific insert were deleted, the inactive, unprocessed precursor form (procyprosin) accumulated, indicating that the plant-specific insert has a role in ensuring that the nascent polypeptide is folded properly and rendered capable of being activated to generate mature, active proteinase. Kinetic parameters were derived for the hydrolysis of a synthetic peptide substrate by wild-type, recombinant cyprosin at a variety of pH and temperature values and the subsite requirements of the enzyme were mapped using a systematic series of synthetic inhibitors. The significance is discussed of the susceptibility of cyprosin to inhibitors of human immunodeficiency virus proteinase and particularly of renin, some of which were found to have subnanomolar potencies against the plant enzyme.

Altered adherence in strains of Candida albicans harbouring null mutations in secreted aspartic proteinase genes

The aspartate proteinase inhibitor pepstatin A has been shown previously to reduce the adherence of Candida albicans yeast cells to human surfaces. This suggests that in addition to their presumed function facilitating tissue penetration, the secreted aspartate proteinases (Saps) of this fungal pathogen may have auxiliary roles as cellular adhesins. We therefore examined the relative adherence of yeast cells of a parental wild-type strain of C. albicans in relation to yeast cells of strains harbouring specific disruptions in various members of the SAP gene family in an otherwise isogenic background. The adhesiveness of delta sap1, delta sap2, delta sap3 null mutants and a triple delta sap 4-6 disruptant was examined on three surfaces--glass coated with poly-L-lysine or a commercial cell-free basement membrane preparation (Matrigel) and on human buccal epithelial cells. Pepstatin A reduced adherence to all surfaces. Adherence of the each of the single SAP null mutants to these three substrates was either reduced or not affected significantly compared to that of the parental strain. The adherence of the delta sap4-6 mutant was reduced on poly-L-lysine and Matrigel, but increased on buccal cells. The results suggest that in addition to a primary enzymatic role, various SAPs may also act singly or synergistically to enhance the adhesiveness to C. albicans cells to certain human tissues.

New renin inhibitors containing novel analogues of statine

Solid-phase methodology has been used to synthesize a series of peptides based on the N-terminal sequence of human angiotensinogen in which statine (Sta) or the novel analogues (3S,4S)-3,4-diamino- or (3R,4S)-3,4-diamino-6-methylheptanoic acid (Ads or R-Ads) and (3S,4S)-4-amino-3-aminomethyl- or (3R,4S)-4-amino-3-aminomethyl-6-methylheptanoic acid (Amd or R-Amd) replace either residue 10 or both residues 10-11 at the P1-P1' cleavage site. The synthesis of these novel analogues of statine together with biological results on the inhibition of human and rat renin by peptides derived from them is reported. The absolute stereochemistry of the (3S,4S) Ads was determined by an X-ray crystallographic analysis of its N gamma-Boc, B beta-Z, R(+)-1-methyl benzamide derivative. Peptide Boc-His-Pro-Phe-His-Sta-Val-Ile-His-NH2 (VI) is the best inhibitor of human renin containing Sta at position 10. However, peptides containing Ads and Amd gave better rat renin inhibitors than the corresponding Sta-containing peptides. Peptides Boc-His-Pro-Phe-His-Ads-Val-Ile-His-NH2 (VII) having Ads at position 10 had an IC50 of 12 nM against rat renin. Although Sta has come to be accepted as an isosteric replacement for a dipeptide unit rather than for a single amino acid residue, in our series of inhibitors Sta is more effective when replacing only the amino acid at position 10 in the natural angiotensinogen sequence. None of the peptides gave any effect in vivo in a hypertensive rat model.

Ionization states of the catalytic residues in HIV-1 protease

Chemical synthesis was used to prepare the HIV-1 protease specifically 13C-labelled in the catalytically essential Asp 25 in each monomer. The NMR chemical shift of the 13C-enriched homodimeric enzyme was measured in the presence of the inhibitor pepstatin, a mimic of the tetrahedral intermediate formed in enzyme catalysis. In this complex, the catalytic carboxyls do not titrate in the pH range where the enzyme is active; throughout the range pH 2.5-6.5, one Asp 25 side chain is protonated and the other deprotonated. By contrast, in the absence of inhibitor the two Asp side chains are chemically equivalent and both deprotonated at pH6, the optimum for enzymatic activity. These direct observations of the chemical properties of the catalytic apparatus of the enzyme provide concrete information on which to base the design of improved HIV-1 protease inhibitors.

Current trends in molecular recognition and bioseparation

Molecular recognition guides the selective interaction of macromolecules with each other in essentially all biological processes. Perhaps the most impactful use of biomolecular recognition in separation science has been in affinity chromatography. The results of the last 26 years, since Cuatrecases, Wilchek and Anfinsen first reported the purification of staphylococcal nuclease, have validated the power of biomolecular specificity for purification. This power has stimulated an explosion of solid-phase ligand designs and affinity chromatographic applications. An ongoing case in point is the purification of recombinant proteins, which has been aided by engineering the proteins to contain Affinity-Tag sequences, such as hexa-histidine for metal-chelate separation and epitope sequence for separation by an immobilized monoclonal antibody. Tag technology can be adapted for plate assays and other solid-phase techniques. The advance of affinity chromatography also has stimulated immobilized ligand-based methods to characterize macromolecular recognition, including both chromatographic and optical biosensor methods. And, new methods such as phage display and other diversity library approaches continue to emerge to identify new recognition molecules of potential use as affinity ligands. Overall, it is tantalizing to envision a continued evolution of new affinity technologies which use the selectivity built into biomolecular recognition as a vehicle for purification, analysis, screening and other applications in separation sciences.

Aspartic proteinases--Fourier transform IR studies of the aspartic carboxylic groups in the active site of pepsin

Fourier transform (FTIR) difference spectra of pepsin minus diazoacetylnorleucine methyl ester (DAN) or minus diazoacetyl-L-phenylalanine methyl ester (DAP) modified pepsin, respectively, demonstrated that Asp-215 is not deprotonated in pepsin. The FTIR difference spectrum of pepsin minus 1,2-epoxyparanitrophenoxypropane (EPNP) modified pepsin demonstrates that Asp-32 is present in pepsin as CO2- anion. The position of the v(C = O) vibration demonstrates that no (O...H...O)- hydrogen bond between Asp-215 and Asp-32 is formed. Furthermore, no H3O+ is present in the active center. Studies of the complex of pepsin with the inhibitor pepstatin prove that the inhibitor removes the water from the active site and Asp-32 becomes protonated.

Engineering aspartic proteases to probe structure and function relationships

Recently, protein engineering has been used to interconvert homodimeric and homologous single-chain aspartic proteases, with some success. The independent folding of the domains of these proteases has also permitted the engineering of domain-rearranged protease zymogens and the use of individual domains as probes for structural denaturation. In addition, site-directed mutagenesis has provided insights into the catalytic mechanism and specificity of this family of proteases.

Proteolytic activity and free amino acid concentrations in polymorphonuclear leucocytes

Polymorphonuclear granulocytes (PMN) are valuable tools for evaluating amino acid (AA) metabolism in nucleated cells, although variations of free amino acid concentrations due to the methods used for the separation of the cells and the procedures used for lysis have been reported. Furthermore, analytical variations in PMN AA concentration may be induced by protease activation during preparation, so that free AA detected in cells could originate from proteolysis other than from the physiological metabolic pathways and transport systems. To study this possibility we measured granulocyte protease activity and AA concentrations in cell suspensions processed with and without the addition of antiproteolytic agents. Granulocyte AA concentrations and protease activity in samples treated with antiproteolytics were 8-15 times lower than in samples processed without antiproteolytics. The use of protease inhibitors throughout the sample preparation is necessary for reliable estimation of free AA in granulocytes.

KRI-1314: an orally effective inhibitor of human renin

Biochemical and pharmacological properties of KRI-1314, a newly synthesized, low molecular weight (M.W.: 690) renin inhibitor, were investigated in vitro and in vivo. The novel amino acid norstatine, which is shorter in chain length than the well-known statine, was incorporated into KRI-1314 as a tetrahedral transition-state analogue for the Leu10-Val11 scissile peptide in the renin substrate. KRI-1314 more strongly inhibited plasma renins from primates than those from dogs, rabbits, guinea pigs and rats. KRI-1314 competitively inhibited highly-purified human renin with a Ki value of 9.9 x 10(-10) M. KRI-1314 strongly inhibited the tissue renin-like activities of various organs from Japanese monkeys, with IC50 values on the order of 10(-8) M. KRI-1314 was also very stable in various tissue homogenates from Japanese monkeys. Both intravenous (from 0.25 to 3 mg/kg) and oral (10 and 30 mg/kg) administration of KRI-1314 to anesthetized and conscious sodium-depleted Japanese monkeys, respectively, significantly lowered the blood pressure and plasma renin activity without affecting the heart rate. In Japanese monkeys, KRI-1314 was continuously detected in the plasma up to at least 7 hr after oral administration of 10 and 30 mg/kg. These results demonstrate that KRI-1314 is a highly potent, primate-selective and long-lasting oral renin inhibitor with a blood pressure lowering effect.