Antithrombotic Activity of a Novel C-Terminal Hirudin Analog in Experimental Animals

A synthetic hirudinsgs55-65 C-terminal fragment analog was evaluated for anticoagulant activity and in models of experimental thrombosis in mice and rats. Intravenous injection caused doserelated inhibition of thrombin and anticoagulation in rat blood samples, protection from thromboembolism in mice and inhibition of stasis-induced venous thrombosis in rats. Antithrombotic effectiveness corresponded with anticoagulant activity. Anephric animals exhibited longer duration of activity than normal animals suggesting the kidney as a major route of elimination.

Flavonol and imidazole derivatives block HPV16 E6 activities and reactivate apoptotic pathways in HPV⁺ cells

High-risk human papillomaviruses (HR-HPVs) cause nearly all cases of cervical cancer, as well as approximately 30% of head and neck cancers. HPV 16 E6, one of two major viral oncogenes, protects cells from apoptosis by binding to and accelerating the degradation of several proteins important in apoptotic signaling, including caspase 8 and p53. We proposed that blocking the interactions between HPV E6 and its partners using small molecules had the potential to re-sensitize HPV(+) cells to apoptosis. To test this idea, we screened libraries of small molecules for candidates that could block E6/caspase 8 binding and identified several candidates from different chemical classes. We tested hits for dose-dependency and specificity in vitro and for toxicity in a cell-based assay and then used this information to select the two best candidates for further testing: myricetin, a flavonol, and spinacine, an imidazole amino-acid derivative of histidine. Both compounds clearly inhibited the ability of E6 to bind in vitro to both caspase 8 and E6AP, the protein that mediates p53 degradation. In addition, both compounds were able to increase the level of caspase 8 and p53 in SiHa cervical cancer cells, resulting in an increase of caspase 3/7 activity. Finally, both myricetin and spinacine sensitized HPV(+) cervical and oral cancer cells, but not HPV(-) cervical and oral cancer cells, to apoptosis induced by the cancer-specific ligand TRAIL, as well as the chemotherapeutic agents doxorubicin and cisplatin. New therapies based on this work may improve treatment for HPV(+) cancer patients.

Recent advances in microwave-assisted organic syntheses

The application of microwaves to organic synthesis is opening up new opportunities for the synthetic chemist by providing new routes not practical by traditional means, such as improved reaction yields, solvent-free reaction conditions or decreasing the time needed for transformations. This is an area of synthesis that is rapidly developing. It is becoming clear that microwave approaches can be developed for most reactions requiring heating. The most interesting developments are those demonstrating the enabling of microwave reactions where traditional methods have failed or give only poor yields. This review intends to point out some of the more interesting papers in this area published over the last year or so, where the microwave method was demonstrated as clearly superior to previously available techniques or a new useful approach was presented.

Biocatalytic combinatorial synthesis

Combinatorial biocatalysis, based on a principle of the combinatorial use of biosynthetic steps rather than the combinatorial use of reagents, offers a complementary approach to combinatorial chemistry, which, used individually or in connection with synthetic organic transformations, provides access to analogues not readily accessible by chemical synthetic means alone. The issues and strategies particular to this approach are discussed. Examples are given demonstrating these principles as well as the unique advantages of achieving chemo-, regio- and stereoselectivity under mild reaction conditions that biocatalytic methods offer.

Structure-function studies on positions 17, 18, and 21 replacement analogues of glucagon: the importance of charged residues and salt bridges in glucagon biological activity

We have designed and synthesized eight compounds 2-9 which incorporate various amino acid residues in positions 17, 18, and 21 of the glucagon molecule: 2, [Lys17]glucagon amide; 3, [Lys18]glucagon amide; 4, [Nle17,Lys18,Glu21]glucagon amide; 5, [Orn17,18, Glu21]glucagon amide; 6, [d-Arg17]glucagon; 7, [d-Arg18]glucagon; 8, [d-Phe17]glucagon; and 9, [d-Phe18]glucagon. Compared to glucagon (IC50 = 1.5 nM), analogues 2-9 were found to have binding affinity IC50 values (in nM) of 0.7, 4.1, 1.0, 2.0, 5.0, 25.0, 43.0, and 32.0, respectively. When these compounds were tested for their ability to stimulate adenylate cyclase (AC) activity, they were found to be full or partial agonists having maximum stimulation values of 100, 100, 100, 100, 87, 78, 94, and 100%, respectively. On the basis of the X-ray crystal structure of [Lys17,18,Glu21]glucagon amide reported here, the ability to form a salt bridge between Lys18 and Glu21 is probably key to their increased binding and second messenger activities. Among the eight analogues synthesized here, only analogue 4 preserves the ability to form a salt bridge between Lys18 and Glu21. However, since these modifications are minor they do not seem to change the amphiphilic character of the C-terminus, allowing these analogues to reach 78-100% stimulation in the adenylate cyclase assay. Biological data from analogues 6-9 supports the idea that position 18 of glucagon may influence binding only, while position 17 may influence both receptor recognition and transduction.

RS-66271, a C-terminally substituted analog of human parathyroid hormone-related protein (1-34), increases trabecular and cortical bone in ovariectomized, osteopenic rats

It was predicted from the amino acid sequence of the bone anabolic peptides, parathyroid hormone (PTH) (1-34) and PTH related protein (PTHrP) (1-34), that the C-terminal amino acids form an amphipathic alpha-helix. Therefore, we substituted a model amphipathic alpha-helical peptide (MAP) sequence in the C-terminal region of hPTHrP(1-34), obtaining RS-66271 ([MAP1-10]22-31 hPTHrP(1-34)-NH2). The anabolic activities of RS-66271 and hPTHrP(1-34) were evaluated in 3-month-old, ovariectomized (OVX) osteopenic rats. Subcutaneous injection of hPTHrP(1-34) at 80 micrograms/kg/day partially reversed estrogen depletion trabecular bone loss but was ineffective in the cortex. In contrast, RS-66271 dose-relatedly reversed loss at both sites and, at 80 micrograms/kg/day, returned both trabecular and cortical bone calcium to the level of sham-operated controls. Histomorphometric analysis showed significantly elevated bone formation rates over vehicle-treated OVX in both trabecular and cortical tibial bone following treatment with RS-66271. Electron microscopy showed an increase in the relative surface area of vertebral trabeculae covered by osteoblasts in animals treated with RS-66271. These studies demonstrate that the C-terminal amino acids of hPTHrP(1-34) can be replaced by a model amphipathic helix and that the new chemical entity has greater anabolic activity than the parent peptide. The results suggest that RS-66271 may be a candidate molecule for the treatment of human osteoporosis.

Combinatorial synthesis of small-molecule libraries using 3-amino-5-hydroxybenzoic acid

A non-peptide library of 2001 compounds has been prepared utilizing solid-phase techniques. The split/combine method was demonstrated to work well to form mixtures of compounds based on 3-amino-5-hydroxybenzoic acid as a core structure. The benzoic acid of the core structure served as the attachment point for the resin and the amino and hydroxy positions were variably substituted.

Modulation of osteogenic cell ultrastructure by RS-23581, an analog of human parathyroid hormone (PTH)-related peptide-(1-34), and bovine PTH-(1-34)

RS-23581, a synthetic analog of human PTH-related protein-(1-34), and the amino-terminal 34 amino acids of bovine PTH [bPTH-(1-34)] increase bone mineral density. We wished to determine how quickly the ultrastructure of the osteogenic cells, i.e. osteoblasts and lining cells, of the cancellous bone of the second lumbar vertebra of ovariectomized rats was altered in response to the initiation and cessation of treatment. Ovariectomized rats were injected daily with 80 micrograms/kg RS-23581, bPTH-(1-34), or vehicle for 19 days. Animals were killed throughout the treatment period and during the ensuing 10 days. By 5 days after the initiation of treatment with either peptide, the cells on the trabecular surface were predominantly (> 90%) osteoblasts, with only a small increase in the total cell number. Throughout the dosing period, the relative area of the cytoplasm of osteogenic cells from rats treated with RS-23581 or bPTH-(1-34) was greater than that of cells from the ovariectomized control group, suggesting a relationship between bone formation and cytoplasmic mass. By 7 days after the cessation of treatment, the trabecular surface was covered predominantly by lining cells without a change in cell number. Thus, these peptides apparently promote the osteoblast phenotype; the osteoblasts revert to lining cells after the peptides are withdrawn.

Binding of fluorescent and spin-labeled C-terminal hirudin analogs to thrombin

Synthetic peptides based on the sequence of the negatively charged carboxyl tail of hirudin exhibit anticoagulant activity. Several antithrombin agents are being developed by chemical and structural optimization of these "hirupeptides". The present work demonstrates the design and use of novel spin-labeled and fluorescent-labeled C-terminal hirudin analogs to study the interactions of these antithrombin agents with thrombin in solution. Three labeled hirulabels were synthesized based upon the amino acid sequence of the antithrombin agent MDL 28050, X-NH-(CH2)7-CO-Asp-Tyr-Glu-Pro-Ile-Pro-Glu-Glu-Ala-Cha-D-Glu-OH, where X = anthraniloyl, 1,5-dansyl, or 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrrolin-1-oxyl. The modifications did not significantly alter the potency of these inhibitors which showed Ki values of 100 nM. Their interactions with human and bovine thrombin were studied by ESR and fluorescence techniques. The spin-labeled hirupeptide was able to discern subtle differences in binding to human versus bovine thrombin. The 8-aminooctanoic acid spacer arm placed the nitroxide moieties near the active site, near regions of the autolysis loops which differentiates between human alpha- and gamma-thrombin. It was also able to discern paramagnetic quenching and fluorescence energy transfer interactions, respectively, between covalently attached spin labels and fluorescent probes at the active site Ser 195 and the fluorophore on the hirupeptide.

Neuropeptide Y and truncated neuropeptide Y analogs evoke histamine release from rat peritoneal mast cells. A direct effect on G proteins?

Several regulatory peptides, including neuropeptide Y, can release histamine from mast cells. In the present study we investigated which parts of the neuropeptide Y molecule are required to evoke the release of histamine from isolated rat peritoneal mast cells. In addition, we examined whether the histamine release evoked by neuropeptide Y (and by compound 48/80) is sensitive to the G protein inhibitors pertussis toxin and benzalkonium chloride. Neuropeptide Y released histamine in a concentration-dependent manner. Also a neuropeptide Y analog with the center part substituted by 8-aminooctanoic acid, [Aoc2-27]neuropeptide Y, and the cyclic form of the C-terminal hexapeptide, cyclic neuropeptide Y-(31-36), released histamine. The three peptides were equally effective and equally potent. Neuropeptide Y-(1-24)NH2 also released histamine, but its efficacy was low. The rank order of potency of the analogs tested did not agree with that of any of the previously known or postulated neuropeptide Y receptors. Pretreatment of mast cells with pertussis toxin or benzalkonium chloride markedly inhibited the histamine release evoked by neuropeptide Y, [Aoc2-27]neuropeptide Y and compound 48/80. In conclusion, most of the histamine-releasing activity of neuropeptide Y resides in the six C-terminal amino acid residues. The release appears to be G protein-dependent and is probably not receptor mediated.

Structures of thrombin complexes with a designed and a natural exosite peptide inhibitor

The structures of two hirudin-based fibrinogen recognition exosite peptide inhibitors with significantly different sequences complexed with alpha-thrombin at a site distinct from the active site (exosite) have been determined crystallographically at 2.2 and 2.3 A resolution. One is a designed synthetic peptide with some nonconventional amino acid residues (MDL-28050), and the other is a natural COOH-terminal peptide isolated from the leech Hirudinaria manillensis (hirullin P18). The structures have been refined by restrained least squares methods to R values of 0.161 and 0.155, respectively. The first stretch of each peptide, corresponding to hirudin 55-59, associates with thrombin similar to hirudin and hirugen (hirudin 53-64). Although the remaining residues of the inhibitors interact with and bind to thrombin, the binding is accomplished. through a rigid body conformational adjustment of the peptide with respect to the conformation displayed by hirudin and hirugen (40 degrees rotation about the Ile59, CA-C bond). This causes the side groups of cyclohexylalanine 64' of MDL-28050 and Ile60, of hirullin to point in the opposite direction of the all important Tyr63, ring of hirudin and hirugen but permits the residues to penetrate and interact with the 3(10) turn hydrophobic binding pocket of thrombin. Thus, the hydrophobic interaction is accomplished in a different way by virtue of the substrate conformational readjustment. The results show that the first stretch of peptide makes concerted and efficient binding interactions with thrombin, and the peptide positions of the inhibitors are fairly specific and homologous so that the stretch appears to be related to specific recognition associated with the exosite. The relative flexibility of structure and sequence of the second stretch is a display of tolerance of imprecision by thrombin in its COOH-terminal hydrophobic association with hirudin-based inhibitors.

Activation of neuropeptide Y1 and neuropeptide Y2 receptors by substituted and truncated neuropeptide Y analogs: identification of signal epitopes

Neuropeptide Y (NPY-(1-36)) acts on Y1 and Y2 receptors at the sympathetic neuroeffector junction. Various truncated NPY analogs were tested in the isolated guinea-pig caval vein where NPY is a vasoconstrictor (Y1 receptors) and in isolated rat vas deferens, by monitoring the suppression of electrically evoked contractions (Y2 receptors). The aim of this study was to define which parts of the NPY-(1-36) molecule were required to activate these receptors. NPY-(1-36), [Pro34]NPY and [Glu16,Ser18,Ala22,Leu28,31]NPY (ESALL-NPY), the latter being an analog with increased alpha-helicity in the 14-31 region, evoked vasoconstriction with similar potency and efficacy. Cyclic as well as linear NPY analogs having the 4 to 7 N-terminal amino acid residues linked to the 9 to 19 C-terminal residues by an 8-aminooctanoic acid (Aoc) residue were 25-50 times less potent than NPY-(1-36) itself. In the cyclic analogs, a disulfide bond was introduced to bring the N- and C-termini close together. Linear Aoc-2-27-NPY was virtually inactive. The Y1 receptor needs an intact N-terminal end of NPY in order to become fully activated. The requirements for the C-terminus are less stringent, since substitutions in this part of the molecule resulted in fully active analogs. The central portion of the molecule may impose steric constraints on the N- and C-terminal ends, thereby facilitating Y1 receptor activation, but it does not seem to be essential for receptor recognition. NPY-(2-36) and NPY-(5-36) were only slightly less potent than the parent molecule in suppressing electrically evoked twitches in the vas deferens.(ABSTRACT TRUNCATED AT 250 WORDS)

An amphipathic alpha-helical decapeptide in phosphatidylcholine is an effective synthetic lung surfactant

An idealized model amphipathic alpha-helical decapeptide was synthesized and tested for efficacy as a totally synthetic lung surfactant in simple mixtures with dipalmitoylphosphatidylcholine (DPPC). Quasi-static lung compliance was restored to 92 +/- 3% of the unlavaged value at a pressure of 5 cm H2O in an in vitro lavaged rat lung model. A sustained improvement in gas exchange was also observed when guinea pigs were treated with the synthetic lung surfactant in an in vivo lavaged lung model. DPPC/peptide mixtures rapidly formed low surface tension films in the pulsating bubble surfactometer consistent with a mechanism in which the lipid and peptide mixture spreads rapidly in the lavaged lung to minimize the surface tension at the air/tissue interface. This decapeptide sequence is active in mixtures with DPPC whether the residues are in the all L or all D conformation. However, a peptide with identical sequence, but with alternating D and L amino acid residues, is relatively inactive. Positive charge interactions are not important since a peptide with formylated lysine residues is active. The activity of these decapeptides, with sequences unrelated to any of those in natural lung surfactants, shows that the classic amphipathic alpha-helical hypothesis may be useful in designing peptides that will be effective synthetic lung surfactants in binary mixtures with DPPC. The data demonstrate that a small water-soluble synthetic peptide containing an amphipathic alpha-helical structure combined solely with the major lipid of natural lung surfactant is effective in restoring lung compliance and gas exchange in surfactant-deficient lungs and may be useful in treatment of the respiratory distress syndromes.

The fibrinogen anion-binding exosite of thrombin is necessary for induction of rises in intracellular calcium and prostacyclin production in endothelial cells

Thrombin stimulation of prostacyclin (PGI2) synthesis by cultured human umbilical vein endothelial cells (HUVEC) requires the active site of thrombin and involves rapid and transient rises in cytoplasmic free calcium [Ca2+]i. In this study, we investigated whether or not the anion-binding exosite for fibrinogen recognition of thrombin (which confers certain substrate specificities) is also necessary for the induction of rises in [Ca2+]i and PGI2 production. Thrombin variants which lack either the catalytic site (DIP-alpha-thrombin) or anion-binding exosite (gamma-thrombin) either alone or in combination failed to induce rises in [Ca2+]i or PGI2 production in HUVEC. To further study the role of the anion-binding exosite of thrombin in the activation of HUVEC, COOH-terminal fragments of hirudin were used. This portion of hirudin interacts with the anion-binding exosite of thrombin and inhibits thrombin-induced fibrinogen coagulation while leaving the catalytic activity of thrombin intact. A 21-amino acid COOH-terminal peptide of hirudin (N alpha-acetyldesulfato-hirudin45-65 or Hir45-65) inhibited thrombin-induced (0.5 U/ml) rises in [Ca2+]i and PGI2 production with IC50 of 0.13 and 0.71 microM, respectively. Similar results were obtained using shorter hirudin-derived peptides. Thus, the fibrinogen anion-binding exosite of thrombin is required for alpha-thrombin-induced rises in [Ca2+]i and PGI2 production in HUVEC.

Mixtures of synthetic peptides and dipalmitoylphosphatidylcholine as lung surfactants

Synthetic peptides that differ in their lipid-peptide interactions were combined with dipalmitoylphosphatidylcholine (DPPC) and tested in an adult rat lavaged lung model in vitro for efficacy as totally synthetic lung surfactants. The putative amphipathic alpha-helical region of the major lung surfactant apoprotein (SP-A81-102), an analogue with increased amphipathic alpha-helical potential ([Lys88,97,Glu99,Trp102]-SP-A81-102]), and the hydrophobic peptide gramicidin D were all ineffective. Three water-soluble lipid-binding peptides that contain amphipathic alpha-helical regions were also tested. Of these, only a 24-residue amphipathic alpha-helical peptide (18As) based on the lipid-binding sequences of the plasma apolipoproteins was effective. Melittin and glucagon were ineffective. Mixtures of 18As and DPPC also restored gas exchange in an in vivo lavaged guinea pig lung model to 90-95% of its prelavage value and maintained it for at least 3 h. Mixtures of DPPC and 18As are also surface active (gamma min less than 4 mN/m in the pulsating bubble). These data demonstrate the efficacy of a combination of a single lipid and a small, water-soluble, nonhemolytic, synthetic peptide containing an amphipathic alpha-helical structure and a sequence unrelated to any of the reported lung surfactant apoprotein sequences.

Specific inhibition of binding of antistasin and [A103,106,108] antistasin 93-119 to sulfatide (Gal(3-SO4)beta 1-1Cer) by glycosaminoglycans

Leech-derived antistasin is a potent anticoagulant and antimetastatic protein that binds sulfatide (Gal(3-SO4)beta 1-1Cer) and sulfated polysaccharides. In this study, the synthetic fragment [A103,106,108] antistasin 93-119, which corresponds to the carboxyl terminus, showed specific and saturable binding to sulfatide. Binding was competitively blocked by glycosaminoglycans (GAGs) in the order: dextran sulfate 5000 congruent to dextran sulfate 500,000 greater than heparin greater than dermatan sulfate much greater than chondroitin sulfates A and C. This rank order of inhibitory potency was identical to that observed with whole antistasin. We suggest that residues 93-119 of antistasin represent a critical domain for binding GAGs and sulfated glycolipids.

Heparin Binding Properties of the Carboxyl Terminal Domain of [A103,106,108] Antistasin 93–119

Antistasin is a 119 amino acid protein with anticoagulant, antimetastatic and heparin-binding properties derived from the salivary glands of the leech Haementaria officinalis (1). This protein contains a specific consensus sequence for heparin binding at its carboxyl terminal end and a region between residues 32 and 48 putatively involved in glycosaminoglycan interactions. The cyclic peptide antistasin 37-48 (C-P-H-G-F-Q-R-S-R-Y-G-C) and the carboxyl terminal fragment [A103,106,108] antistasin 93-119 (P-N-G-L-K-R-D-K-L-G-A-E-Y-A-E-A-R-P-K-R-K-L-I-P-R-L-S) were synthesized by solid-phase peptide chemistry and their interactions with 125I-labeled heparin were investigated. Heparin binding to [A103,106,108] antistasin 93-119 was specific and saturable as binding was blocked by addition of the unlabeled glycosaminoglycan. The rank order of potency of various glycosaminoglycans in blocking 125I-labeled heparin binding to [A103,106,108] antistasin 93-119 was dextran sulfate greater than heparin much greater than dermatan sulfate greater than or equal to chondroitin sulfate A and C indicating a specificity of the peptide for the glycosaminoglycan structure. Moreover, heparin binding increased linearly with increasing salt and was optimal at 0.15 M NaCl and physiological pH. In contrast, binding of heparin to the basic peptide antistasin 37-48 decreased linearly as the ionic strength of the medium was increased to physiological concentration (0.15 M) thus showing a greater specificity of heparin for [A103,106,108] antistasin 93-119. These studies indicate that residues 93-119 of antistasin mediate this inhibitor's interaction with heparin.

Demonstration that [A103,106,108] antistasin 93-119 inhibits the specific binding of antistasin to sulfatide [Gal(3-SO4)beta 1-1Cer]

Antistasin is a 119 amino acid heparin-binding protein from the leech Haementaria officinalis which has anticoagulant and antimetastatic properties. A series of peptides representing the basic amino acid-rich domains of the amino- and carboxyl-terminal regions of the inhibitor were synthesized by solid-phase peptide chemistry and their ability to bind sulfated glycolipids was investigated. The findings show that [A103,106,108] antistasin 93-119 has high affinity for sulfatide and inhibits the specific interaction of whole antistasin with [Gal(3-SO4)beta 1-1Cer]. We conclude that the 93-119 region is a critical domain that mediates the interaction of antistasin with sulfated glycolipids.

Examination of the peptide sequence requirements for lipid-binding. Alternative pathways for promoting the interaction of amphipathic alpha-helical peptides with phosphatidylcholine

To examine the relationship between peptide sequence and the interaction of amphipathic alpha-helical peptides with phosphatidylcholines, various methods of mixing the peptide and lipid were explored. A series of amphipathic alpha-helical peptides containing from 10 to 18 residues were synthesized by solid-phase techniques. An 18-residue peptide and two relatively hydrophobic 10-residue peptides did not disrupt dimyristoylphosphatidylcholine liposomes when added to the lipid in buffer. However, when the peptides were premixed with lipid in a suitable organic solvent and then reconstituted with aqueous buffer, clear micelles were formed, indicating association of the amphipathic alpha-helical peptide with lipid. In general, the best solvent for this purpose was trifluoroethanol. The circular dichroic and fluorescence spectra of peptides which readily formed clear mixtures when mixed in buffer with dimyristoylphosphatidylcholine liposomes were similar when prepared either by the alternative pathway technique using trifluoroethanol or by a cholate removal technique. For the peptides which did not clear liposomes in buffer, first mixing with dimyristoylphosphatidylcholine in trifluoroethanol resulted in an increase in the alpha-helicity of the peptides as judged by circular dichroic spectra and a blue-shift in the fluorescence emission maxima of the single tryptophan residue in each peptide. These data are consistent with formation of an amphipathic alpha-helix in lipid by peptides which based on mixing experiments with dimyristoylphosphatidylcholine liposomes in buffer at the phase transition temperature of the lipid would be considered ineffective in lipid binding. Thus, simple mixing of peptides with liposomes may give misleading results concerning the intrinsic affinity of a particular peptide sequence for lipid. In addition, the data demonstrate that relatively hydrophobic amphipathic alpha-helical peptides which do not form small micelles with dimyristoylphosphatidylcholine spontaneously in aqueous solution may interact with lipid as typical amphipathic alpha-helices when mixed by an alternative pathway.

Effect of the hirudin carboxy-terminal peptide 54-65 on the interaction of thrombin with platelets

The carboxy-terminal region of hirudin (residues 54-65) has previously been shown to inhibit thrombin clotting activity without binding to the catalytic site of the enzyme. In the present study, the effect of hirudin 54-65 on thrombin interaction with specified platelet proteins has been investigated. Hirudin 54-65 was found to inhibit thrombin-induced platelet aggregation and secretion in a dose-dependent manner. Substitution of either Phe56, Glu57, Ile59, Pro60 or Leu64 showed that these residues were critical for inhibition of thrombin-induced platelet activation whereas sulfation of Tyr63 increased the inhibitory potency of the peptide. Hydrolysis of glycoprotein V, a platelet membrane substrate for thrombin, was only partially inhibited by hirudin 54-65. Although hirudin 54-65 did not decrease the amount of thrombin bound to platelets during cross-linking experiments, it was found to inhibit the specific binding of thrombin to platelet glycoprotein Ib. Since the carboxy-terminal region of hirudin has previously been reported to bind near the trypsin-catalyzed beta cleavage site, we have analyzed the consequences of alpha to beta-thrombin conversion on both thrombin-hirudin 54-65 interaction and thrombin activity toward platelets. The beta cleavage induced a decrease in the affinity of thrombin for both glycoprotein Ib and hirudin 54-65. Altogether, our results indicate that thrombin recognition sites for hirudin 54-65 and platelet membrane glycoprotein Ib share common structures located near the beta cleavage site at Arg 73 on the thrombin B chain.

Antithrombotic activity of a novel C-terminal hirudin analog in experimental animals

A synthetic hirudin55-65 C-terminal fragment analog was evaluated for anticoagulant activity and in models of experimental thrombosis in mice and rats. Intravenous injection caused dose-related inhibition of thrombin and anticoagulation in rat blood samples, protection from thromboembolism in mice and inhibition of stasis-induced venous thrombosis in rats. Antithrombotic effectiveness corresponded with anticoagulant activity. Anephric animals exhibited longer duration of activity than normal animals suggesting the kidney as a major route of elimination.

Positional effects of sulfation in hirudin and hirudin PA related anticoagulant peptides

C-Terminal fragment analogues of the leech protein hirudin or the related protein hirudin PA block thrombin's cleavage of fibrinogen. Three series of synthetic peptides were synthesized to study the effects of sulfation in hirudin-derived peptides. Potency of hirudin analogues increased with p-(amino)Phe63, p-(aminosulfonate)Phe63, and p-(sulfate)Tyr63 substitution in place of Tyr63. Sulfation of Tyr56, which in hirudin is normally Phe, resulted in a loss of 1 order of magnitude in potency. The sulfation of Tyr64 of the hirudin PA related analogue resulted in increased potency as for the hirudin analogue. However, in this series the p-(amino)Phe64 and p-(amino-sulfonate)Phe64 did not have increased potency. In addition to these positional effects, replacing all the Glu residues with (O-sulfato)Ser yielded an analogue with full antithrombin potency.

The effects of selective amino acid substitution upon neuropeptide Y antisecretory potency in rat jejunum mucosa

The antisecretory potency of NPY and a series of truncated and structural analogues of NPY have been tested upon mucosal preparations of rat small intestine. Single amino acid substitutions, i.e., [Ile34]NPY, [Pro34]NPY, resulted in severe attenuation and loss of biological activity, respectively, and neither peptide affected NPY responses. An agonist order of potency: NPY greater than or equal to [Glu16,Ser18,Ala22,Leu28,31]NPY (ESALL-NPY) greater than [Cys2,Aoc5-24,DCys27]NPY (C2-NPY) greater than [Aoc5-24]NPY greater than [Des-Ser3,Des- Lys4]C2-NPY much greater than [Cys5,Aoc7-20,DCys24]NPY (C5-NPY) greater than equal to [DCys7,Aoc8-17, Cys20]NPY (C7-NPY) greater than [Aoc8-17]NPY greater than or equal to [Ile34]C7-NPY much greater than [Aoc2-27]NPY much greater than [Pro34]C2-NPY was obtained. The use of analogues based upon the tertiary structural model of NPY with varying amounts of N- and C-terminal helical regions removed and replaced with a single 8-aminooctanoic acid residue (Aoc) has allowed us to assess the structural requirements for activation of the regions in close apposition to each other. The polyproline helix, beta-turn and majority of the amphipathic alpha-helix serve a structural role bringing N- and C-terminal residues together for optimal receptor recognition and activation.

Structure-function relationships of the C-terminal functional domain of hirudin and its variants

The C-terminal functional domain of hirudin, hirudin variant 1 (residues 55-65), binds to a non-catalytic site on thrombin. In doing so, it is capable of inhibiting the procoagulant actions of thrombin. In terms of free energy of binding, this domain, which comprises 17% of the total sequence of the protein, contributes approximately half of the binding energy of the whole protein to thrombin. This situation also appears to hold true for the known variants of hirudin, some of which differ in the functional nature of their C-terminal regions. Extensive structure-function studies on this domain yield insights into the differences and similarities in the modes of thrombin interaction of hirudin and its variants. In particular, hirudin and hirudin PA have a similar and somewhat interchangeable structure-activity relationships (SAR) profile that indicates that they interact with thrombin in a similar manner. Hirullin P18, a 62 amino acid member of the hirudin family and isolated from Hirudinaria manillensis, is substantially different in sequence and its SAR, which shows that, although it seems to utilize the same non-catalytic binding domain as hirudin, it must utilize a different mode of interaction with thrombin.

Minimal peptide length for interaction of amphipathic alpha-helical peptides with phosphatidylcholine liposomes

The interactions of a series of amphipathic alpha-helical peptides containing from 6 to 18 amino acid residues with dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) were studied by optical and calorimetric methods. Several peptides rapidly decreased the turbidity of DMPC and DPPC liposomes when mixed at the phase transition temperatures of the lipids. The extent of the clearing depended upon the chain length of the peptides, with the most effective clearing attained with peptides 10-12 residues in length. An eight-residue peptide was somewhat less effective and a six-residue peptide had no effect on liposome structure. The peptides formed small micellar structures, as judged by gel filtration chromatography. The effects of the peptides on the phase transitions of the lipids were examined by differential scanning calorimetry. The peptides that were most effective in disrupting the liposomes and forming clear micelles were also most effective in reducing the enthalpy of the gel to liquid-crystalline phase transition of the lipid. The addition of DMPC or DPPC liposomes to the peptides increased the magnitude of the negative bonds at 208 and 222 nm in circular dichroism measurements, consistent with the expected formation of alpha-helical structure on binding to lipid. The extent of burial of the single tryptophan residue in the peptides was determined by fluorescence spectroscopy. In peptides that bound to lipid, the tryptophan was in a less solvent-exposed environment in the presence of lipid, as evidenced by a blue shift in the fluorescence emission maximum of the peptide.(ABSTRACT TRUNCATED AT 250 WORDS)

Centrally truncated neuropeptide Y analog acts as an agonist for Y1 receptors on SK-N-MC cells

The similarity of neuropeptide Y (NPY) to pancreatic polypeptide (PP), whose X-ray crystallographic structure is known, has allowed computer-assisted molecular modelling of NPY and predictions of its three-dimensional structure. Utilizing these techniques, Krstenansky et al. (Proc. Natl. Acad. Sci. U.S.A., 86 (1989) 4377-4381) reported that a centrally truncated analog of porcine NPY, [D-Cys7-Aoc8-17-Cys20]pNPY, which was designed to maintain the tertiary structure of the native molecule, bound to sites on membranes from mouse brain with even higher affinity than native NPY. As brain membranes may represent a heterogeneous mixture of receptor subtypes, we decided to characterize the activity of this analog on a defined cell line. SK-N-MC cells are a human epithelioma cell line with high-affinity receptors of the Y1 subtype which are coupled to inhibition of adenylate cyclase. (D-Cys7-Aoc8-17-Cys20]pNPY bound to receptors on SK-N-MC cells, but in contrast to membranes from mouse brain, with a lower affinity than pNPY. Furthermore, [D-Cys7-Aoc8-17-Cys20]pNPY was able to inhibit isoproterenol-stimulated cAMP production in these cells. Therefore, it appears that the central amino acids deleted from this analog are not involved in NPY binding, and biological activity can be maintained by conservation of the tertiary structure of NPY around the binding surface.

C-terminal modifications of neuropeptide Y and its analogs leading to selectivity for the mouse brain receptor over the porcine spleen receptor

Neuropeptide Y (NPY) is known to bind to at least two types of receptors (Y1 & Y2). One type (Y2) is able to bind and undergo activation by both NPY and its C-terminal fragments with good potency while the other (Y1) requires the full length of NPY for good potency. For most NPY analogs that have been examined, potency for the Y2 system (porcine spleen) is greater than or equal to that for the Y1 system (mouse brain), since the Y2 system is generally less selective. However, modifications of NPY and its analogs at position 34 can lead to materials with some Y1 selectivity. For example, [Pro34]-pNPY binds to mouse brain with an affinity of 0.14 nM. Its affinity for porcine spleen is 140 nM. [His34]-pNPY was also found to be Y1 selective (19-fold), but not to the degree of the [Pro34] analog (1000-fold). The Pro34 modification in the Y2 selective C-terminal fragment NPY (20-36) converted it into an essentially non-selective analog. The selectivity from the Pro34 substitution results from a loss of Y2 binding potency along with little effect on the Y1-receptor binding. Therefore, Y1 and Y2 receptors have differing requirements for the C-terminal region of NPY in addition to their different requirements for NPY's N-terminus.

Characterization of a monoclonal antibody specific to the amino terminus of the alpha-chain of human fibrin

A peptide, Gly-Pro-Arg-Val-Val-Glu, corresponding to the first six residues of the amino terminus of the alpha-chain of human fibrin (desAA-fibrin) was prepared by solid-phase peptide synthesis. The peptide was covalently linked to keyhole-limpet hemocyanin (KLH) and used as an immunogen for preparing monoclonal antibodies. A monoclonal antibody specific to the hexapeptide, but not to KLH or fibrinogen, was produced. The antibody did not bind to thrombin-mediated clots prepared from either plasma or purified fibrinogen. However, immunoreactivity was detected when fibrin (prepared from fibrinogen) was solubilized with 8 M urea. In contrast, a monoclonal antibody specific to the amino terminus (Gly-His-Arg-Pro-Leu-Asp-Lys) of the beta-chain of fibrin recognized the epitope in clots. These results indicate that thrombin cleavage of fibrinogen produces a structural change in the amino terminal domain of the alpha-chain that makes it inaccessible to antibody interaction. In addition, our study suggests that the potential clinical application of monoclonal antibodies to localize fibrin-rich thrombi must take into account the final structure of clots.

Lipid and membrane interactions of neuropeptide Y

The interactions of neuropeptide Y with dimyristoylphosphatidylcholine and cell membranes were examined by several physical techniques to probe the potential role of its putative C-terminal amphipathic alpha-helix. Neuropeptide Y binding was demonstrated by a rapid release of entrapped 6-carboxyfluorescein and a rapid decrease in the turbidity of dimyristoylphosphatidylcholine liposomes. In addition, an increase in tyrosine fluorescence intensity and an increase in the anisotropy of diphenylhexatriene in dimyristoylphosphatidylcholine liposomes was observed. In isolated, aortic smooth muscle cell membranes, the anisotropy of diphenylhexatriene increased as a function of added neuropeptide Y. The concentration range (low microM) over which neuropeptide Y increases the polarization of diphenylhexatriene in cell membranes is similar to the range in which it inhibits isoproterenol-stimulated cAMP accumulation. This inhibition is not affected by pertussis toxin, nor does neuropeptide Y cause the release of preloaded [3H]adenine from cells into the medium. These data suggest that neuropeptide Y contains an amphipathic alpha-helical region which interacts with lipids in much the same way as the amphipathic alpha-helical regions of the plasma apolipoproteins and that the inhibition of isoproterenol-stimulated cAMP accumulation at low microM concentrations of peptide may be the result of an alteration in the cell membrane bilayer structure.

Development of MDL 28,050, a small stable antithrombin agent based on a functional domain of the leech protein, hirudin

MDL 28,050 is a decapeptide antithrombin agent that inhibits alpha-thrombin-induced fibrin clot formation by binding to a non-catalytic site on alpha-thrombin. It is the result of chemical and structural optimization of a functional domain of the leech anticoagulant, hirudin. In contrast to the contention that the polyanionic nature of this C-terminal functional domain governs its interaction with alpha-thrombin, systematic study of this region has shown the importance of the lipophilic residues for providing the functionality necessary for potent binding to alpha-thrombin. The development of MDL 28,050 and other effective antithrombin agents are outlined through the description of the structure-activity relationships (SAR) for these peptides. These peptides are effective in a variety of in vitro and in vivo models of thrombosis.

Examination of the role of the amphipathic alpha-helix in the interaction of neuropeptide Y and active cyclic analogues with cell membrane receptors and dimyristoylphosphatidylcholine

To test the potential importance of the putative C-terminal amphipathic alpha-helical region of neuropeptide Y (NPY) in receptor binding, the interactions of porcine NPY and several peptide analogues with lipid and cell membrane receptors were compared. Cyclic analogues were designed to constrain the N- and C-terminal regions of the peptide and to retain the folded conformation of NPY predicted from its sequence analogy with pancreatic polypeptide and its similar spectral behavior. The three cyclic peptides were [Cys2, 8-aminooctanoic acid5-24, D-Cys27]-NPY (C2-NPY), [Cys5, 8-aminooctanoic acid7-20, D-Cys24]-NPY (C5-NPY), and [D-Cys7, 8-aminooctanoic acid8-17, Cys20]-NPY (C7-NPY). All of the peptides bind with high affinity to pig spleen membranes, but only NPY and [Glu16, Ser18, Ala22, Leu28,31]-NPY (ESALL-NPY) bind quantitatively to dimyristoylphosphatidylcholine (DMPC) liposomes. C7-NPY and NPY20-36 bind with moderate affinity to liposomes, but only NPY and C7-NPY bind with high affinity to mouse brain receptors. Thus, lipid binding and receptor binding are not correlated in this series of peptides, and binding to the pig spleen receptor appears to require only the C-terminal region of the peptide. Simple lipid binding, as in NPY20-36, is insufficient for binding to the mouse brain receptor, suggesting that the N-terminal region of the peptide is required for high-affinity binding to this receptor. Data from fluorescence, differential scanning calorimetry, and liposome clearing experiments suggest that, although the interaction of NPY with lipid is consistent with formation of an amphipathic alpha-helix, a simple amphipathic alpha-helical model for the interaction with the high-affinity NPY receptor is insufficient to explain the data.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of micelle diameter on tryptophan dynamics in an amphipathic helical peptide in phosphatidylcholine

The effect of dimyristoylphosphatidylcholine (DMPC) on the conformation and environment of the single tryptophan residue of a model amphipathic helical polypeptide has been investigated by fluorescence quenching with a water-soluble, neutral quencher (acrylamide) and multiple-frequency phase fluorometry. The peptide H-Ser-Ser-Ala-Asp-Trp-Leu-Lys-Ala-Phe-Tyr-Asp-Lys-Val-Ala-Glu-Lys-Leu-Ly s-Glu- Ala-Phe-Ser-Ser-Ser-OH [18As; Kanellis, P., Romans, A.Y., Johnson, B.J., Kercret, H., Chiovetti, R., Jr., Allen, T.M., & Segrest, S.P. (1980) J. Biol. Chem. 255, 11464] was synthesized by solid-phase techniques. Peptide was incubated at 26 degrees C with DMPC at various peptide:lipid weight ratios. The diameter of the resulting disk-shaped micelles increases with increasing lipid concentration from 12.0 +/- 0.4 nm at a 1:1 weight ratio of peptide to lipid to a maximum of 48.7 +/- 1.0 nm at a 1:13 ratio. At a weight ratio of 1:5, the average diameter is 22.7 +/- 0.6 nm. Decreasing the peptide:lipid ratio of the micelle resulted in a blue-shift in the fluorescence emission maximum (from 337 nm at 1:1 to 334 nm at 1:5), an increase in the fluorescence lifetime of the tryptophan measured by the phase shift method at 18 MHz (from 3.12 ns at 1:1 to 3.61 ns at 1:5), a decrease in the rate of fluorescence quenching by acrylamide (from 0.87 x 10(9) M-1 s-1 at 1:1 to 0.42 x 10(9) M-1 s-1 at 1:5), and an increase in the activation energy for quenching (from 6.7 kcal/mol at 1:1 to 12.7 kcal/mol at 1:5).(ABSTRACT TRUNCATED AT 250 WORDS)

Preparation of antibodies to a synthetic C terminus of hirudin and identification of an antigenic site

Hirudin is a 65 amino acid anticoagulant peptide produced in the leech. The single polypeptide is cross-linked by three disulfide linkages in the NH2 terminal half of the molecule. A peptide corresponding to the COOH terminus (residues 45-65) was synthesized utilizing lysine 47 as a specific residue to conjugate to thyroglobulin as a carrier for raising antibodies in mice. Using an enzyme-linked immunosorbent assay (ELISA) technique, it was found that the major antigenic domain(s) was located between residues 52-65. The COOH terminal residues Ile-59, Tyr-63, and Leu-64 are crucial for maintaining the antigenic structure. The NH2 terminal region (residues 45-52) that is proximal to the carrier protein, however, was not immunoreactive. A possible mechanism by which antibodies recognize the COOH terminal region of the synthetic peptide and the strategy for raising such antibodies are discussed.

Centrally truncated and stabilized porcine neuropeptide Y analogs: design, synthesis, and mouse brain receptor binding

Porcine neuropeptide Y (pNPY) has been proposed to form an intramolecularly stabilized structure characterized by N- and C-terminal helical regions arranged antiparallel due to a central turn region. Analogs based on this structural model that have the central turn region and various amounts of the helical regions removed, yet retain the N and C termini in a similar spatial orientation were designed. The gap formed by removal of the central residues (residues 8-17 or 7-20) was spanned with a single 8-aminooctanoic acid residue (Aoc) and the structure was further stabilized by the introduction of a disulfide bridge. [D-Cys7,Aoc8-17,Cys20]pNPY and [Cys5,Aoc7-20,D-Cys24]pNPY were synthesized and found to have receptor binding affinities of 2.3 nM and 150 nM, respectively, in mouse brain membranes (pNPY affinity is 3.6 nM in this assay). It is proposed that the central region (residues 7-17) of pNPY serves a structural role in the peptide and is not involved in direct receptor interaction.

C-terminal peptide alcohol, acid and amide analogs of desulfato hirudin54-65 as antithrombin agents

Analogs of the antithrombin peptide hirudin54-65 with C-terminal modifications have been synthesized in order to examine the requirements for alpha-thrombin inhibition. The C-terminal residue, Gln65, could be replaced with L-amino acids or amino alcohols with neutral or charged hydrophilic side chains without greatly affecting the peptide's antithrombin potency as determined by inhibition of thrombin-induced clot formation in human plasma in vitro. Derivatives with D- or L-amino carboxamides at position 65 had significantly reduced potency, but still retained activity. Deletion of residue 65 with conversion of residue 64 to the amide or alcohol derivative resulted in a three-fold loss of potency. In addition to these results the solid-phase synthesis of peptide alcohols via direct displacement of p-nitrobenzhydrylideneisonitroso resin attached peptides with the desired C-terminal amino alcohol is reported.

Short model peptides having a high alpha-helical tendency: design and solution properties

Secondary structure is not typically observed for small peptides in solution. Several of the properties of alpha-helical peptides are known which lead to the stabilization of the structure. The utilization of all the known factors important for alpha-helical stabilization in the design of model alpha-helical peptides (MAP) is reported. The peptides are based on the repeating eleven amino acid sequence, Glu-Leu-Leu-Glu-Lys-Leu-Leu-Glu-Lys-Leu-Lys (MAP1-11). The CD spectra of these peptides give evidence for more alpha-helical content than has been reported for any short peptide (less than 18 amino acids) to date. This alpha-helical tendency does not require the presence of lipid or reduced temperature. For instance, Suc-[Trp9]MAP9-3'' amide (5), a seventeen amino acid peptide has 100% and 80% alpha-helical contents at 1.7 x 10(-4) M and 1.7 x 10(-5) M, respectively. Suc-[Trp9]MAP2-11 amide (3), merely ten amino acids in length, is 51% alpha-helical at 1.7 x 10(-4) M in 0.1 M phosphate buffer at room temperature. In the presence of lipid or trifluoroethanol, the alpha-helical content of these peptides is increased. This series of peptides demonstrates the complimentarity of various secondary structure design principles and the extent to which structure can be induced in small linear peptides.

Human hepatoma (HepG2) cells secrete a single 65 K dalton triglyceride lipase immunologically identical to postheparin plasma hepatic lipase

A triacylglycerol lipase was isolated from the culture medium of HepG2 human hepatoma cells and its properties were compared to hepatic triglyceride lipase (H-TGL) from human postheparin plasma. The HepG2 cell enzyme bound to heparin-Sepharose, was eluted with 1 M NaCl and was not inhibited by 1 M salt. Western-blotting of the fractions from the heparin-Sepharose column with a monoclonal antibody prepared against postheparin plasma H-TGL and which binds to an epitope in the carboxyl-terminus of H-TGL gave a single immunoreactive protein band of 65 kDa. This finding of immunochemical identity was confirmed with polyclonal antibodies prepared against synthetic peptides of H-TGL corresponding to amino acid residues 82-94 near the amino-terminus and residues 468-477, the carboxyl-terminus of the enzyme. We conclude that HepG2 cells secrete a single triacylglycerol lipase with molecular weight properties and immunological characteristics identical to post-heparin plasma H-TGL.

Importance of the C-terminal alpha-helical structure for glucagon's biological activity

The synthetic glucagon analogues [Glu21]glucagon, 2, and [Lys17,18,Glu21]glucagon, 3, were designed using Chou-Fasman calculations for the purpose of enhancing the probability for the formation of a C-terminal amphipathic alpha-helical conformation. Circular dichroism indicates increased alpha-helical content for these analogues in solution relative to glucagon. Analogues 2 and 3 also exhibit a 3-fold and 5-fold increase in receptor binding potency, respectively. The adenylate cyclase stimulating potencies of 2 and 3 relative to glucagon are 2.1 and 7 times greater, respectively. Attempts were made at further alpha-helical enhancement by further substitutions in the 10-13 region of glucagon, as represented by the glucagon analogues [Phe13,Lys17,18 Glu21]glucagon, 4, and [Phe10,13,Lys17,18,Glu21]glucagon, 5. These latter substitutions resulted in lowered receptor binding and adenylate cyclase potencies for 4 and 5 relative to 3 despite increased alpha-helical content in solution as observed by circular dichroism spectroscopy.

Design, synthesis and antithrombin activity for conformationally restricted analogs of peptide anticoagulants based on the C-terminal region of the leech peptide, hirudin

Synthetic peptides cyclized via disulfide linkages have been synthesized as conformationally restricted analogs of a novel class of antithrombotic peptides that inhibit fibrinogen cleavage by binding to a non-enzymatic site on thrombin. Several conformational models for these inhibitors have been considered and cyclic analogs were synthesized to test their validity. Compounds designed on an alpha-helical model yielded several cyclic analogs that retained antithrombin activity. [D-Cys58, Cys61]-hirudin54-65, 5, and [D-Cys60, Cys63]-hirudin54-65, 6, had IC50 values of 26 and 30 microM, respectively, in an in vitro clot assay compared with a value of 3.7 microM for the linear hirudin54-65.

Interaction of hirudin with thrombin: identification of a minimal binding domain of hirudin that inhibits clotting activity

Hirudin, isolated from the European leech Hirudo medicinalis, is a potent inhibitor of thrombin, forming an almost irreversible thrombin-hirudin complex. Previously, we have shown that the carboxyl terminus of hirudin (residues 45-65) inhibits clotting activity and without binding to the catalytic site of thrombin. In the present study, a series of peptides corresponding to this carboxyl-terminal region of hirudin have been synthesized, and their anticoagulant activity and binding properties to thrombin were examined. Binding was assessed by their ability to displace 125I-hirudin 45-65 from Sepharose-immobilized thrombin and by isolation of peptide-thrombin complexes. We show that the carboxyl-terminal 10 amino acid residues 56-65 (Phe-Glu-Glu-Ile-Pro-Glu-Glu-Tyr-Leu-Gln) are minimally required for binding to thrombin and inhibition of clotting. Phe-56 was critical for maintaining anticoagulant activity as demonstrated by the loss of activity when Phe-56 was substituted with D-Phe, Glu, or Leu. In addition, we found that the binding of the carboxyl-terminal peptide of hirudin with thrombin was associated with a significant conformational change of thrombin as judged by circular dichroism. This conformational change might be responsible for the loss of clotting activity of thrombin.

Comparison of hirudin and hirudin PA C-terminal fragments and related analogs as antithrombin agents

Hirudin PA54-66 and related hirudin fragment analogs were synthesized and assessed for their inhibition of thrombin-induced fibrin-clot formation in plasma. Pro58 and Ala63-Tyr64 modifications in the hirudin sequence resulted in increased antithrombin potency, whereas Asp62, Ala63 and Tyr64 individual substitutions each resulted in a loss of potency.

N-terminal requirements of small peptide anticoagulants based on hirudin54-65

C-terminal fragment analogues of the leech anticoagulant peptide hirudin represent a unique class of thrombin inhibitors that blocks thrombin's cleavage of fibrinogen but does not block the catalytic site of thrombin. In this paper, a series of synthetic peptides were prepared by solid-phase methodology to determine the optimal N-terminal and position 56 functionalities for these C-terminal fragment analogues of hirudin. Inhibition of fibrin clot formation by thrombin in vitro was used as a measure of anticoagulant activity. In the minimal C-terminal sequence necessary for anticoagulant activity, hirudin56-64, an L aromatic amino acid is required at position 56. Phe56----Tyr substitution retained potency, whereas p-Cl-Phe56 and phenylglycine56 substitutions resulted in decreased potencies. Removal of the cationic amino functionality from the vicinity of Asp55 results in increased potency (e.g., hirudin54-65, Ac-hirudin55-65) and [desNH2-Asp55]hirudin55-65 has a marked increase in potency over hirudin55-65. [DesNH2-Phe56]hirudin56-65 and related analogues show no detectable anticoagulant activity. The sensitivity of position 56 to modification demonstrates the significance of this residue in the interaction between the C-terminal region of hirudin and thrombin.

The dogfish peptides scyliorhinin I and scyliorhinin II bind with differential selectivity to mammalian tachykinin receptors

The dogfish intestinal, linear tachykinin scyliorhinin I (SCYI) and cyclic tachykinin scyliorhinin II (SCYII) bound with differential selectivity to mammalian tachykinin, membrane receptor sites. SCYI bound with highest affinity to NK-1 sites in rat submandibular gland (KI = 0.9 nM) and to NK-2 sites in hamster urinary bladder (KI = 2 nM) whereas SCYII bound with highest affinity to NK-3 sites in rat cerebral cortex (KI = 2.5 nM). These results suggest that SCYI is a dual NK-1/NK-2 tachykinin receptor agonist while SCYII is an NK-3 selective tachykinin receptor agonist.

Anticoagulant peptides: nature of the interaction of the C-terminal region of hirudin with a noncatalytic binding site on thrombin

A series of 20 C-terminal fragment analogues of the anticoagulant peptide hirudin were synthesized by solid-phase techniques in order to investigate the nature of the thrombin-hirudin interaction. Inhibition of plasma fibrin clot formation by thrombin in vitro was used as a measure of anticoagulant activity. In the minimum region necessary for detectable anticoagulant activity, hirudin56-64, positions Phe56, Glu57, Ile59, Pro60, and Leu64 are sensitive to modification. These residues are apparently important for direct interaction with thrombin or for maintaining a favorable conformation for the interaction. On the basis of conformational analysis of this region by computational methods, a "kinked" amphipathic alpha-helical structure, which orients all of the residues most critical for activity on one face of the helix, is proposed.

The synthesis, physical characterization and receptor binding affinity of neuropeptide Y (NPY)

Porcine neuropeptide Y (pNPY) was synthesized by solid-phase techniques and purified by gel filtration and reverse-phase high performance liquid chromatography. It was found to be equipotent to commercial pNPY (Peninsula) in a receptor binding assay (IC50 = 5 nM). Circular dichroic (CD) spectra of the peptide indicates a concentration-independent alpha-helical conformation in aqueous solution ([theta]222 = -13,998, 2.9 X 10(-5) M in 0.1 M sodium phosphate, pH = 8.0). Lowering the pH of the solution to 6.0 produced little change in the CD spectrum, but CD spectra at pH = 4.2 and 1.8 indicated a loss of alpha-helical content of the peptide with decreasing pH. Sedimentation equilibria of synthetic pNPY showed that it is neither wholly monomeric nor dimeric at pH = 4.2 and 8.0. These data suggest an intramolecularly stabilized helical structure similar to the crystal structure of the homologous avian pancreatic polypeptide (APP).

Rapid purification and revised amino-terminal sequence of hirudin: a specific thrombin inhibitor of the bloodsucking leech

Hirudin is a specific polypeptide thrombin inhibitor consisting of 65 amino acids that is produced by the leech, Hirudo medicinalis. We describe a rapid method for the purification of hirudin from a leech extract. Crude hirudin, purchased from a commercial source, was first fractionated on a DEAE-HPLC column using a salt gradient. Hirudin activity was monitored by inhibition of the thrombin-mediated hydrolysis of a synthetic substrate H-D-Phenylalanyl-Pipecolyl-Arginine-p-Nitroanilide. The fractions containing antithrombin activity were pooled and further purified by reverse-phase HPLC. The homogeneity of purified hirudin was confirmed by a single amino-terminal sequence for 43 residues with Val-Val as the first two amino acids. Residue 33 was Asn rather than Asp as reported previously.

Antithrombin properties of C-terminus of hirudin using synthetic unsulfated N alpha-acetyl-hirudin45-65

Unsulfated N alpha-acetyl-hirudin45-65 (MDL 27 589), which corresponds to the C-terminus of hirudin1-65, was synthesized by solid-phase methods. The synthetic peptide was able to inhibit fibrin formation and the release of fibrinopeptide A from fibrinogen by thrombin. The catalytic site of thrombin was not perturbed by the synthetic peptide as H-D-Phe-Pip-Arg-pNA hydrolysis (amidase activity) was not affected. The binding of synthetic peptide and thrombin was assessed by isolation of the complex on gel-filtration chromatography. A single binding site with a binding affinity (Ka) of approx. 1.0 X 10(5) M-1 was observed for thrombin-hirudin45-65 interaction. The data suggest that the C-terminal residues 45-65 of hirudin contain a binding domain which recognizes thrombin and yet does not bind to the catalytic site of the enzyme.