Studies on trypsin inhibitors. Part I. Synthesis of protected peptides related to sequence 1-10 of porcine pancreatic secretory trypsin inhibitor II (Kazal).

The general strategy for the synthesis, by conventional procedures, of the entire sequence of porcine pancreatic secretory trypsin inhibitor II (Kazal) is discussed. The synthesis of two protected peptides corresponding to positions 2-10 and 1-10 of the proposed primary structure of the inhibitor is described. The heptapeptide free base threonyl-S-acetamidomethylcysteinylthreonylseryl-gamma-tert-butylglutamylvalylserine tert-butyloxycarbonylhydrazide (sequence 4-10) was acylated, by the azide procedure, with either the dipeptide benzyloxycarbonyl-gamma-tert-butylglutamylalanine hydrazide (sequence 2-3) or the tripeptide Nalpha-benzyloxycarbonyl-Nomega-nitroarginylglutamylala-nine hydrazide (sequence 1-3). The stereochemical homogeneity of the resulting peptides, benzyloxycarbonyl-gamma-tert-butylglutamylalanylthreonyl-S-acetamidomethyl-cysteinylthreonylseryl-gamma-tert-butylglutamylvalylserine tert-butyloxycarbonylhydrazide and Nalpha-benzyloxycarbonyl-Nomega-nitroarginylglutamylalanylthreonyl-S-acetamido-methylcysteinylthreonylseryl-gamma-tert-butylglutamylvalylserine tert-butyloxycarbonyl-hydrazide, was assessed, after partial deprotection with liquid hydrogen fluoride, by digestion with aminopeptidase M followed by quantitative amino acid analysis.     

Studies on trypsin inhibitors. Part IX. Synthesis and trypsin inhibitory activity of the duopentacontapeptide corresponding to the amino acid sequence of porcine pancreatic secretory trypsin inhibitor II (Kazal).

The synthesis of the protected duopentacontapeptide corresponding to the entire amino acid sequence I-52 of porcine pancreatic secretory trypsin inhibitor II (Kazal type) is described. The benzyloxycarbonyltetradecapeptide tert-butyloxycarbonylhydrazide (sequence 1-14) was selectively deblocked with trifluoroacetic acid and used to acylate, by the azide procedure, the peptide free base corresponding to the sequence 15-52. The isolated material was purified by ion exchange chromatography and the protecting groups were removed by successive treatments with anhydrous hydrogen fluoride, 1 M piperidine and mercuric acetate. F02M phosphate buffer, pH8. Determination of the inhibitory capacity indicated that the synthetic material is about 50% effective, at 30:1 inhibitor:trypsin molar ratio in inhibiting the tryptic hydrolysis of Nalpha-benzoyl-DL-arginine-4-nitroanilide. Full inhibition was achieved at a higher inhibitor:trypsin molar ratio. The stability constants and the standard free energy of binding of the complex between trypsin and the synthetic inhibitor have been determined.     

Studies on trypsin inhbitors. Part II. Synthesis of the protected tetrapeptide (sequence 11-14) of porcine pancreatic secretory trypsin inhibitor II (Kazal).

Synthesis is described of the protected tetrapeptide corresponding to positions 11-14 of the primary structure of the porcine pancreatic secretory trypsin inhibitor II (Kazal), in the form of free acid as well as protected hydrazide. The tetrapeptide tert-butyloxycarbonylglycyl-S-acetamidomethylcysteinylprolyl-Nepsilon-trifluoroacetyl-lysine was prepared by stepwise elongation from the C-terminal Nepsilon-trifluoroacetyllysine using successively 1-succinimidyl benzyloxycarbonylprolinate, p-nitrophenyl N-tert-butyloxycarbonyl-S-acetamidomethylcysteinate and 1-phenyl-3-methyl-4-(tert-butyloxycarbonylglycyl)-oximinyl-5-(benzyloxycarbonylglycyl)-imino-2-pyrazoline as acylating agents. Alternately, the dipeptide benzyloxycarbonylprolyl-Nepsilon-trifluoroacetyllsine was transformed into the corresponding tert-butyloxycarbonylhydrazide which was reacted, after catalytic hydrogenolysis, with tritylglycyl-S-acetamido-methylcysteine to give the tetrapeptide tritylglycyl-S-acetamidomethylcysteinylprolyl-Nepsilon-trifluoroacetyllsine tert-butyloxycarbonylhydrazide. The stereochemical homogeneity of the final products was assessed, after partial deprotection with aqueous 90% trifluoroacetic acid, by digestion with papain and aminopeptidase M, followed by quantitative amino acid analysis.     

Studies on trypsin inhibitors. Part VIII. Synthesis of the protected octatriacontapeptide corresponding to the sequence 15-52 of porcine pancreatic secretory trypsin inhibitor II (Kazal)

The synthesis by fragment condensation of protected peptides corresponding to the amino acid sequences 15-35, 25-52 and 15-52 of porcine pancreatic secretory trypsin inhibitor II (Kazal type) is described. The Rudinger modification of the azide procedure was used in the fragment coupling steps. The tert-butyloxycarbonylheptapeptide hydrazide (sequence 22-28) was reacted with the heptapeptide methyl ester free base (sequence 29-35) and the resulting tert-butyloxycarbonyltetradecapeptide methyl ester after selective deprotection, coupled with the benzyloxycarbonylheptapeptide hydrazide (sequence 15-21) to give the protected peptide methyl ester corresponding to the 15-35 sequence which was then converted to the corresponding hydrazide. The synthesis of the 25-52 sequence was achieved by assembling the protected peptide hydrazide corresponding to the amino acid residues 25-35, with the C-terminal heptadecapeptide 36-52. The resulting protected octaeicosapeptide (sequence 25-52) was selectively deblocked with trifluoroacetic acid and acylated with the benzyloxycarbonyldecapeptide hydrazide 15-24 to give the desired octatriacontapeptide corresponding to sequence 15-52 of the inhibitor. An attempt to prepare the 15-52 sequence through the condensation of fragments corresponding to 15-35 and 36-52 sequences was unsuccessful. The identity and purity of the synthetized peptide derivatives wre established by elemental analysis (in some cases), amino acid analysis, optical rotation, and thin-layer chromatography in two solvent systems. The final products were also evaluated, after partial deprotection with anhydrous hydrogen fluoride or aqueous 90% trifluoroacetic acid, by paper electrophoresis at different pH values.     

Studies on trypsin inhibitors. Part IV, Synthesis of the protected undecapeptide (sequence 25-35) of porcine pancreatic secretory trypsin inhibitor II (Kazal).

Synthesis is described of the protected undecapeptide tert-butyloxycarbonylisoleucyl-threonyltyrosylserylasparaginyl-gamma-tert-butylglutamyl-S-acetamidomethylcysteinyl-valylleucyl-S-acetamidomethylcysteinylseriny hydrazide corresponding to positions 25-35 of the amino acid sequence of porcine pancreatic secretory trypsin inhibitor II (Kazal). The hepatapeptide free base methyl asparaginyl-gamma-tert-butylglutamyl-S-acetamidomethylcysteinylvalylleucyl-S-acetamidomethylcysteinylserinate (sequency 29-35) was acylated, by the azide procedure, with the tetrapeptide tert-butyloxycarbonl-isoleucylthreonyltyrosylserine hydrazide /sequence 25-28) and the resulting tert-butyloxycarbonylundecapeptide methyl ester was transformed into the corresponding hydrazide by hydrazinolysis. The stereochemical homogeneity of the final product was assessed, after partial deprotection with aqueous 90% trifuoroacetic acid, by digestion with papain and aminopeptidase M followed by quantitative amino acid analysis.     

Studies on trypsin inhibitors. Part VI. Synthesis of the protected nonapeptide (sequence 44-52) of porcine pancreatic secretory trypsin inhibitor II (Kazal).

Synthesis is described of the partially protected nonapeptide tert-butyloxycarbonyl-valylleucylisoleucylglutaminyl-N-trifluoroacetyllsylserylglycylprolyl-S-acetamido-methylcysteine corresponding to positions 44-52 of the amino acid sequence of porcine pancreatic secretory trypsin inhibitor II. The hexapeptide free base glutaminyl-N-trifluoroacetyllsylserylglycylprolyl-S-acetamidomethylcysteine, prepared by two alternative routes, was acylated by the azide procedure, with the tripeptide tert-butyloxycarbonylvalylleucylisoleucine hydrazide. The stereochemical homogeneity of the resulting nonapeptide was assessed, after partial deprotection by treatment with aqueous 90% trifluoroacetic acid, by digestion with papain and aminopeptidase M followed by quantitative amino acid analysis.     

Studies on trypsin inhibitors. Part V. Synthesis of the protected octapeptide (sequence 36-43) of porcine pancreatic secretory trypsin inhibitor II (Kazal).

Synthesis is described of the partially protected octapeptide tert-butyloxycarbonyl-gamma-tert-butylglutamylasparaginyl-N-trifluoroacetyllysyl-N-trifluoracetyllysylarginyl-Ngamma-4,4'-dimethoxybenzhydryglutaminylthreonylproline corresponding to positions 36-43 of the amino acid sequence of porcine pancreatic secretory trypsin inhibitor II. The tetrapeptide free base arginyl-Ngamma-4,4'-dimethoxybenzhydrylglutaminylthreonylproline was acylated, by the azide proceedure, with the tripeptide benzyloxycarbonyl-asparaginyl-N-trifluoroacetyllsyl-N-trifluoroacetyllysine hydrazide. The resulting protected heptapeptide was partially deblocked by catalytic hydrogenation and reacted with alpha-1-succinimidyl-gamma-tert-butyl tert-butyloxycarbonylglutamate. The stereochemical homogeneity of the ensuing octapeptide was assessed, after partial deprotection with aqueous 90% trifluoroacetic acid, by digestion with papain and aminopeptidase M followed by quantitative amino acid analysis.     

Studies on peptides. CXXVIII. Application of new heterobifunctional crosslinking reagents for the preparation of neurokinin (A and B)-BSA (bovine serum albumin) conjugates

A decapeptide corresponding to the entire amino acid sequence of neurokinin A, a porcine spinal cord peptide, was synthesized in a conventional manner using protecting groups removable by 1 M TFMSA-thioanisole in TFA. The HS-CH2CH2CO group was introduced onto the synthetic neurokinin A by reaction of 3-(S-acetyl-thiopropionyl)-thiazolidine-2-thione, followed by deacetylation with hydroxylamine. 2,4-Dinitrophenyl-p-(beta-nitrovinyl)-benzoate trapped the above HS-CH2CH2CO-neurokinin A derivative in acidic media, then BSA in basic media in nearly quantitative yield. A similar decapeptide, neurokinin B, was also synthesized and conjugated onto BSA using an alternative SH-introducing reagent, 3-(S-p-methoxybenzyl-thiopropionyl)-thiazolidine-2-thione, and the above heterobifunctional conjugating reagent.     

Characterization of a trypsin inhibitor from equine urine.

A trypsin inhibitor was isolated from pregnant mares' urine by adsorption on bentonite and elution with aqueous pyridine followed by batch DEAE-cellulose treatment and column chromatography. Final purification to an electrophoretically homogenous glycoprotein was achieved by gel permeation chromatography. This equine urinary trypsin inhibitor (E-UTI) is acid- and heat-stable, has a molecular weight of 22 to 23 kDa, an isoelectric point of 4.55, forms a 1:1 molar complex with trypsin and has serine as its N-terminal amino acid. The N-terminal amino acid sequence of this protein is almost identical with that of EI-14, the inhibitor obtained from horse serum by tryptic treatment, except for two extra amino acid residues, Ser-Lys- on the N-terminal end of E-UTI. In its isoelectric point E-UTI differs from EI-14 and the inhibitor from human urine.     

Synthesis and 13C-NMR spectra of the N-terminal decapeptide sequence of human lymphoblast interferon

The N-terminal sequence 1-10 of interferon HuIFN-alpha(Ly) from human lymphoblasts Ser-Asp-Leu-Pro-Gln-Thr-His-Ser-Leu-Gly (LIF[1-10]) was synthesized by the Merrifield method. N-tert-Butyloxycarbonylglycin was esterified via its cesium salt with a chloro-methylated polystyrene-1% divinylbenzene support yielding a loading of 0.3 mmol/g. Double couplings, each with a five-fold excess of N-protected amino acid, were performed with N,N'-dicyclohexylcarbodiimide and 1-hydroxybenzotriazole, followed by an acetylation step. N-tert-Butyloxycarbonyl-L-amino acids with O-benzyl protection for serine, threonine, and Nim-2,4-dinitrophenyl protection for histidine, and N-fluorenylmethyloxycarbonylaspartic acid beta-tert-butyl ester were used. N-tert-Butyloxycarbonyl-glutamine was coupled as 4-nitrophenyl ester in the presence of 1-hydroxybenzotriazole. The butyloxycarbonyl groups of the residues 3 to 10 were removed with trifluoroacetic acid in dichloromethane; the 9-fluorenylmethyloxycarbonyl group was split off with diethylamine. After quantitative hydrazinolysis in dimethylformamide, chromatography on Sephadex LH-20 with methanol and reversed-phase chromatography on silica gel RP-8 with methanol/water 9:1, the decapeptide hydrazide Boc-Ser(Bzl)-Asp(But)-Leu-Pro-Gln-Thr(Bzl)-His-Ser(Bzl)-Leu-Gly-NH-HN2 was isolated in pure state. The partially protected decapeptide was characterized by 13C-NMR spectroscopy, analysed, and linked with poly(L-lysine) (molecular mass 37 300) via its azide and also using m-xylylene diisocyanate. After a deprotection step the polylysine-LIF[1-10] antigens were dialyzed and lyophilized. Furthermore the free decapeptide LIF[1-10] was split-off from the resin using HBr/CF3CO2H, followed by mercaptoethanol treatment. After purification on Sephadex G-15 with 0.1 M acetic acid and on the reversed-phase silicagel RP-8 with methanol/water 9:1 water soluble LIF-[1-10] was obtained in pure state as shown by thin-layer-chromatography, electrophoreses amino acid analysis and 13C-NMR spectroscopy.     

The complete amino acid sequence of barley trypsin inhibitor

The amino acid sequence of barley trypsin inhibitor has been determined. The protein is a single polypeptide consisting of 121 amino acid residues and has Mr = 13,305. No free sulfhydryl groups were detected by Ellman's reagent, which indicates the presence of five disulfide bridges in the molecule. The primary site of interaction with trypsin was tentatively assigned to the arginyl-leucyl residues at positions 33 and 34. On comparison of the sequence of this inhibitor with those of other proteinase inhibitors, we found that the barley trypsin inhibitor could not be classified into any of the established families of proteinase inhibitors (Laskowski, M., Jr., and Kato, I. (1980) Annu. Rev. Biochem. 49, 593-626) and that this inhibitor should represent a new inhibitor family. On the other hand, this trypsin inhibitor showed a considerable similarity to wheat alpha-amylase inhibitor (Kashlan, N., and Richardson, M. (1981) Phytochemistry (Oxf.) 20, 1781-1784) throughout the whole sequence, suggesting a common ancestry for both proteins. This is the first case of a possible evolutionary relationship between two inhibitors directed to totally different enzymes, a proteinase and a glycosidase.     

Purification and characterization of a trypsin inhibitor from Solanum tuberosum.

A trypsin inhibitor isolated from a potato acetone powder has been purified by affinity chromatography. This protein inhibits trypsin mole per mole. To a lesser extent it combines also with chymotrypsin and elastase. For trypsin, K1 = 8 X 10(-7) M. The inhibitor has a single polypeptide chain of 207 amino acid residues. It contains no sugar or free sulfhydryl groups. Its extinction coefficient E2801% = 10.3 and its isoelectric point is 6.9. Its molecular weight is of the order of 21 000-22000, as determined by sedimentation equilbrium, by inhibition experiment or from its amino acid composition. These same techniques, taken together with the single band observed at different pH on polyacrylamide gel electrophoresis, indicate that the protein purified is monodisperse. However, the finding of two N-terminal amino acid residues, leucine and aspartic acid, and the different stoichometry observed during the interaction of the inhibitor, either with trypsin or with chymotrypsin and elastase, raises the possibility that our preparation is contaminated by a polyvalent inhibitor not detectable by physiochemical methods.     

Amino acid sequences of two trypsin inhibitors from winged bean seeds (Psophocarpus tetragonolobus (L)DC.)

The trypsin inhibitor (WTI-1) purified from winged bean seeds is a Kunitz type protease inhibitor having a molecular weight of 19,200. WTI-1 inhibits bovine trypsin stoichiometrically, but not bovine alpha-chymotrypsin. The approximate Ki value for the trypsin-inhibitor complex is 2.5 X 10(-9) M. The complete amino acid sequence of WTI-1 was determined by conventional methods. Comparison of the sequence with that of soybean trypsin inhibitor (STI) indicated that the sequence of WTI-1 had 50% homology with that of STI. WTI-1 was separated into 2 homologous inhibitors, WTI-1A and WTI-1B, by isoelectric focusing. The isoelectric points of WTI-1A and WTI-1B were 8.5 and 9.4, respectively, and their sequences were presumed from their amino acid compositions.     

A Kazal-type trypsin inhibitor from the protochordate Ciona intestinalis.

A trypsin inhibitor from Ciona intestinalis, present throughout the animal, was purified by ion-exchange chromatography followed by four HPLC steps. By MS the molecular mass of the native form was determined to be 6675 Da. The N-terminal amino acid sequence was determined by protein sequencing, but appeared to be partial because the theoretical molecular mass of the protein was 1101 Da too low. Thermolysin treatment gave rise to several fragments each containing a single disulphide bridge. By sequence analysis and MS intramolecular disulphide bridges could unequivocally be assigned to connect the pairs Cys4-Cys37, Cys8-Cys30 and Cys16-Cys51. The structure of the inhibitor is homologous to Kazal-type trypsin inhibitors. The inhibitor constant, KI, for trypsin inhibition was 0.05 nM whereas chymotrypsin and elastase were not inhibited. To reveal the complete sequence the cDNA encoding the trypsin inhibitor was isolated. This cDNA of 454 bp predicts a protein of 82 amino acid residues including a 20 amino acid signal peptide. Moreover, the cDNA predicts a C-terminal extension of 11 amino acids compared to the part identified by protein sequencing. The molecular mass calculated for this predicted protein is in accordance with the measured value. This C-terminal sequence is unusual for Kazal-type trypsin inhibitors and has apparently been lost early in evolution. The high degree of conservation around the active site strongly supports the importance of the Kazal-type inhibitors.     

The trypsin and chymotrypsin inhibitors in chick peas (Cicer arietinum L). Identification of the trypsin-reactive site, partial-amino-acid sequence and further physico-chemical properties of the major inhibitor.

The two principal isoinhibitors P-5 and P-6 isolated earlier from the seeds of chick peas (Cicer arietinum L.) by a procedure involving biospecific affinity chromatography on active, matrix-bound trypsin are shown to be the virgin and trypsin-modified forms of the same inhibitor. The virgin inhibitor P-5 consists of a single peptide chain of 66 amino acid residues cross-linked by seven disulfide bridges. Upon interaction with the matrix-bound trypsin under the conditions used the virgin inhibitor P-5 is about 50% converted to P-6 by cleavage of a single Lys-Ser linkage at position 14-15 in the molecule. The resulting tetradecapeptide remains bound to the rest of the molecule by two or four disulfide bridges, but the two fragments representing residues 1-14 and 15-66 separate readily by molecular-sieve chromatography following reductive or oxidative cleavage of the disulfide linkages. The sequence 1-25 was established by Edman degradation.     

A possible evolutionary relationship between plant trypsin inhibitor, alpha-amylase inhibitor, and mammalian pancreatic secretory trypsin inhibitor (Kazal)

The amino acid sequence of the carboxyl-terminal half of barley trypsin inhibitor was found to be significantly similar to the whole sequence of bovine pancreatic secretory trypsin inhibitor (Kazal). Kazal type inhibitors and related proteins are known for the extraordinary mode of divergence among animals, and the present observation extends this to a plant for the first time. The present observation together with our previous finding of sequence homology between barley trypsin inhibitor and wheat alpha-amylase inhibitor (Odani, S., Koide, T., & Ono, T. (1982) FEBS Lett. 141, 279-282) suggest an unusual evolutionary relationship between cereal enzyme inhibitors and animal proteinase inhibitors of the Kazal type.     

Isolation and nucleotide sequence of cDNA clone for bovine pancreatic anionic trypsinogen. Structural identity within the trypsin family.

A cDNA clone encoding an anionic form of bovine trypsinogen was isolated from a pancreatic cDNA library. The corresponding 855-nucleotide mRNA contains a short 5' noncoding region of 8 nucleotides and a long 3' noncoding region of 56 nucleotides in addition to a poly(A) tail of at least 50 nucleotides. The deduced amino acid sequence for the anionic pretrypsinogen (247 residues) includes the N-terminal 15-amino-acid signal peptide followed by an 8-amino-acid activation peptide. The zymogen (232 residues) contains an additional C-terminal serine, compared with the amino acid sequence of bovine cationic trypsinogen. The identity between the anionic and cationic forms of bovine trypsinogen (65%) is lower than that existing between the anionic protein and other mammalian anionic trypsinogens (73-85%), suggesting that trypsin gene duplication in mammals occurred prior to the evolutionary events responsible for the species divergence. Bovine pancreatic anionic trypsin possesses all the key amino acids characteristic of the serine protease family.     

Cloning and characterization of a novel trypsin inhibitor (BTIomega1) gene from Fagopyrum esculentum.

Based on the amino acid information of trypsin inhibitor of buckwheat (Fagopyrum Esculentum Moench), degenerated primers were designed and a full-length cDNA sequence named BTIomega1 (Buckwheat Trypsin Inhibitor) was amplified from the leaves RNA by using RT-PCR and rapid amplification of cDNA ends (RACE) methods. Sequence analysis shows that the 392 bp cDNA contained an open reading frame (ORF) of 216 bp, encoding 72 amino acids residues. The deduced amino acid sequence exhibits 96 and 93% homology with BWI-1 and BTI-2, a natural trypsin inhibitor from buckwheat seeds. Southern blotting suggested that three copies of BTIomega1 gene existed in the buckwheat genome. Moreover, a predicted secondary structure and 3D-structural model was constructed by homology modeling. To our knowledge, this is the first all-round report of the gene BTIomega1. The novel BTIomega1 gene has been submitted to the GeneBank under Accession No. DQ289792.     

A synthetic linear decapeptide binds to the atrial natriuretic peptide receptors and demonstrates cyclase activation and vasorelaxant activity

A linear decapeptide, [cyclohexylalanine 106]ANP-(105-114)NH2 (1), where ANP is atrial natriuretic peptide, was prepared by solid phase synthesis and purified by reverse-phase liquid chromatography. This novel peptide was found to bind to ANP receptors in rabbit lung membranes, to stimulate cGMP production in various tissues, and to fully relax precontracted rabbit aorta in a dose-dependent fashion. The potency of 1 in the various in vitro assays varies between one-twentieth and one-eightieth of the potency of the reference peptide, the 24-mer rat ANP-(103-126). The linear decapeptide 1, which encompasses amino acid residues from the rat ANP sequence (105-114), features a cyclohexylalanine residue instead of the phenylalanine 106 residue in the hormone sequence, a free sulfhydryl function at the N-terminal cysteine 105, and a carboxamide C terminus. Its disulfide dimer 6 was active in the rabbit aorta assay while the S-methyl cysteine 7 analogue was not active in the same assay at similar concentrations. The decapeptide 1 is of particular significance because it is the shortest analogue reported to date endowed with agonistic activity at the guanylate cyclase-coupled ANP receptor. In particular, it is interesting to compare its structure to the structures of other short linear analogues of ANP which are totally devoid of the ability to stimulate particulate guanylate cyclase activity.