Protein inhibitors of trypsin from the seeds of Cucurbitaceae plants

Seven trypsin inhibitors were isolated from the seeds of Cucurbitaceae plants: two from cucumber (Cucumis sativus) and red bryony (Bryonia diotica) and one from figleaf gourd (Cucurbita ficifolia), spaghetti squash (Cucurbita pepo var. (vegetable spaghetti) and water melon (Citrullus vulgaris). The inhibitors were purified by fractionation with ammonium sulphate, followed by ion-exchange chromatography and affinity chromatography using immobilized trypsin or anhydro-trypsin. The homogeneous inhibitors from cucumber and water melon are made up of 32 and 30 amino acid residues, respectively, whereas the remaining ones of 29 residues. All inhibitors contain three disulphide bridges and are free of threonine, phenylalanine and tryptophan. Inhibitors from spaghetti squash and CSTI IIb from cucumber are inactivated by acetylation of free amino groups whereas the remaining ones are inactivated by modification of arginine with 1,2-cyclohexanedione. Thus the P1 residues of the reactive sites of the inhibitors are lysine and arginine, respectively.     

The squash family of serine proteinase inhibitors. Amino acid sequences and association equilibrium constants of inhibitors from squash, summer squash, zucchini, and cucumber seeds

Six amino acid sequences for trypsin inhibitors isolated from squash, summer squash, zucchini, and cucumber seeds were determined. All these inhibitors along with the two previously sequenced squash inhibitors (1) form the squash inhibitor family. The striking characteristic of the family is that its member inhibitors are very small (29-32 residues, 3 disulfide bridges). The association equilibrium constants with bovine beta trypsin for 6 squash family inhibitors were determined and range from 5.9 X 10(10) to 9.5 X 10(11) M-1.     

Trypsin inhibitors in summer squash (Cucurbita pepo) seeds. Isolation, purification and partial characterization of three inhibitors

Three trypsin inhibitors were isolated from summer squash (Cucurbita pepo) seeds and purified to homogeneity by fractionation with ammonium sulphate and methanol, ion-exchange chromatography and gel filtration. All three inhibitors have lysine at their active site. Two of them (II, IV) show the same isoelectric point (at pH 5.6), amino acid composition and molecular mass (3259). The third inhibitor (III) of molecular mass of 3654 and isoelectric point at 4.9 has additionally one histidine residue and two glutamic acid residues more per molecule.     

Globulin-specific Proteolytic Activity in Germinating Pumpkin Seeds as Detected by a Fluorescence Assay Method

The proteolytic activities of α-chymotrypsin, trypsin, pepsin, bromelain, and an extract from germinating pumpkin seeds (Cucurbita moschata) were determined by their ability to effect the release of 1-anilino-8-naphthalenesulfonate bound to internal hydrophobic sites in intact protein substrates. Casein, glyceraldehyde-3-P dehydrogenase, urease, catalase, pumpkin seed globulin, and bovine serum albumin enhanced the fluorescence of 1-anilino-8-naphthalenesulfonate sufficiently to be used as proteolytic substrates. Chymotrypsin, trypsin, pepsin, and bromelain exhibited activity against all or almost all of the protein substrates. The activity of 1 μg of α-chymotrypsin or trypsin and 100 ng of pepsin could be easily detected by this method of assay within 4 to 5 minutes depending upon the substrate. The enzyme extracted from 3-day germinated pumpkin seeds exhibited strong activity only against pumpkin seed globulin, weak activity against the globulins of squash and cucumber and casein, and no activity against the other protein substrates. Activity against pumpkin globulin was maximal at pH 7.4. When assayed by an increase in ninhydrin-positive products, the enzyme extract from pumpkin seeds also showed strong activity against pumpkin globulin and weak activity against casein. The 1-anilino-8-naphthalenesulfonate-fluorescence method was at least 20 times more sensitive than the ninhydrin method and was 10 to 20 times more rapid.     

嫁接黄瓜地上部的南瓜根系分泌物对种子萌发的影响

经嫁接黄瓜接穗的南瓜根系分泌物对黄瓜和南瓜的发芽率和胚根、胚轴的伸长均具有明显的抑制作用.分析表明:嫁接黄瓜根系分泌物可以促进黄瓜和南瓜体内吲哚乙酸氧化酶的活性,抑制淀粉酶的活性,从而降低其吲哚乙酸(IAA)水平,影响子叶中贮藏物质的转化和利用,抑制其萌发和生长.     

Serine proteinase from Cucurbita ficifolia seed; purification, properties, substrate specificity and action on native squash trypsin inhibitor (CMTI I)

A proteinase was purified from resting seeds of Cucurbita ficifolia by ammonium sulfate fractionation and successive chromatography on CM-cellulose, Sephacryl S-300 and TSK DEAE-2SW (HPLC) columns. Inhibition by DFP and PMSF suggests that the enzyme is a serine proteinase. The apparent molecular mass of this enzyme is ca. 77 kDa. The optimum activity for hydrolysis of casein and Suc-Ala-Ala-Pro-Phe-pNA is around pH 10.5. The following peptide bonds in the oxidized insulin B-chain were hydrolysed by the proteinase: Phe1-Val2, Asn3-Gln4, Gln4-His5, Cya7-Gly8, Glu13-Ala14, Ala14-Leu15, Cya19-Gly20, Pro28-Lys29 and Lys29-Ala30. The proteinase is more selective towards the native squash seed trypsin inhibitor (CMTI I) and primarily cuts off only its N-terminal arginine. The inhibitor devoided of the N-terminal arginine residue is still active against trypsin.     

Isolation of a trypsin inhibitor with deletion of N-terminal pentapeptide from the seeds of Momordica cochinchinensis, the Chinese drug mubiezhi.

A trypsin inhibitor, MCCTI-1, with a molecular weight of 3479 Da as determined by mass spectrometry, was isolated from Momordica cochinchinensis seeds with a procedure involving extraction with 5% acetic acid, ammonium sulfate precipitation, ion exchange chromatography on CM-Sepharose and reverse-phase high performance liquid chromatography. The sequence of its first 13 N-terminal amino acid residues was ILKKCRRDSDCPG which was about 85% identical with the sequence of trypsin inhibitor MCTI-1 from Momordica charantia Linn. When compared with the sequences of most other squash family trypsin inhibitors, the sequence of MCCTI-1 was characterized by the deletion of a pentapeptide from the N-terminus. Trypsin inhibitors also existed in seeds of some hitherto uninvestigated Cucurbitaceae species.     

1H NMR spectra of trypsin inhibitors from seeds of Cucurbitaceae plants. Resonance signals of methyl groups

1H NMR spectra (250 MHz) of four trypsin inhibitors isolated from seeds of Cucurbitaceae plants were studied. It was found that structural differences between the inhibitors from the genus Cucurbita and from the genus Cucumis consist, among others, in the presence in the former group of a valine residue strongly shielded from the solvent.     

Purification and characterization of proteinase inhibitors from adzuki beans (Phaseolus angularis).

Two proteinase inhibitors, designated as inhibitors I and II, were purified from adzuki beans (Phaseolus angularis) by chromatographies on DEAE- and CM-cellulose, and gel filtration on a Sephadex G-100 column. Each inhibitor shows unique inhibitory activities. Inhibitor I was a powerful inhibitor of trypsin [EC 3.4.21.4], but essentially not of chymotrypsin ]EC 3.4.21.1]. On the other hand, inhibitor II inhibited chymotrypsin more strongly than trypsin. The molecular weights estimated from the enzyme inhibition were 3,750 and 9,700 for inhibitors I and II, respectively, assuming that the inhibitions were stoichiometric and in 1 : 1 molar ratio. The amino acid compositions of both inhibitors closely resemble those of low molecular weight inhibitors of other leguminous seeds: they contain large amounts of half-cystine, aspartic acid and serine, and little or no hydrophobic and aromatic amino acids. Inhibitor I lacks both tyrosine and tryptophan residues. The molecular weights were calculated to be 7,894 and 8,620 for inhibitors I and II, respectively. The reliability of these molecular weights was confirmed by the sedimentation equilibrium and 6 M guanidine gel filtration methods. On comparison with the values obtained from enzyme inhibition, it was concluded that inhibitor I and two trypsin inhibitory sites on the molecule, whereas inhibitor II had one chymotrypsin and one trypsin inhibitory sites on the molecule.     

A crystalline protein-proteinase inhibitor from pinto bean seeds.

A crystalline protein-proteinase inhibitor has been isolated from seeds of Pinto bean (Phaseolus vulgaris cultvar. Pinto). It has an average molecular weight of 19 000 as estimated by gel filtration. This crystalline inhibitor is highly active against both bovine pancreatic trypsin and alpha-chymotrypsin. Complexes of both trypsin-inhibitor and alpha-chymotrypsin-inhibitor have been isolated. The inhibitor which was derived from the dissociated trypsin-inhibitor complex was only 62% as effective as the original compound against either enzyme. In contrast, the inhibitor obtained from alpha-chymotrypsin-inhibitor complex retained its full original inhibitory activity for trypsin, but only 25% of its original activity against alpha-chymotrypsin. The dissociated inhibitor from alpha-chymotrypsin-inhibitor compex, despite its full inhibitory activity, had been modified to such an extent that it could no longer form any precipitable complex with trypsin. The crystalline protein-proteinase inhibitor is not homogeneous and has been resolved into two distinct inhibitors in terms of their physical and chemical properties. These two inhibitors are designated as Pinto bean proteinase inhibitor I and II and their respective minimum molecular weights are 9100 and 10 000. They differ most strikingly in their amino acid composition in that inhibitor II is void of both valine and methionine.     

Inhibition of human beta-factor XIIa by squash family serine proteinase inhibitors

Many inhibitors of trypsin and human beta-factor XIIa have been isolated from squash and related seeds and sequenced (Wieczorek et al., Biochem. Biophys. Res. Comm. (1985) 126, 646-652). The association equilibrium constants (Ka) of several of these inhibitors have now been determined with human beta-factor XIIa using a modification of the method of Green and Work (Park et al., Fed. Proc. Fed. Am. Soc. Exp. Biol. (1984) 43, 1962). The Ka's range from 7.8 x 10(4) M-1 to 3.3 x 10(8) M-1. Two isoinhibitors from Cucurbita maxima seeds, CMTI-I and CMTI-III, differ in only a single glutamate to lysine change in the P'4 position. This results in a factor of 62 increase in the Ka of the lysine inhibitor, CMTI-III (Ka = 3.3 x 10(8) M-1). To our knowledge, this is the largest effect ever seen for a residue substitution at the P'4 position of a serine proteinase inhibitor. The result is even more surprising because beta-factor XIIa's natural substrate, Factor XI, contains Gly in the P'4 position.     

Isolation and partial amino acid sequence of the trypsin inhibitor from the seeds of Cucurbita maxima

Trypsin inhibitor from squash (Cucurbita maxima) seed was extracted with 0.1 M-acetate buffer, pH 4.5, purified on immobilized trypsin, and separated by SE-Sephadex C-50 chromatography into three active fractions. All of them inhibited trypsin to the same extent, showed no antichymotrypsin or antikallikrein activity, had a similar molecular weight (about 3300), and contained no tryptophan, phenylalanine or threonine. The partial amino acid sequence of tryptic and peptic peptides of fraction III was determined by Edman degradation procedure.     

Heterogeneity of the basic pancreatic inhibitor (Kunitz) in various bovine organs

Four protein protease inhibitors (I, II, III, IV) having low molecular weights (10 600-6500) and basic isoelectric points were isolated by affinity chromatography from bovine spleen. Inhibitor IV was identified as the basic pancreatic trypsin inhibitor (Kunitz inhibitor); the presence and distribution of components I, II and III vary in the different bovine organs. Spleen inhibitors I, II, III and IV were purified by ion-exchange chromatography; they form 1:1 complexes with trypsin and inhibit enzymatic activity of trypsin, chymotrypsin and kallikrein. Inhibitors I, II and III contain carbohydrate moieties (7-4%) covalently bound to the polypeptide chain. Specific basic pancreatic trypsin inhibitor antiserum has shown the complete identity between inhibitor IV and the basic pancreatic trypsin inhibitor, while partial cross-reactivity between the basic pancreatic trypsin inhibitor and inhibitors I, II and III can be seen from a double immunodiffusion test.     

Determination of the complete three-dimensional structure of the trypsin inhibitor from squash seeds in aqueous solution by nuclear magnetic resonance and a combination of distance geometry and dynamical simulated annealing

The complete three-dimensional structure of the trypsin inhibitor from seeds of the squash Cucurbita maxima in aqueous solution was determined on the basis of 324 interproton distance constraints, 80 non-nuclear Overhauser effect distances, and 22 hydrogen-bonding constraints, supplemented by 27 phi backbone angle constraints derived from nuclear magnetic resonance measurements. The nuclear magnetic resonance input data were converted to the distance constraints in a semiquantitative manner after a sequence specific assignment of 1H spectra was obtained using two-dimensional nuclear magnetic resonance techniques. Stereospecific assignments were obtained for 17 of the 48 prochiral centers of the squash trypsin inhibitor using the floating chirality assignment introduced at the dynamical simulated annealing stage of the calculations. A total of 34 structures calculated by a hybrid distance geometry-dynamical simulated annealing method exhibit well-defined positions for both backbone and side-chain atoms. The average atomic root-mean-square difference between the individual structures and the minimized mean structure is 0.35(+/- 0.08) A for the backbone atoms and 0.89(+/- 0.17) A for all heavy atoms. The precision of the structure determination is discussed and correlated to the experimental input data.     

Protease inhibitors from Ecballium elaterium seeds

Several protease inhibitors were found in the seeds of a Cucurbitacea, Ecballium elaterium, and were separated from one another by affinity and molecular sieve chromatography. Three main trypsin isoinhibitors were purified by ion-exchange chromatography and the sequence of the major one, EETI II, was elucidated and compared with other inhibitors of the squash family. It is a peptide of M.W. 3020 of strong inhibitory activity (Ka = 8 x 10(11) M-1) against trypsin, showing high Gly content, six half-cystine residues, but devoid of histidine, threonine, tryptophan, and tyrosine residues.     

Purification and Properties of the Trypsin Inhibitors from Buckwheat Seed

The trypsin inhibitors in buckwheat seeds were isolated by affinity chromatography on trypsin-Sepharose 4B, and the components were fractionated by chromatography on DEAE-Sepharose CL-6B. The major components, inhibitors I, II and III, were found to be homogeneous proteins with molecular weight of about 8,000. Trypsin inhibitory activity was more pronounced than the chymotrypsin inhibitory activity in all the inhibitor preparation obtained. The three major inhibitors had similar amino acid compositions and had no detectable amounts of tryptophan and carbohydrate. A high level of acidic and basic amino acid residues and a low level of methionine, tyrosine and phenylalanine residues characterized the inhibitors. Although the inhibitors I and II were particularly thermostable, inhibitor III, the most abundant component, was shown to be relatively heat-labile.     

Nuclear magnetic resonance solution and X-ray structures of squash trypsin inhibitor exhibit the same conformation of the proteinase binding loop

A comparison of the solution nuclear magnetic resonance (n.m.r.) structures of squash trypsin inhibitor from seeds of the squash Cucurbita maxima with the X-ray structure of a trypsin complex of the inhibitor shows that the n.m.r. and X-ray structures are similar in terms of the global folding and secondary structure. The average atomic root-mean-square difference between the 36 n.m.r. structures on the one hand and the X-ray structure is 0.96 A for the backbone atoms and 1.95 A for all heavy atoms. The n.m.r. and X-ray structures exhibit extremely similar conformations of the primary proteinase binding loop. Despite the overall similarity, there are small differences between the mean computed structure and the X-ray structure. The n.m.r. structures have slightly different positions of the segments from residues 16 to 18, and 24 and 25. The n.m.r. results show that the inclusion of stereospecific assignments and precise distance constraints results in a significant improvement in the definition of the n.m.r. structure, making possible a detailed analysis of the local conformations in the protein.     

Purification and characterization of the trypsin inhibitor from Cucurbita pepo var. patissonina fruits

Three trypsin inhibitor fractions were found in white bush fruits (Cucurbita pepo L. var. patissonina). One of them, CPPTI-fIII, was purified to homogeneity by means of affinity and ion exchange chromatography. It is a cysteine-poor protein with an approximate Mr of 21 000. The inhibitor contains arginine at position P1 of the reactive site and inhibits bovine trypsin, hog pancreatic kallikrein and subtilisin. This inhibitor differs from the inhibitors of white bush dormant seeds, CPPTI-I and CPPTI-II, in its amino-acid composition, molecular mass, amino-acid residue at position P1 of the reactive site and inhibition spectrum.     

Amino acid sequencing of a trypsin inhibitor by refined 1.6 A X-ray crystal structure of its complex with porcine beta-trypsin.

The stoichiometric complex formed between porcine beta-trypsin and the Momordica charantia, Linn. Cucurbitaceae trypsin inhibitor-A (MCTI-A) was crystallized and its X-ray crystal structure determined using molecular replacement method. The primary sequence and topology of the inhibitor was determined by recognizing the electron density and refined to a final R value of 0.167 (7.0-1.6 A) with RMS deviation of bond lengths from standard values 0.012 A. The sequence was compared with those obtained by other groups and was found to be similar to the squash proteinase inhibitor. Its spatial structure and the conformation of its primary binding segment from Cys-3I (P3) to Glu-7I (P3') which contains the reactive scissile bond Arg-5I C-Ile-6I N were also very similar with other squash family proteinase inhibitors.