Positions of disulfide bonds in rye (Secale cereale) seed chitinase-a.

The positions of disulfide bonds of rye seed chitinase-a (RSC-a) were identified by the isolation of disulfide-containing peptides produced with enzymatic and/or chemical cleavages of RSC-a, followed by sequencing them. An unequivocal assignment of disulfide bonds in this enzyme was as follows: Cys3-Cysl8, Cys12-Cys24, Cys15-Cys42, Cys17-Cys31, and Cys35-Cys39 in the chitin-binding domain (CB domain), Cys82-Cys144, Cys156-Cys164, and Cys282-Cys295 in the catalytic domain (Cat domain), and Cys263 was a free form.

Expression and mutational analysis of amino acid residues involved in catalytic activity in a ribonuclease MC1 from the seeds of bitter gourd.

The ribonuclease MC1 (RNase MC1) from seeds of bitter gourd (Momordica charantia) consists of 190 amino acids and belongs to the RNase T2 family, including fungal RNases typified by RNase Rh from Rhizopus niveus. We expressed RNase MC1 in Escherichia coli cells and made use of site-directed mutagenesis to identify essential amino acid residues for catalytic activity. Mutations of His34 and His88 to Ala completely abolished the enzymatic activity, and considerable decreases in the enzymatic activity were observed in cases of mutations of His83, Glu84, and Lys87, when yeast RNA was used as a substrate. Kinetic parameters for the enzymatic activity of the mutants of His83, Glu84, and Lys87 were analyzed using a dinucleoside monophosphate CpU. Km values for the mutants were approximately like that for wild-type, while k(cat) values were decreased by about 6 to 25-fold. These results suggest that His34, His83, Glu84, Lys87, and His88 in RNase MC1 may be involved in the catalytic function. These observation suggests that RNase MC1 from a plant catalyzes RNA degradation in a similar manner to that of fungal RNases.

Crystal structure of a ribonuclease from the seeds of bitter gourd (Momordica charantia) at 1.75 A resolution.

The ribonuclease MC1 (RNase MC1) from seeds of bitter gourd (Momordica charantia) consists of 190 amino acid residues with four disulfide bridges and belongs to the RNase T(2) family, including fungal RNases typified by RNase Rh from Rhizopus niveus and RNase T(2) from Aspergillus oryzae. The crystal structure of RNase MC1 has been determined at 1.75 A resolution with an R-factor of 19.7% using the single isomorphous replacement method. RNase MC1 structurally belongs to the (alpha+beta) class of proteins, having ten helices (six alpha-helices and four 3(10)-helices) and eight beta-strands. When the structures of RNase MC1 and RNase Rh are superposed, the close agreement between the alpha-carbon positions for the total structure is obvious: the root mean square deviations calculated only for structurally related 151 alpha-carbon atoms of RNase MC1 and RNase Rh molecules was 1.76 A. Furthermore, the conformation of the catalytic residues His-46, Glu-105, and His-109 in RNase Rh can be easily superposed with that of the possible catalytic residues His-34, Glu-84, and His-88 in RNase MC1. This observation strongly indicates that RNase MC1 from a plant origin catalyzes RNA degradation in a similar manner as fungal RNases.

Isolation and amino acid sequence of a protein-synthesis inhibitor from the seeds of rye (Secale cereale).

A protein-synthesis inhibitor, designated RPSI, was isolated from the seeds of rye (Secale cereale) using gel filtration and S-Sepharose column chromatography. RPSI is a basic protein with an isoelectric point of over 10, and the concentration of protein required for 50% inhibition of protein synthesis (IC50) of purified RPSI was about ten-fold the concentration of ricin A-chain. The complete amino acid sequence of RPSI was discovered by analyzing the peptides and fragments obtained from the proteolytic digests and by the cyanogen bromide- and hydroxylamine-cleavages of RPSI. RPSI consists of 280 amino acid residues and has a molecular weight of 30,171. RPSI has only 21% sequence identity with that of ricin A-chain, but all five amino acid residues involved in the active site of ricin A-chain are conserved in RPSI.

Chemical modifications of momordin-a and luffin-a, ribosome-inactivating proteins from the seeds of Momordica charantia and Luffa cylindrica: involvement of His140, Tyr165, and Lys231 in the protein-synthesis inhibitory activity.

Effects of chemical modifications on the protein-synthesis inhibitory (PSI) activities of momordin-a and luffin-a were investigated. Treatment with a 50-fold excess of diethylpyrocarbonate at pH 6.5 modified one histidine residue in momordin-a and luffin-a and reduced their PSI activities to 10% and 8.3%, respectively. Modifications with a 20-fold excess of KI3 at pH 7.0 at 0 degree C greatly reduced their PSI activities to 10% by iodination of nearly one tyrosine residue. The PSI activity of momordin-a was rapidly reduced to 6.4% by the modification of one lysine residue with trinitrobenzensulfonic acid as in the case of luffin-a reported previously. By analyses of the tryptic peptides from the modified momordin-a and luffin-a, the modified residues were identified as His140, Tyr165, and Lys231. Furthermore, the amounts of three modified momordin-a binding to rat liver ribosomes were reduced to about half or less than half of that of native momordin-a. From these results, it was suggested that His140, Tyr165, and Lys231 are highly exposed on the surface of momordin-a and luffin-a molecules and are involved in their PSI activities, probably by binding to ribosomes.

Complete amino acid sequence of chitinase-A from leaves of pokeweed (Phytolacca americana).

The complete amino acid sequence of pokeweed leaf chitinase-A was determined. First all 11 tryptic peptides from the reduced and S-carboxymethylated form of the enzyme were sequenced. Then the same form of the enzyme was cleaved with cyanogen bromide, giving three fragments. The fragments were digested with chymotrypsin or Staphylococcus aureus V8 protease. Last, the 11 tryptic peptides were put in order. Of seven cysteine residues, six were linked by disulfide bonds (between Cys25 and Cys74, Cys89 and Cys98, and Cys195 and Cys208); Cys176 was free. The enzyme consisted of 208 amino acid residues and had a molecular weight of 22,391. It consisted of only one polypeptide chain without a chitin-binding domain. The length of the chain was almost the same as that of the catalytic domains of class IL chitinases. These findings suggested that this enzyme is a new kind of class IIL chitinase, although its sequence resembles that of catalytic domains of class IL chitinases more than that of the class IIL chitinases reported so far. Discussion on the involvement of specific tryptophan residue in the active site of PLC-A is also given based on the sequence similarity with rye seed chitinase-c.

Identification of the aspartic acid residue located at or near substrate-binding site of rye seed chitinase-c.

Carboxyl groups of rye seed chitinase-c (RSC-c) were modified with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and glycine ethyl ester (GEE) at pH 5.5 and 5 degrees C in the presence and absence of (GlcNAc)4. In the absence of (GlcNAc)4, 5.2 carboxyl groups were modified by 90 min-reaction and the chitinase activity was reduced to 2.0%, while in the presence of (GlcNAc)4, 4.6 carboxyl groups were modified and 72% of the activity was retained. To identify the carboxyl group protected by (GlcNAc)4 from the modification, RSC-c was first modified with EDC and GEE in the presence of (GlcNAc)4 and then radiolabeled with EDC and [14C]GEE in the absence of (GlcNAc)4. Analyses of the radioactive peptides from the tryptic and chymotryptic digests of radiolabeled RSC-c showed that the main radiolabeled carboxyl group is that of Asp95, suggesting that Asp95 is located at or near substrate-binding site of RSC-c.

Primary structure of 6.5k-arginine/glutamate-rich polypeptide from the seeds of sponge gourd (Luffa cylindrica).

The amino acid sequence of 6.5k-arginine/glutamate rich polypeptide (6.5k-AGRP) from the seeds of sponge gourd (Luffa cylindrica) has been determined. The 6.5k-AGRP consists of a 47-residue polypeptide chain containing two disulfide bonds, and a molecular mass calculated to be 5695 Da, which fully coincides with a value of [M+H]+ = m/zeta 5693.39 obtained by matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS). The mass spectrometric evidence indicated that 6.5k-AGRP is also present partially truncated at the C-terminus. In our preparations, approximately half of the polypeptide molecules have the C-terminal sequence Arg-Arg-Glu-Val-Asp; the other half lack Val-Asp and end with the glutamic acid, making a total of 45 residues in the polypeptide chain. The two disulfide bonds connect Cys12 to Cys33 and Cys16 to Cys29. Comparison of the amino acid sequence of 6.5k-AGRP with those of the other known proteins included in the PIR protein sequence database showed that it is related to the amino acid sequence of the N-terminal region encoded by the first exon of the cocoa (Theobroma cacao) and cotton seeds vicilin genes, sharing a characteristic two Cys-Xaa-Xaa-Xaa-Cys motif.

Actions of pokeweed antiviral protein on virus-infected protoplasts.

Pokeweed antiviral protein (PAP) belongs to a group of ribosome-inactivating proteins (RIPs) that inactivate ribosomes by depurinating rRNA at a specific site. To study the mechanism for the antiviral activity of PAP, the actions of PAP on TMV-infected and uninfected tobacco protoplasts were investigated. The addition of 0.33 microM PAP to TMV-inoculated protoplasts caused a complete inhibition of TMV production. The same concentration of PAP was found to inhibit protein synthesis in the virus-infected protoplasts and to kill the cells, but it had no effect on the uninfected protoplasts. The concentration dependence of protein synthesis-inhibition by PAP was related to that of inhibition of viral multiplication. Furthermore, two other RIPs (ricin A-chain and luffin-a), which showed 240 and 430-fold less activity on tobacco ribosomes than PAP in a cell-free system, did not inhibit viral multiplication even at a concentration of 3.3 microM. The analysis of RNAs from the virus-infected and PAP-treated protoplasts demonstrated that 25S rRNA was depurinated by PAP in the infected cells. These results suggest that PAP, which is normally unable to penetrate the plasma membrane of uninfected protoplasts, gains entrance to the cytosol of infected cells and prevents viral multiplication by inactivating ribosomes.

The amino acid sequence of mitogenic lectin-B from the roots of pokeweed (Phytolacca americana).

The complete amino acid sequence of pokeweed lectin-B (PL-B) has been analyzed by first sequencing seven lysylendopeptidase peptides derived from the reduced and S-pyridylethylated PL-B and then connecting them by analyzing the arginylendopeptidase peptides from the reduced and S-carboxymethylated PL-B. PL-B consists of 295 amino acid residues and two oligosaccharides linked to Asn96 and Asn139, and has a molecular mass of 34,493 Da. PL-B is composed of seven repetitive chitin-binding domains having 48-79% sequence homology with each other. Twelve amino acid residues including eight cysteine residues in these domains are absolutely conserved in all other chitin-binding domains of plant lectins and class I chitinases. Also, it was strongly suggested that the extremely high hemagglutinating and mitogenic activities of PL-B may be ascribed to its seven-domain structure.

Isolation and molecular characterization of four arginine/glutamate rich polypeptides from the seeds of sponge gourd (Luffa cylindrica).

Four arginine/glutamate rich polypeptides referred to as 5 k-, 6.5 k-, 12.5 k-, and 14 k-AGRPs were purified to homogeneity by gel filtration on Sephadex G-75 followed by CM-cellulose, butyl-Toyopearl 650 M, and reverse-phase HPLC from the seed of sponge gourd (Luffa cylindrica). Tricine SDS-PAGE indicated that 5 k- and 6.5 k-AGRPs are single polypeptides, but 12.5 k- and 14 k-AGRPs consist of two polypeptide chains, which are linked by disulfide bond(s). The N-terminal amino acid sequences of four AGRPs were analyzed by a gas-phase sequencer, and the result indicated that they are distinct molecules. Comparison of the sequences with those of proteins in the protein data base demonstrates that 5 k- and 6.5 k-AGRPs have a significant homology with a basic peptide from pumpkin seeds and with cocoa seed vicilin, respectively, and that 12.5 k- and 14 k-AGRPs are related to 2S seed storage proteins. Furthermore, it was assumed that the four AGRPs might occur in the protein bodies within cells of the seed.

Involvements of Trp23 in the Chitin-binding and of Trp131 in the Chitinase Activity of Rye Seed Chitinase-a.

The oxidation of the tryptophan residues of rye seed chitinase-a (RSC-a) and its isolated catalytic (Cat) domain by N-bromosuccinimide (NBS) was investigated in the absence and presence of oligomers of N-acetylglucosamine (GlcNAc)n. Based on the reactivity toward NBS at pH 5.9, the seven tryptophan residues present in RSC-a are grouped into highly reactive (HR-), low reactive (LR-), and unreactive residues. Analyses of the peptides from 1 tryptophan- and 3 tryptophan-oxidized RSC-a showed that the HR-residue is Trp23 and the LR-residues are Trp131 and Trp141. The chitin-binding ability of RSC-a was lost upon the NBS oxidation of Trp23 at pH 5.9 or pH 7.0. This oxidation was prevented by (GlcNAc)3, which induced a high UV-difference spectrum with maxima at 284 and 293 nm. On the other hand, the chitinase activity of the Cat domain was greatly reduced by the NBS oxidation of Trp131 and Trp141 at pH 5.9, while in the NBS oxidation at pH 6.4, approximately one tryptophan residue was oxidized and about half of the activity was retained. The NBS oxidation of the isolated Cat domain at pH 5.9 was protected by (GlcNAc)4, which induced a UV-difference spectrum with maxima at 284 nm and 293 nm as well as a small trough around 300 nm, similar to that observed in RSC-c. From these results and the previous result that Trp72 in RSC-c is involved in the substrate-binding, it was suggested that Trp23 is highly exposed on the surface of the RSC-a molecule and involved in the chitin-binding, while Trp131 is involved in substrate-binding in its enzyme action.

Crystallization and preliminary X-ray studies of two serine proteinase inhibitors, BGIA and BGIT, from the seeds of bitter gourd.

Two serine proteinase inhibitors from seeds of the bitter gourd, BGIA (bitter gourd inhibitor against acidic amino acid-specific proteinase of Streptomyces griseus) and BGIT (bitter gourd trypsin inhibitor), were crystallized for X-ray structure determination. Crystals of BGIA belong to the monoclinic space group C2 with cell dimensions of a = 54.0 A, b = 23.7 A, c = 47.9 A, and beta = 105.4 degrees, and diffracted X-ray up to 1.5 A resolution. Crystals of BGIT belong to the triclinic space group P1 with cell dimensions of a = 22.8 A, b = 23.5 A, c = 28.4 A, alpha = 93.1 degrees, beta = 99.6 degrees, and gamma = 101.0 degrees, giving X-ray diffraction of over 1.2 A resolution. Intensity data of BGIA and BGIT crystals were collected using synchrotron radiation up to 1.7 and 1.4 A, respectively.

Amino acid sequence and some properties of lectin-D from the roots of pokeweed (Phytolacca americana).

Two pokeweed lectins, designated PL-D1 and PL-D2, have been isolated from the roots of pokeweed (Phytolacca americana) using chitin affinity column chromatography followed by gel filtration on a Sephacryl S-200 column and fast protein liquid chromatography on a Mono-Q column, and their amino acid sequences have been analyzed. PL-D1 consists of 84 amino acid residues and has a molecular mass of 9317, while PL-D2 has an identical sequence with PL-D1 except lack of the C-terminal Leu-Thr. PL-D is composed of two chitin-binding domains, A and B, with 50% homology with each other. Both PL-Ds did not agglutinate native rabbit erythrocytes, but showed about 0.1% of the agglutinating activity of wheat germ agglutinin toward trypsin-treated erythrocytes. In the presence of beta (1-->4) linked oligomers of N-acetyl-D-glucosamine, which inhibit the hemagglutination, PL-D1 had an ultraviolet-difference spectrum with maxima at 292-294 nm and 284-285 nm, attributed to the red shift of the tryptophan residue, suggesting the location of tryptophan residue(s) at or near saccharide-binding site of PL-D1.

Limited proteolysis and reduction-carboxymethylation of rye seed chitinase-a: role of the chitin-binding domain in its chitinase action.

By a limited proteolysis with thermolysin, rye seed chitinase-a (RSC-a) was separated into a N-terminal cysteine-rich chitin-binding (CB-) domain (48 residues) and a catalytic (Cat-) domain (254 residues). The hydrolytic activity of the isolated Cat-domain toward soluble glycolchitin, was similar to that of RSC-a, but that toward insoluble colloidal chitin was 28% of that of RSC-a. Five disulfide bonds in the CB-domain were reduced with 2-mercaptoethanol (2-ME) in the absence of denaturing agents by an "all-or-none" process, that is, once the disulfide bond between Cys15 and Cys42 in the CB-domain was cleaved, the remaining four disulfide bonds were reduced very easily. The reduced and carboxymethylated RSC-a completely lost the chitin-binding ability, but retained 50% of the hydrolytic activity toward colloidal chitin of RSC-a. From these results, it was shown that RSC-a consists of a CB-domain and a Cat-domain connected by a flexible linker, and it was suggested that the CB-domain increases the hydrolytic action of Cat-domain toward insoluble chitin derivatives by binding to them.

Isolation from alpha-zein of thermolysin peptides with angiotensin I-converting enzyme inhibitory activity.

Urea-denatured alpha-zein was almost completely hydrolyzed into small peptides by digestion with 1/100 (w/w) of thermolysin at 37 degrees C for 3h. The angiotensin I-converting enzyme (ACE) inhibitory activity (IC50) of the thermolysin digest of total alpha-zein was 24.5 micrograms/ml, and most of the peptide fractions from Z19 alpha-zein and total alpha-zein separated by reverse-phase HPLC had more or less ACE inhibitory activity. From these fractions, thirty-six peptides, including 5 dipeptides, 14 tripeptides, 9 tetrapeptides, 5 pentapeptides, and 3 hexapeptides, were purified and their amino acid sequences were determined.

Structural analysis of N-linked oligosaccharide of mitogenic lectin-B from the roots of pokeweed (Phytolacca americana).

The structure of an asparagine (N-) linked oligosaccharide of pokeweed lectin-B (PL-B) and the amino acid sequences around two glycosylation sites were identified. The pyridylamino (PA) oligosaccharide prepared from PL-B was eluted as a single peak on both reversed-phase (RP-) HPLC and size-fractionation (SF-) HPLC, and its structure was estimated to be Man alpha 1-->6(Man alpha 1-->3)(Xyl beta 1-->2) Man beta 1-->4GlcNAc beta 1-->4(Fuc alpha 1-->3)GlcNAc by a combination of component analysis, successive exoglycosidase digestions, IS-MS analysis, and 500 MHz 1H-NMR. Two tryptic glycopeptides were isolated from the reduced and S-pyridylethylated PL-B after gel filtration followed by RP-HPLC, indicating the presence of two glycosylation sites in PL-B. The amino acid sequences around the two glycosylation sites were determined to be Cys-Gly-Val-Asp-Phe-Gly-Asn(CHO)-Arg.

Purification and some properties of a beta-xylosidase and an alpha-fucosidase from apple snails (Pomacea canaliculata).

beta-Xylosidase and alpha-fucosidase were purified from the viscera of apple snails (Pomacea canaliculata) using ammonium sulfate precipitation, hydrophobic chromatography on Butyl-Toyopearl, gel filtration on Sephacryl S-300, and Q-Sepharose column chromatography. beta-Xylosidase and alpha-fucosidase are glycoproteins and their molecular masses were estimated to be approximately 85 kDa and 54 kDa by SDS-polyacrylamide gel electrophoresis, and assumed to be about 96 kDa and 230 kDa from their sedimentation coefficients, respectively, indicating that the former is a monomer and the latter has a tetrameric structure. beta-Xylosidase is stable at pH 4-10 and its optimum pH toward pNP-beta-D-xyloside is around 3.6, while alpha-fucosidase is fairly stable at 65 degrees C and pH 4-10, and its optimum pHs toward pNP-alpha-L-fucoside are around 3.2 and 5.2. beta-Xylosidase released a xylose residue from Xylbeta1->2Manbeta1->4GlcNAcbeta1->4(Fucalpha1-> 3)GlcNAc-PA and Manalpha1->6(Manalpha1->3)(Xylbeta1->2)Manbeta1- >4GlcNAcbeta1->4(Fucalpha1->3)GlcNAc-PA, but not from GlcNAcbeta1->2Manalpha1->6(GlcNAcbeta1->2Manalpha1+ ++->3)(Xylbeta1->2)Manbeta1->4GlcNAcbeta1-> 4(Fucalpha1->3)GlcNAc-PA, while alpha-fucosidase released a fucose residue from these three PA-oligosaccharides.

The complete amino acid sequence of lectin-C from the roots of pokeweed (Phytolacca americana).

The complete amino acid sequence of pokeweed lectin-C (PL-C) consisting of 126 residues has been determined. PL-C is an acidic simple protein with molecular mass of 13,747 Da and consists of three cysteine-rich domains with 51-63% homology. PL-C shows homology to chitin-binding proteins such as wheat germ agglutinin, and all eight cysteine residues in the three domains of PL-C are completely conserved in all other chitin-binding domains.

The complete amino acid sequence of chitinase-B from the leaves of pokeweed (Phytolacca americana).

The complete amino acid sequence of pokeweed leaf chitinase-B (PLC-B) has been determined by first sequencing all 19 tryptic peptides derived from the reduced and S-carboxymethylated (RCm-) PLC-B and then connecting them by analyzing the chymotryptic peptides from three fragments produced by cyanogen bromide cleavage of RCm-PLC-B. PLC-B consists of 274 amino acid residues and has a molecular mass of 29,473 Da. Six cysteine residues are linked by disulfide bonds between Cys20 and Cys67, Cys50 and Cys57, and Cys159 and Cys188. From 58-68% sequence homology of PLC-B with five class III chitinases, it was concluded that PLC-B is a basic class III chitinase.