Surprisingly high stability of barley lipid transfer protein, LTP1, towards denaturant, heat and proteases

Tripeptidyl peptidase-I (TPP-I) is a lysosomal peptidase which cleaves tripeptides from the N-terminus of peptides. The function of the enzyme is unclear but its importance is demonstrated by the fact that mutations in TPP-I are responsible for late infantile neuronal ceroid lipofuscinosis, a lethal lysosomal storage disease. As a step towards identifying its natural substrates, we have used a series of synthetic peptides, based on angiotensin-II, to explore the effects of peptide chain length and the effects of amino acid substitutions at the P₁ and P₁′ positions on the rate of catalysis. With the exception of angiotensin-(1–8) (angiotensin-II), which is a relatively poor substrate for TPP-I, the rate of catalysis increases with increasing chain length. K_cat/K_m values increase 50-fold between angiotensin-(1–5) and angiotensin-(1–14). TPP-I shows little specificity for the nature of the amino acids in the P₁ and P₁′ positions, K_cat/K_m values varying only 5-fold for a range of substitutions. However, Pro or Lys in the P₁ position and Pro in the P₁′ positions are incompatible with TPP-I activity. These observations suggest that TPP-I is a non-specific, but essential, peptidase involved in the latter stages of lysosomal protein degradation.     

Purification and characterization of two serine carboxypeptidases from Aspergillus niger and their use in C-terminal sequencing of proteins and peptide synthesis.

A procedure was developed to prepare in large amounts two carboxypeptidases, CPD-I and CPD-II, from Aspergillus niger. They were each shown to be serine proteases and single-chain monomers with molecular masses of ca. 81 kDa and containing 22% carbohydrates. Amino acid analysis, carbohydrate determination, and N-terminal sequencing (20 to 25 residues) were performed on each enzyme. CPD-I showed sequence homologies with malt carboxypeptidase II, while the N terminus of CPD-II was different from that of any known serine carboxypeptidase. Like carboxypeptidase Y from Saccharomyces cerevisiae and carboxypeptidase III from malt, CPD-II contained a free sulfhydryl group that could play a role in catalysis. Both A. niger enzymes had pH optima of about 4 and were unstable above pH 7. Their specificities for substrate positions P1 and P'1 were characterized by use of, as substrates, a series of N-blocked amino acid esters and dipeptides. Both enzymes were specific for Arg, Lys, and Phe in P1. CPD-I preferred hydrophobic residues in P'1, while CPD-II was highly specific for Arg and Lys in this position. Each displayed an original specificity when P1 and P'1 were considered together. The specificities were also studied by analyzing the time course of the release of amino acids from eight different peptides of various lengths. CPD-I and CPD-II appeared to be quite suitable for C-terminal sequence studies as well as for the synthesis of peptide bonds. The latter was studied with two peptide esters as aminolysis substrates and a series of amino acid amides as nucleophiles.(ABSTRACT TRUNCATED AT 250 WORDS)     

Purification and characterization of two serine carboxypeptidases from Aspergillus niger and their use in C-terminal sequencing of proteins and peptide synthesis.

A procedure was developed to prepare in large amounts two carboxypeptidases, CPD-I and CPD-II, from Aspergillus niger. They were each shown to be serine proteases and single-chain monomers with molecular masses of ca. 81 kDa and containing 22% carbohydrates. Amino acid analysis, carbohydrate determination, and N-terminal sequencing (20 to 25 residues) were performed on each enzyme. CPD-I showed sequence homologies with malt carboxypeptidase II, while the N terminus of CPD-II was different from that of any known serine carboxypeptidase. Like carboxypeptidase Y from Saccharomyces cerevisiae and carboxypeptidase III from malt, CPD-II contained a free sulfhydryl group that could play a role in catalysis. Both A. niger enzymes had pH optima of about 4 and were unstable above pH 7. Their specificities for substrate positions P1 and P'1 were characterized by use of, as substrates, a series of N-blocked amino acid esters and dipeptides. Both enzymes were specific for Arg, Lys, and Phe in P1. CPD-I preferred hydrophobic residues in P'1, while CPD-II was highly specific for Arg and Lys in this position. Each displayed an original specificity when P1 and P'1 were considered together. The specificities were also studied by analyzing the time course of the release of amino acids from eight different peptides of various lengths. CPD-I and CPD-II appeared to be quite suitable for C-terminal sequence studies as well as for the synthesis of peptide bonds. The latter was studied with two peptide esters as aminolysis substrates and a series of amino acid amides as nucleophiles.(ABSTRACT TRUNCATED AT 250 WORDS)     

SDS-subtilisin catalyzed synthesis of tetra-peptides containing multifunctional amino acid residues in ethanol

The role of acyl donor structure on the course of peptide bond formation catalyzed by SDS-subtilisin in ethanol was investigated. In the reaction Z---Ala---Ala---Leu---OR+H---Phe---pNA→Z---Ala---Ala---Leu---Phe---pNA, nearly quantitative product yields were observed after 2 h, regardless of whether an activated (R=CH₃, p-C₆H₅Cl) or non-activated (R=H) acyl donor was used. It was found that the enzyme can accept as acyl donors N-protected tri-peptides containing basic or acidic amino acid residues in the P₁-position. Tetra-peptides of general formula Z---Ala---Ala---P₁---P₁′---pNA, where P₁=Glu, Asp, Lys, Arg or His and P₁′=Phe, Arg or Glu have been obtained in good yield.     

C-terminal amidation of acylamino acids and peptides using a transpeptidation method catalyzed by carboxypeptidase Y

The carboxypeptidase Y-catalyzed reaction of acyl transfer of acylamino acid and peptide residues from the corresponding esters to ammonia and to amides of amino acids has been studied, and conditions for obtaining amides of amino acids and peptides with the yields up to 90% found.     

A two-step enzymatic synthesis of dipeptides

A simple system is introduced to produce dipeptides continuously by enzyme catalyzed condensation of amino acid esters and amino acid amides. Synthesis of N-terminal free dipeptide-amides is achieved by means of carboxypeptidase Y. The peptide-amide is deamidated utilizing a newly isolated peptide-amide is deamidated utilizing a newly isolated peptide-amidase. Separation of substrates and products is accomplished by anion-exchange chromatography. Modeling of the reactions shows that the two reactions have to be carried out in a cascade of two reactors in order to prevent hydrolysis of the peptide by the carboxypeptidase. Continuous production of Kyotorphin (H-TyrArg-OH) with a space-time yield of 257 g/L . d shows the feasibility of this concept.     

Prosomatostatin is proteolytically processed at the amino terminal segment by subtilase SKI-1

Processing of prohormones to generate active products typically occurs at basic residues via cleavage by proprotein convertases. A less common type of cleavage is mediated at hydrophobic (L, V, F, N) or small amino acid (A, T, S) residues. Efforts to identify the proteinases responsible for processing precursors at their hydrophobic amino acids has led to the recent cloning of a new type-1 membrane-bound subtilase called SKI-1. The NH₂-terminal region of prosomatostatin, previously shown to contain a sorting signal for the regulated secretory pathways, is processed to generate PSST_[1–10]. The exact cleavage mechanism is unknown, but has been assumed to involve monobasic processing at Lys¹³ followed by carboxypeptidase trimming. We found that K13A mutation did not block PSST_[1–10] production. Since the prosomatostatin sequence R⁸–Q⁹–F¹⁰–L¹¹↓ qualifies as a potential SKI-1 substrate, using a vaccinia virus expression system along with HPLC and radioimmunoassays, we observed that overexpression of recombinant SKI-1 in COS-1 and HEK-293 cells significantly increased the production of PSST_[1–10]. Additionally, in CHO cells lacking SKI-1, there was a significant reduction in PSST_[1–10] production which could be increased upon SKI-1 stimulation. Mutagenesis studies showed that efficient processing of PSST to PSST_[1–10] required the RXRXXL motif. However, this NH₂-terminal cleavage was not a prerequisite for the formation of SST-14 and SST-28.     

Estradiol and progesterone synthesis in human placenta is stimulated by calcitriol

Calcitriol exerts a diverse range of biological actions including the control of growth and cell differentiation, modulation of hormone secretion, and regulation of reproductive function. The placenta synthesizes calcitriol through the expression of CYP27B1, but little is known about local actions of this hormone in the fetoplacental unit. The objective of this study was to investigate the effects of calcitriol upon progesterone (P₄) and estradiol (E₂) secretion in trophoblasts cultured from term human placenta. Cells were incubated in the presence of calcitriol for 18 h and pregnenolone or androstenedione were subsequently added as substrates for the 3β-hydroxysteroid dehydrogenase (3β-HSD) or P450-aromatase (CYP19), respectively. Calcitriol stimulated in a dose-dependant manner E₂ and P₄ secretion. The use of a selective inhibitor of PKA prevented the effects of calcitriol upon E₂ secretion, but not on P₄. These results show that calcitriol is a physiological regulator of placental E₂ and P₄ production and suggest a novel role for calcitriol upon placental steroidogenesis.     

Use of a 49-peptide library for a qualitative and quantitative determination of pseudomonal serralysin specificity

The Pseudomonas aeruginosa serralysin (E.C. 3.4.24.40.), which is a zinc-dependent metalloprotease from the metzincin superfamily, has quite a broad specificity, which has not yet been clearly identified. We have studied it with an original approach, using a 49-peptide library of the type Z–AXXA (amide) (X=A, L, V, F, S, R, E). The library was analyzed by LC-MS before and after enzymatic hydrolysis. A great number of hydrolyzed peptides were screened and the preferential hydrolysis was the X–X peptide bond, even if in some cases, A–X and X–A bond could be hydrolyzed. No amino acids with a ionized side chain could be found in the P₁′ position. The results obtained suggest that the specificity in the P_n′ position, where an hydrophobic residue was preferentially found, seems more selective that in the P_n position. The P₁ position was not very specific, but, on a quantitative point of view, the enzymatic activity was particularly increased when R, F or A were in this position. The results allow us to define the P₁′ and P₁ residues for an optimal substrate of pseudomonal serralysin and usable for the design and the synthesis of a specific inhibitor.     

Substrate specificities of cathepsin A,L and A,S from pig kidney

The substrate specificities of two different molecular sizes of cathepsin A, A,L (large form) and A,S (small form), for synthetic substrates were examined kinetically. Both enzymes showed a similar broad substrate specificity against various acyl dipeptides, amino acid esters, and amino acid amides. Z-Phe-Ala and Ac-Phe-OEt were good substrates. Peptides containing hydrophobic amino acids were hydrolyzed rapidly. The presence of hydrophobic amino acid residues, not only at the C-terminal position but also at the second position and probably the third position from the C-terminal, resulted in an increase in the rate of hydrolysis. Peptides containing glycine and proline were hydrolyzed slowly. Inhibition studies with Z-D-Phe-D-Ala and Z-Phe suggested that the peptidase and esterase activities of the enzymes are both catalyzed by the same site of the enzyme molecule, but it remains to be elucidated whether or not the binding sites for peptides and esters are the same.     

alpha-Chymotrypsin as the catalyst for peptide synthesis.

alpha-Chymotrypsin (EC 3.4.21.1)-catalysed syntheses of peptides were performed with various N-acylated amino acid or peptide esters as donors, and amino acid derivatives, peptides or their derivatives as acceptors. Under optimal conditions the synthesis was almost quantitative. As acceptor nucleophiles, free amino acids or the ester derivatives were inadequate, but amino acid amides or hydrazides, di- or tri-peptides, or the amides, hydrazides and esters of the peptides were useful. The nucleophile specificity for synthesis was markedly similar to the leaving-group specificity in hydrolysis; hydrophobic or bulky amino acid residues were most effecient at both P1' and P2' positions [notation of Schechter & Berger (1967) Biochem. Biophys. Res. Commun. 27, 157-162], but L-proline as well as D-amino acid residues were the worst choices. The synthesis was further dependent on the solubility of the products synthesized; a higher yield of products was expected with lower solubility. As donor esters, good substrates were all useful. Accordingly, fragment condensation was possible by using N-acylated peptide esters and various peptides. The present study suggested that alpha-chymotrypsin may become a useful tool for peptide synthesis.     

Isolation, molecular cloning, and partial characterization of a novel carboxypeptidase B from human plasma

A novel plasminogen-binding protein has been isolated from human plasma utilizing plasminogen-Sepharose affinity chromatography. This protein copurified with alpha 2 antiplasmin when the plasminogen affinity column was eluted with high concentrations of epsilon-aminocaproic acid (greater than 20 mM). Analysis by sodium dodecyl sulfate suggests this protein has an apparent Mr of 60,000. The amino-terminal amino acid sequence showed no similarity to other protein sequences. Based on the amino-terminal amino acid sequence, oligonucleotide probes were designed for polymerase chain reaction primers, and an approximately 1,800 base pair cDNA was isolated that encodes this Mr 60,000 protein. The deduced amino acid sequence reveals a primary translation product of 423 amino acids that is very similar to carboxypeptidase A and B and consists of a 22-amino acid signal peptide, a 92-amino acid activation peptide, and a 309-amino acid catalytic domain. This protein shows 44 and 40% similarity to rat procarboxypeptidase B and human mast cell procarboxypeptidase A, respectively. The residues critical for catalysis and zinc and substrate binding of carboxypeptidase A and B are conserved in the Mr 60,000 plasminogen-binding protein. The presence of aspartic acid at position 257 of the catalytic domain suggests that this protein is a basic carboxypeptidase. When activated by trypsin, it hydrolyzes carboxypeptidase B substrates, hippuryl-Arg and hippuryl-Lys, but not carboxypeptidase A substrates, and it is inhibited by the specific carboxypeptidase B inhibitor (DL-5-guanidinoethyl)mercaptosuccinic acid. We propose that the Mr 60,000 plasminogen-binding protein isolated here is a novel human plasma carboxypeptidase B and that it be designated pCPB.     

A novel metalloprotease from Bacillus cereus for protein fibre processing

A novel protease produced by Bacillus cereus grown on wool as carbon and nitrogen source was purified. B. cereus protease is a neutral metalloprotease with a molecular mass of 45.6 kDa. The optimum activity was at 45 °C and pH 7.0. The substrate specificity was assessed using oxidized insulin B-chain and synthetic peptide substrates. The cleavage of the insulin B-chain was determined to be Asn³, Leu⁶, His¹⁰-Leu¹¹, Ala¹⁴, Glu²¹, after 12 h incubation. Among the peptide substrates, the enzyme did not exhibit activity towards ester substrates; with p-nitroanilide, the kinetic data indicate that aliphatic and aromatic amino acids were the preferred residues at the P₁ position. For furylacryloyl peptides substrates, which are typical substrates for thermolysin, the enzyme exhibited high hydrolytic activity with a K_m values of 0.858 and 2.363 mM for N-(3-[2-Furyl]acryloyl)-Ala-Phe amide and N-(3-[2-Furyl]acryloyl)-Gly-Leu amide, respectively. The purified protease hydrolysed proteins substrates such as azocasein, azocoll, keratin azure and wool.     

The specificity of carboxypeptidase Y may be altered by changing the hydrophobicity of the S'1 binding pocket.

The S'1 binding pocket of carboxypeptidase Y is hydrophobic, spacious, and open to solvent, and the enzyme exhibits a preference for hydrophobic P'1 amino acid residues. Leu272 and Ser297, situated at the rim of the pocket, and Leu267, slightly further away, have been substituted by site-directed mutagenesis. The mutant enzymes have been characterized kinetically with respect to their P'1 substrate preferences using the substrate series FA-Ala-Xaa-OH (Xaa = Leu, Glu, Lys, or Arg) and FA-Phe-Xaa-OH (Xaa = Ala, Val, or Leu). The results reveal that hydrophobic P'1 residues bind in the vicinity of residue 272 while positively charged P'1 residues interact with Ser297. Introduction of Asp or Glu at position 267 greatly reduced the activity toward hydrophobic P'1 residues (Leu) and increased the activity two- to three-fold for the hydrolysis of substrates with Lys or Arg in P'1. Negatively charged substituents at position 272 reduced the activity toward hydrophobic P'1 residues even more, but without increasing the activity toward positively charged P'1 residues. The mutant enzyme L267D + L272D was found to have a preference for substrates with C-terminal basic amino acid residues. The opposite situation, where the positively charged Lys or Arg were introduced at one of the positions 267, 272, or 297, did not increase the rather low activity toward substrates with Glu in the P'1 position but greatly reduced the activity toward substrates with C-terminal Lys or Arg due to electrostatic repulsion. The characterized mutant enzymes exhibit various specificities, which may be useful in C-terminal amino acid sequence determinations.     

Selective activation of G alpha i mediated signalling of S1P3 by FTY720-phosphate

The immune modulator FTY720 is phosphorylated in vivo to FTY720 phosphate (FTY-P), which activates four sphingosine 1-phosphate (S1P) receptors including S1P₃. Upon activation with S1P, S1P₃ couples to G_i- and G_q-protein-dependent signalling pathways. Here we show that FTY-P selectively activates the S1P₃-mediated and G_i-coupled inhibition of adenylyl cyclase. Contemporaneously, it antagonizes the S1P-induced activation of G_q via S1P₃ in intracellular calcium flux measurements, GTP-binding experiments, and flow cytometric analyses of activation-induced receptor down-regulation. In contrast to S1P, pre-treatment with FTY-P did not desensitize S1P-induced calcium flux or chemotaxis via S1P₃. The lack of receptor desensitization prevented S1P₃-mediated migration to FTY-P. Human umbilical vein endothelial cells express S1P₁ and S1P₃, and respond to S1P and FTY-P by ERK1/2 phosphorylation and by intracellular calcium release in a pertussis toxin-sensitive manner. But whereas a mixture of S1P and FTY-P was not affecting ERK1/2 phosphorylation, the intracellular calcium flux was hampered with increasing amounts of FTY-P, which points to a cross-talk between S1P₁ and S1P₃. FTY-P is therefore one of the rare ligands which bind to a receptor that couples multiple G-proteins but selectively activates only one signalling pathway.     

Uptake and light activated esterification of P by isolated chloroplasts

1. 1. Esterification of ³²P₁ by illuminated chloroplasts prepared on a sucrose gradient was examined to establish the optimal incubation conditions.

2. 2. The evidence is consistent with phosphorylation being closely coupled to the sum of noncyclic and pseudocyclic electron flow and with the rate of electron flow responding to the availability of electron acceptors.

3. 3. Apparent K_m values for ADP and Mg²⁺ were found to be 40 and 250 μM, respectively. The K_m value for Mg²⁺ was increased by the presence of Ca²⁺. Two apparent values were observed for P₁ at 0.2 and 1.1 mM. Chloroplast damage resulted in increased apparent K_m (P₁) values.

4. 4. Acceleration of the esterification resulting from the addition of ADP and P₁ to the medium indicated that these compounds were able to penetrate to the active site of esterification.

5. 5. Ribose 5-phosphate (Rib-5-P) was shown to inhibit P₁ esterification without affecting the apparent K_m for ADP or P₁. The evidence suggests that Rib-5-P interferes with the uptake of P₁, and possibly ADP.

栽培介质、营养液及化学药剂对红掌生长开花的影响

采用泥炭:珍珠岩:沙(1:1:1)、珍珠岩和水3种栽培介质及3个配方的营养液对红掌进行无土栽培,结果表明,以水作为介质,营养液配方为N:P₂O₅:K₂O=4:1:8的培养液对红掌株高、叶片数及植株净重的增加效果最好,但水培对红掌开花无促进作用。以水为介质的红掌经高温(32℃)胁迫后叶片黄化数为零,显著低于其它处理组;而在泥炭:珍珠岩:沙(1:1:1)介质中,则是6-BA处理的叶片黄化数明显低于其它处理组。     

Multiple proteolytic action of rat liver cathepsin B: specificities and pH-dependences of the endo- and exopeptidase activities.

Dipeptidylcarboxypeptidase, endopeptidase, and carboxypeptidase activities of rat liver cathepsin B were investigated using soluble denatured protein substrates, reduced and S-(3-trimethylammonio)propylated proteins and their derivatives. It was found that the soluble denatured proteins were degraded mainly by the dipeptidylcarboxypeptidase activity and in a few cases by the endopeptidase and carboxypeptidase activities. The eipeptidylcarboxypeptidase activity showed broad substrate specificity with broad pH optimum at 4-6. A peptide having the alpha-carboxyl group amidated with methylamine could also be a good substrate for this activity. These results suggest that this activity is dependent not upon the dissociated alpha-carboxyl group at the P2' site but upon the hydrogen-bonding abilities of the alpha-imino moiety and the protonated or amidated alpha-carboxyl moiety at P2'. On the other hand, the endopeptidase and carboxypeptidase activities were observed in a few cases, suggesting that special amino acid sequences in the substrates are responsible for these activities. These activities showed sharp pH optima at 6 and seemed to prefer basic amino acid residues at P1 site. Therefore, we suppose that cathepsin B has a carboxyl group with a pKa of about 5.5 at the S1 subsite which more effectively interacts with a positive charge at the P1 site of the substrate at pH 6 than at pH 5. Based on these results, a model of the binding subsites of this enzyme is proposed.     

Effects of Inorganic Oxides, Sulfides, Chlorides, and Acid Chlorides on Metachromasia and Other Staining Properties

The ability of 17 inorganic compounds (POCl₃, PSC1₃, PC1₃, P₂O₅, P₂S₅, P₄S₃, P₄S₇, PC1₅, Sb₂O₅, As₂O₅, BiOC1₂, SeOC1₂, SO₂C1₂, Sb₂S₅, VOC1₂, SiC1₄ and CrO₂Cl₂) dissolved in pyridine or 2,2,4-trimethyl pentane, to enhance subsequent staining of tissue components with toluidine blue, phosphotungstic acid-hematoxylin (PTAH), leukofuchsin, and dihydroxydinaphthyl-disulfide (DDD) was studied. Eight of these compounds were also tested for ability to enhance staining with Alcian blue 8GN and Luxol fast blue MBS. Nine of the 17 compounds produced increased staining of certain tissue components with leukofuchsin, 13 with toluidine blue, 16 with PTAH, and 16 with DDD. The results suggest additional approaches to identification of tissue entities by induced metachromatic basophilia and leukofuchsin positivity as well as by the other stains studied, and also suggest a number of hitherto unstudied modes of reaction between the dyes used and reactive groups of tissue components. Many reactions of the compounds tested, with reactive groups known to be present in tissue components, are basecatalyzed, so that choice of solvent can influence the results obtained.     

KMI-008, a novel beta-secretase inhibitor containing a hydroxymethylcarbonyl isostere as a transition-state mimic: design and synthesis of substrate-based octapeptides

A novel class of substrate-based β-secretase (BACE1) inhibitors containing a hydroxymethylcarbonyl (HMC) isostere was designed and synthesized. Phenylnorstatine [(2R,3S)-3-amino-2-hydroxy-4-phenylbutyric acid; Pns] was an effective transition-state mimic at the P₁ position. Structure–activity relationships (SARs) of the P₃–P₃′ positions of BACE1 inhibitors were studied.