Disulfide arrangement of human insulin-like growth factor I derived from yeast and plasma.

The disulfide arrangement of yeast derived human insulin-like growth factor I (yIGF-I) was determined using a combination of Staphylococcus aureus V8 protease mapping, fast-atom-bombardment mass spectrometry as well as amino acid sequence and composition analysis. Three disulfide bridges were found between the following cysteine residues: Cys6-Cys48, Cys47-Cys52 and Cys18-Cys61. IGF-I isolated from human plasma (pIGF-I) was found to have an identical disulfide configuration. A yeast-derived isomeric form of IGF-I (yisoIGF-I) exhibited an altered disulfide arrangement: Cys6-Cys47, Cys48-Cys52 and Cys18-Cys61. Radioreceptor analysis of pIGF-I and yIGF-I showed high specific activity, 20,000 U/mg. However, yisoIGF-I demonstrated a severely reduced ability to bind to the IGF-I receptor (19%) and was less potent in provoking a mitogenic response in Balb/C 3T3 fibroblasts (50% at doses 10-100 ng/ml). The data demonstrate the importance of correct disulfide arrangement in IGF-I for full biological activity.     

The synthesis and biologic evaluation of anti-platelet and cytotoxic β-nitrostyrenes

Our previous studies demonstrated that two cytotoxic β-nitrostyrene derivatives, 3,4-methylenedioxy-β-nitrostyrene (MNS) and 4-O-benzoyl-3-methoxy-β-nitrostyrene (BMNS) exhibit potent anti-platelet activities. In this study, a series of β-nitrostyrenes were synthesized and subjected to anti-platelet aggregation assay and cytotoxicity assay. The mono- and di-substitutions on the B ring of BMNS tended to increase the anti-platelet activity and decrease the cytotoxic activity. Of these, compounds 19 and 24 exhibited the most potent inhibitory effects on thrombin- and collagen-induced platelet aggregation (IC₅₀ ? 0.7 μM) without significant cytotoxicity on a human cancer cell line (up to 20 μM). Further studies indicated that compounds 19 and 24 inhibited platelet aggregation via prevention of glycoprotein IIb/IIIa activation. The potent and novel effects of BMNS derivatives make them attractive candidates for the development of new anti-platelet agents.     

Roles of Gln81 and Cys80 in catalysis by glycosylphosphatidylinositol-phospholipase C from Trypanosoma brucei.

Glycosylphosphatidylinositol-specific phospholipase C (GPtdIns-PLC) is found in the protozoan parasite Trypanosoma brucei. A region of protein sequence similarity exists between the protozoan enzyme and eubacterial phosphatidylinositol-phospholipases C. The functional relevance of Cys80 and Gln81 of GPtdIns-PLC, both in this region, was tested with a panel of mutations at each position. Gln81Glu, Gln81Ala, Gln81Gly, Gln81Lys and Gln81Leu mutants were inactive. Cleavage of GPtdIns was detectable in Gln81Asn, although the specific activity decreased 500-fold, and kcat was reduced 50-fold. Thus an amide side-chain at residue 81 is essential for catalysis by GPtdIns-PLC. Sulfhydryl reagents inactivate GPtdIns-PLC, suggesting that a Cys could be close to the enzyme active site. Surprisingly, p-chloromercuriphenyl sulfonate (p-CMPS) is significantly more potent than N-ethylmaleimide, the less bulky compound. This knowledge prompted us to test whether replacement of Cys80 with an amino acid possessing a bulky side-chain would inactivate GPtdIns-PLC: Cys80Ala, Cys80Thr, Cys80Phe, Cys184Ala, and Cys269-270-273Ser were constructed for that purpose. Cys80Phe lacked enzyme activity, while Cys80Ala, Cys80Thr and Cys269-270-273Ser retained 33 to 100% of wild-type activity. Interestingly, the Cys80Ala and Cys80Thr mutants became resistant to p-CMPS, as predicted if the sulfhydryl reagent reacted with Cys80 in the wild-type enzyme to form a cysteinyl mercurylphenylsulfonate moiety, a bulky adduct that inactivated GPtdIns-PLC, similar to the Cys80Phe mutation. We conclude that a bulky side-chain (or adduct) at position 80 of GPtdIns-PLC abolishes enzyme activity. Together, these observations place Cys80 and Gln81 at, or close to, the active site of GPtdIns-PLC from T. brucei.     

Evaluation of caffeic acid amide analogues as anti-platelet aggregation and anti-oxidative agents

A series of amides of caffeic acid were synthesized and evaluated for their anti-platelet and anti-oxidative activities. N-(2-Bromo-phenyl)-3-(3,4-dihydroxy-phenyl)-acrylamide (12) and N-(3-Bromo-phenyl)-3-(3,4-dihydroxy-phenyl)-acrylamide (13) exhibited potent inhibitory activity (IC(50)=5.8 and 6.7 microM, respectively) against arachidonic acid-induced (AA) platelet aggregation, comparable with invalid caffeic acid. Most of the synthesized caffeic acid anilides exhibited the promising anti-platelet aggregation in AA-induced assay and anti-oxidative activities. This study also exhibited that caffeic anilides displayed more potent anti-oxidative activity in the radical scavenging activity assay than trolox and vitamin E.     

重组双功能水蛭素的发酵、纯化和鉴定

构建了重组双功能水蛭素 ( Recombinant-RGD-Hirudin、 r-RGD-Hirudin ) cDNA 的表达质粒 RGD-Hirudin-pPIC9K,转化入毕赤酵母中,经筛选得到高表达的阳性克隆。种子菌经过3d发酵培养,其培养液上清经超滤浓缩、凝胶过滤层析和离子交换层析后,得到纯度大于97%、比活性为 12000 ATU/mg 的 r-RGD-Hirudin,回收率大于60%,发酵产率为 1 g/L。纯化后的 r-RGD-Hirudin 经过还原SDS-PAGE,抗凝血酶活力分析、抗血小板聚集分析、质谱分析及等电聚焦分析等方法鉴定,证明该表达产物为水蛭素的衍生物,具有抗凝血酶和抗血小板聚集双重功能。     

Site-specific labeling of cytoplasmic peptide:N-glycanase by N,N'-diacetylchitobiose-related compounds

Peptide:N-glycanase (PNGase) is the deglycosylating enzyme, which releases N-linked glycan chains from N-linked glycopeptides and glycoproteins. Recent studies have revealed that the cytoplasmic PNGase is involved in the degradation of misfolded/unassembled glycoproteins. This enzyme has a Cys, His, and Asp catalytic triad, which is required for its enzymatic activity and can be inhibited by "free" N-linked glycans. These observations prompted us to investigate the possible use of haloacetamidyl derivatives of N-glycans as potent inhibitors and labeling reagents of this enzyme. Using a cytoplasmic PNGase from budding yeast (Png1), Man9GlcNAc2-iodoacetoamide was shown to be a strong inhibitor of this enzyme. The inhibition was found to be through covalent binding of the carbohydrate to a single Cys residue on Png1, and the binding was highly selective. The mutant enzyme in which Cys191 of the catalytic triad was changed to Ala did not bind to the carbohydrate probe, suggesting that the catalytic Cys is the binding site for this compound. Precise determination of the carbohydrate attachment site by mass spectrometry clearly identified Cys191 as the site of covalent attachment. Molecular modeling of N,N'-diacetylchitobiose (chitobiose) binding to the protein suggests that the carbohydrate binding site is distinct from but adjacent to that of Z-VAD-fmk, a peptide-based inhibitor of this enzyme. These results suggest that cytoplasmic PNGase has a separate binding site for chitobiose and other carbohydrates, and haloacetamide derivatives can irreversibly inhibit that catalytic Cys in a highly specific manner.     

Evidence that the methylesterase of bacterial chemotaxis may be a serine hydrolase.

CheB, the methylesterase of chemotactic bacteria, catalyzes the hydrolysis of glutamyl-methyl esters in bacterial chemoreceptor proteins. The two cysteines predicted by the amino acid sequence of CheB were replaced by alanine residues. The resulting mutants, Cys207-Ala, Cys309-Ala and a double cysteine mutant Cys207-Ala/Cys309-Ala, retained methylesterase activity, indicating that sulfhydryls are not crucial for CheB mediated catalysis. A homology search revealed a conserved serine active-site region between residues 162 and 166 which is homologous to the active-site region of acetylcholine esterases, suggesting that Ser164 of CheB is the active-site nucleophile. Oligonucleotide-directed mutagenesis was used to change the serine to a cysteine. This Ser164-Cys mutant had less than 2% of the wild-type activity. Unlike the serine proteinases which utilize a 'catalytic triad' mechanism, CheB does not have the conserved histidine and aspartic acid residues located in positions N-terminal to the active-site serine. In addition, CheB is not labeled with di-isopropylfluorophosphate, a potent inhibitor of other serine hydrolases. A novel mechanism is proposed for CheB involving substrate-assisted catalysis to account for these apparent anomalies.     

Synthesis and evaluation of nitric oxide-releasing derivatives of 3-n-butylphthalide as anti-platelet agents

Most ischemic stroke results from brain blood vessel blockage by platelet-mediated thrombus, and anti-platelet therapy has been demonstrated clinical benefits in the treatment of this disease. In the present work, novel nitric oxide (NO)-releasing derivatives of an anti-ischemic stroke drug 3-n-butylphthalide (NBP) were synthesized. Compounds 7a and 7c exhibited more potent anti-platelet activity than NBP and aspirin, and released a moderate amount of NO, which is beneficial in improving cardiovascular and cerebral circulation. These findings provide an alternative approach to the development of drugs more potent than NBP for the intervention of ischemic stroke.     

Receptor binding activity and cytosolic free calcium response by synthetic endothelin analogs in cultured rat vascular smooth muscle cells

Using a variety of synthetic analogs of porcine endothelin (pET), we have studied the effects of these analogs on receptor binding activity and cytosolic free Ca2+ concentrations ([Ca2+]i) in cultured rat vascular smooth muscle cells (VSMC). Removal of C-terminal Trp21 residue, truncated derivatives pET(1-15) and (16-21), substitution of disulfide bond, Cys(3-11) or Cys(1-15), by Cys (Acm), all resulted in a complete loss of receptor binding activity and [Ca2+]i response, while N-terminal elongation of Lys-Arg residues, but not oxidation of Met7 residue, decreased receptor binding activity and [Ca2+]i response. [Cys1-15,Cys3-11]pET was far more potent than [Cys1-11,Cys3-15]pET in receptor binding and [Ca2+]i response. These data indicate that the C-terminal Trp21 as well as the proper double cyclic structure formed by the intramolecular disulfide bonds of the pET molecule are essential for receptor binding and subsequent [Ca2+]i increase in rat VSMC.     

Interaction of synthetic sarafotoxin with rat vascular endothelin receptors

The effects of synthetic analogs of sarafotoxin (STX) S6b, a snake venom peptide with a high sequence homology to the endothelium-derived vasoconstrictor endothelin (ET), on ET receptor binding activity and cytosolic free Ca2+ concentration [( Ca2+]i) were studied in cultured rat vascular smooth muscle cells. Binding studies revealed that [Cys1-15, Cys3-11] STX competed with 125I-ET for the binding to its vascular receptors with lower affinity than that of ET, but was far more effective than [Cys1-11, Cys3-15]STX in inhibiting the binding. [Cys1-15, Cys3-11]STX had a less potent effect on increasing [Ca2+]i than ET, whereas [Cys1-11, Cys3-15]STX was inactive. These data suggest that there may exist heterogenous subpopulations of the vascular ET/STX receptors, and that the proper double cyclic structure of STX is essential for interacting with its putative receptors to induce the [Ca2+]i response.     

High efficacy and minimal peptide required for the anti‐angiogenic and anti‐hepatocarcinoma activities of plasminogen K5

Kringle 5(K5) is the fifth kringle domain of human plasminogen and its anti‐angiogenic activity is more potent than angiostatin that includes the first four kringle fragment of plasminogen. Our recent study demonstrated that K5 suppressed hepatocarcinoma growth by anti‐angiogenesis. To find high efficacy and minimal peptide sequence required for the anti‐angiogenic and anti‐tumour activities of K5, two deletion mutants of K5 were generated. The amino acid residues outside kringle domain of intact K5 (Pro452‐Ala542) were deleted to form K5mut1(Cys462‐Cys541). The residue Cys462 was deleted again to form K5mut2(Met463‐Cys541). K5mut1 specifically inhibited proliferation, migration and induced apoptosis of endothelial cells, with an apparent two‐fold enhanced activity than K5. Intraperitoneal injection of K5mut1 resulted in more potent tumour growth inhibition and microvessel density reduction than K5 both in HepA‐grafted and Bel7402‐xenografted hepatocarcinoma mouse models. These results suggested that K5mut1 has more potent anti‐angiogenic activity than intact K5. K5mut2, which lacks only the amino terminal cysteine of K5mut1, completely lost the activity, suggesting that the kringle domain is essential for the activity of K5. The activity was enhanced to K5mut1 level when five acidic amino acids of K5 in NH₂ terminal outside kringle domain were replaced by five serine residues (K5mut3). The shielding effect of acidic amino acids may explain why K5mut1 has higher activity. K5, K5mut1 and K5mut3 held characteristic β‐sheet spectrum while K5mut2 adopted random coil structure. These results suggest that K5mut1 with high efficacy is the minimal active peptide sequence of K5 and may have therapeutic potential in liver cancer.     

Mass spectrometry unravels disulfide bond formation as the mechanism that activates a molecular chaperone

The heat shock protein Hsp33 is a very potent molecular chaperone with a distinctive mode of functional regulation; its activity is redox-regulated. In its reduced form all six cysteinyl residues of Hsp33 are present as thiols, and Hsp33 displays no folding helper activity. Exposure of Hsp33 to oxidizing conditions like H(2)O(2), however, rapidly converts Hsp33 into an efficient molecular chaperone. Activated Hsp33 binds tightly to refolding intermediates of chemically denatured luciferase and suppresses efficiently their aggregation in vitro. Matrix-assisted laser desorption/ionization-mass spectrometry peptide mapping in combination with in vitro and on target protein chemical modification showed that this activation process of Hsp33 is accompanied by the formation of two intramolecular disulfide bonds within Hsp33: Cys(232)-S-S-Cys(234) and Cys(265)-S-S-Cys(268). Cys(141), although not involved in disulfide bond formation, was found highly reactive toward chemical modifications. In contrast, Cys(239) is readily accessible under reducing conditions but becomes poorly accessible though still reduced when Hsp33 is in its active state. This indicates a significant conformational change during the activation process of Hsp33. Mass spectrometry, thus, unraveled a novel molecular mechanism by which alteration of the disulfide bond structure, as a result of changes in the cellular redox potential, results in the activation of a molecular chaperone.     

Modification of human placental lactogen with plasmin. Preparation and characterization of a modified hormone with increased biologic activity.

To determine the structure needed for the biologic activity of human placental lactogen (hPL), we have cleaved hPL with the proteolytic enzyme plasmin. Plasmin modified hPL (PL-hPL) was purified by gel chromatography. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis before and after reduction showed that cleavage had occurred within the Cys53-Cys165 loop and tryptic peptide maps revealed that a single peptide consisting of residues 135 to 140 had been removed. 5-Dimethylaminonaphthalene-1-sulfonyl end group analysis and digestion with carboxypeptidase B confirmed that cleavage was complete and only the single hexapeptide was removed. In a membrane binding assay for lactogenic activity PL-hPL was 2- to 3-fold more potent than hPL. Using growth hormone receptors from rabbit liver membranes, PL-hPL was also more potent than hPL, but still much less potent than growth hormone. The lactogenic activity of PL-hPL in an in vitro bioassay was 75% above that of unmodified hormone. It is concluded that plasmin cleaves homologous peptides from hPL and growth hormone and that removal of the hexapeptide from hPL results in enhanced biologic activity.     

Batroxostatin, an Arg-Gly-Asp-containing peptide from Bothrops atrox, is a potent inhibitor of platelet aggregation and cell interaction with fibronectin

A potent inhibitor of platelet aggregation and cell adhesion was isolated from the venom of Bothrops atrox. This peptide, referred to as batroxostatin, was composed of 71 amino acids and showed a high degree of homology with other snake venom peptides including trigramin, albolabrin, elegantin and applagin: all 12 cysteines and the RGD sequence (standard one-letter amino acid codes) aligned in the same position. Compared on a molar basis, the anti-platelet aggregation activity of batroxostatin was about 1000-times higher than that of RGDS. In addition, batroxostatin was about 400-times more potent than GRGDS at inhibiting melanoma cell adhesion to fibronectin. Batroxostatin covalently attached to plastic promoted adhesion of melanoma cells. The anti-GP140 antibody, recognizing beta 1 integrins, completely inhibited adhesion of mouse melanoma cells to batroxostatin. This observation, in addition to the inhibitory effect of batroxostatin on the adhesion of chick fibroblasts to fibronectin, suggests that batroxostatin interacts with integrins from both the beta 1 and beta 3 subfamilies.     

Screening of ACE-inhibitory peptides from a random peptide-displayed phage library using ACE-coupled liposomes

Angiotensin I converting enzyme (ACE)-inhibitory peptides were screened from a random peptide-displayed phage library using ACE-coupled liposomes. Among four kinds of inhibitory peptides selected by biopanning with two different elution strategies, a peptide (LSTLRSFCA) showed the highest inhibitory activity with an IC(50) value of 3microM. By measuring inhibitory activities of fragments of the peptide, it was found that the RSFCA region was a functional site to inhibit strongly the ACE catalytic activity, and particularly both Arg and Cys residues were essential for the strong inhibitory activity. The inhibitory activity of RRFCA was slightly increased, while that of the RSFRA, in which the Cys residue was replaced by Arg, was decreased to greater extent in comparison with the inhibitory activity of RSFCA. Taking into account the results obtained from the SPOT analysis, it was suggested that the Arg and Phe residues in RSFCA were important for a specific interaction with ACE, and the Cys residue inhibited the ACE activity. The cystein-based ACE-inhibitory peptides have not been isolated from processed food materials. These findings suggested that the biopanning method utilizing protein-coupled liposomes and random peptide libraries might have a possibility to screen new functional peptides that are not found in processed food materials.     

Purification and properties of a recombinant sulfur analog of murine selenium-glutathione peroxidase.

We previously constructed plasmids for synthesis of glutathione-peroxidase (GPx) mutants in an Escherichia coli expression system. In these recombinant proteins either cysteine ([Cys]GPx mutant) or serine ([Ser]GPx mutant) were present in place of the active-site selenocysteine (SeCys) of the natural enzyme. We have now investigated GPx activity of [Cys]GPx and [Ser]GPx mutants. Enzyme assays performed on preparations of these partially purified proteins demonstrated that the [Cys]GPx mutant exhibited a significant GPx activity, unlike the [Ser]GPx mutant. Purification of [Cys]GPx was performed in two steps of ion-exchange chromatography giving a 98% homogenous protein in 50% yield. The purified [Cys]GPx protein was shown to be a symmetrical tetramer by the means of gel-filtration HPLC and SDS/PAGE. Two isoelectric points were found (6.8 and 7.2) which may reflect two different oxidation states of the mutant protein. The GPx activity of the [Cys]GPx mutant was optimal at pH 8.5. The [Cys]GPx mutant had a specific activity approximately 1000-fold smaller than that of the natural enzyme, and was very easily inactivated by hydroperoxides. Inhibition of the activity with iodoacetate determined a pKa of 8.3, presumably that of the active-site cysteine. Unlike that of SeGPx, the GPx activity of [Cys]GPx was only slightly inhibited by mercaptosuccinate. We discuss hypothetical mechanistic constraints of either catalytic cycle, which may explain such results.     

2-chloro-3-substituted-1,4-naphthoquinone inactivators of human cytomegalovirus protease.

A random screening approach has identified 2-chloro-3-substituted-1,4-naphthoquinones as potent inactivators of HCMV protease. Enzyme inactivation is due to modification of Cys202. Two of the most potent compounds maintain activity against HCMV in a plaque reduction assay.     

A single mutation within a Ca binding loop increases proteolytic activity,thermal stability,and surfactant stability

We improved the enzymatic properties of the oxidatively stable alkaline serine protease KP-43 through protein engineering to make it more suitable for use in laundry detergents. To enhance proteolytic activity, the gene encoding KP-43 was mutagenized by error-prone PCR. Screening identified a Tyr195Cys mutant enzyme that exhibited increased specific activity toward casein between pH 7 and 11. At pH 10, the mutant displayed 1.3-fold higher specific activity for casein compared to the wild-type enzyme, but the activity of the mutant was essentially unchanged toward several synthetic peptides. Furthermore, the Tyr195Cys mutation significantly increased thermal stability and surfactant stability of the enzyme under oxidizing conditions. Examination of the crystal structure of KP-43 revealed that Tyr195 is a solvent exposed residue that forms part of a flexible loop that binds a Ca^2 + ion. This residue lies 15–20 Å away from the residues comprising the catalytic triad of the enzyme. These results suggest that the substitution at position 195 does not alter the structure of the active center, but instead may affect a substrate–enzyme interaction. We propose that the Tyr195Cys mutation enhances the interaction with Ca^2 + and affects the packing of the Ca^2 + binding loop, consequently increasing protein stability. The simultaneously increased proteolytic activity, thermal stability, and surfactant stability of the Tyr195Cys mutant enzyme make the protein an ideal candidate for laundry detergent application.     

Cyclic melanotropins. Part VII: Modified ring structures--synthesis and biological activity

The highly potent cyclic analogue of alpha-MSH, Ac-[Cys4,Cys10]-alpha-MSH4-13-NH2, was structurally modified in position 4. Four analogues were prepared and their biological activities in the in vitro frog and lizard skin bioassays were determined. It was shown that removing the terminal acetylamino group to give [Mpa4,Cys10]-alpha-MSH4-13-NH2 resulted in little change in the biological activity, but a change in the stereochemistry of cysteine in position 4 to give Ac-[D-Cys4,Cys10[-alpha-MSH4-a3-NH2 led to a small decrease of activity in both bioassays. Decreasing the size of the intramolecular ring by removing one methylene group to give [Maa2,Cys10]-alpha-MSH4-13-NH2, resulted in an analogue with lower activities in both assays (about 3 times in the lizard and 500 times in the frog), and increasing the size of the righ by methylene group to give Ac-[Hcy4,Cys10]-alpha-MSH4-13-NH2 led to much lower activities in the lizard system and similar effects were seen upon decreasing the ring size in the frog skin assay.