| 9488652 |
A model for the mechanism of human topoisomerase I |
10.1126/science.279.5356.1534. |
Science |
A model for the mechanism of human topoisomerase I
Abstract
- The three-dimensional structure of a 70-kilodalton amino terminally truncated form of human topoisomerase I in complex with a 22-base pair duplex oligonucleotide, determined to a resolution of 2.8 angstroms, reveals all of the structural elements of the enzyme that contact DNA. The linker region that connects the central core of the enzyme to the carboxyl-terminal domain assumes a coiled-coil configuration and protrudes away from the remainder of the enzyme. The positively charged DNA-proximal surface of the linker makes only a few contacts with the DNA downstream of the cleavage site. In combination with the crystal structures of the reconstituted human topoisomerase I before and after DNA cleavage, this information suggests which amino acid residues are involved in catalyzing phosphodiester bond breakage and religation. The structures also lead to the proposal that the topoisomerization step occurs by a mechanism termed "controlled rotation."
|
| 9489702 |
LAT: the ZAP-70 tyrosine kinase substrate that links T cell receptor to cellular activation |
10.1016/s0092-8674(00)80901-0. |
Cell |
LAT: the ZAP-70 tyrosine kinase substrate that links T cell receptor to cellular activation
Abstract
- Despite extensive study, several of the major components involved in T cell receptor-mediated signaling remain unidentified. Here we report the cloning of the cDNA for a highly tyrosine-phosphorylated 36-38 kDa protein, previously characterized by its association with Grb2, phospholipase C-gamma1, and the p85 subunit of phosphoinositide 3-kinase. Deduced amino acid sequence identifies a novel integral membrane protein containing multiple potential tyrosine phosphorylation sites. We show that this protein is phosphorylated by ZAP-70/Syk protein tyrosine kinases leading to recruitment of multiple signaling molecules. Its function is demonstrated by inhibition of T cell activation following overexpression of a mutant form lacking critical tyrosine residues. Therefore, we propose to name the molecule LAT-linker for activation of T cells.
|
| 9510906 |
Roseocardin, a novel cardiotonic cyclodepsipeptide from Trichothecium roseum TT103 |
10.7164/antibiotics.50.1007. |
J Antibiot (Tokyo) |
Roseocardin, a novel cardiotonic cyclodepsipeptide from Trichothecium roseum TT103
Abstract
- A new cyclodepsipeptide, designated roseocardin, was isolated from the culture broth of Trichothecium roseum TT103. Roseotoxin B and destruxins A and B were also isolated during the same procedure. The structure of roseocardin was determined by EI-MS, NMR and X-ray crystallographic analysis. Roseocardin as well as the other cyclodepsipeptides were shown to produce positive inotropic effects on rat heart muscles.
|
| 9511906 |
Seven new microcystins possessing two L-glutamic acid units, isolated from Anabaena sp. strain 186 |
10.1021/tx970120t. |
Chem Res Toxicol |
Seven new microcystins possessing two L-glutamic acid units, isolated from Anabaena sp. strain 186
Abstract
- Electrospray ionization mass spectrometry has been applied to the structure assignment of seven new microcystins (1-7), obtained from cultured Anabaena sp. strain 186. The seven new microcystins contain the dehydroalanine (Dha) or L-Ser unit instead of the N-methyldehydroalanine unit and the L-Glu and/or its delta-methyl ester E(OMe) units at the two variable L-amino acid units, and the structures were assigned as Dha7microcystin-E(OMe)E(OMe) (1), D-Asp3,Dha7microcystin-E(OMe)E(OMe) (2), L-Ser7microcystin-E(OMe)E(OMe) (3), D-Asp3,L-Ser7microcystin-E(OMe)E(OMe) (4), Dha7microcystin-EE(OMe) (5), D-Asp3,Dha7microcystin-EE(OMe) (6), and L-Ser7microcystin-EE(OMe) (7). These microcystins are the first examples containing dicarboxylic amino acids at the two variable L-amino acid units in microcystins.
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| 9514014 |
Destruxin-A4 chlorohydrin, a novel destruxin from fungus OS-F68576: isolation, structure determination, and biological activity as an inducer of erythropoietin |
10.1021/np970475c. |
J Nat Prod |
Destruxin-A4 chlorohydrin, a novel destruxin from fungus OS-F68576: isolation, structure determination, and biological activity as an inducer of erythropoietin
Abstract
- In the course of screening for small-molecule modulators of erythropoietin gene expression, five destruxins were isolated from the fungal culture of OS-F68576. The structures were elucidated by extensive 1H and 13C NMR spectroscopy and by hydrolytic modification. One compound (destruxin-A4 chlorohydrin, 1) is a novel destruxin. All these compounds induced erythropoietin gene expression 5-fold at concentration of 0.2-2 microM.
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| 9521752 |
Three-dimensional solution structure of lactoferricin B, an antimicrobial peptide derived from bovine lactoferrin |
10.1021/bi972323m. |
Biochemistry |
Three-dimensional solution structure of lactoferricin B, an antimicrobial peptide derived from bovine lactoferrin
Abstract
- The solution structure of bovine lactoferricin (LfcinB) has been determined using 2D 1H NMR spectroscopy. LfcinB is a 25-residue antimicrobial peptide released by pepsin cleavage of lactoferrin, an 80 kDa iron-binding glycoprotein with many immunologically important functions. The NMR structure of LfcinB reveals a somewhat distorted antiparallel beta-sheet. This contrasts with the X-ray structure of bovine lactoferrin, in which residues 1-13 (of LfcinB) form an alpha-helix. Hence, this region of lactoferricin B appears able to adopt a helical or sheetlike conformation, similar to what has been proposed for the amyloidogenic prion proteins and Alzheimer's beta-peptides. LfcinB has an extended hydrophobic surface comprised of residues Phe1, Cys3, Trp6, Trp8, Pro16, Ile18, and Cys20. The side chains of these residues are well-defined in the NMR structure. Many hydrophilic and positively charged residues surround the hydrophobic surface, giving LfcinB an amphipathic character. LfcinB bears numerous similarities to a vast number of cationic peptides which exert their antimicrobial activities through membrane disruption. The structures of many of these peptides have been well characterized, and models of their membrane-permeabilizing mechanisms have been proposed. The NMR solution structure of LfcinB may be more relevant to membrane interaction than that suggested by the X-ray structure of intact lactoferrin. Based on the solution structure, it is now possible to propose potential mechanisms for the antimicrobial action of LfcinB."
|
| 9526566 |
A backbone-cyclic, receptor 5-selective somatostatin analogue: synthesis, bioactivity, and nuclear magnetic resonance conformational analysis |
10.1021/jm970633x. |
J Med Chem |
A backbone-cyclic, receptor 5-selective somatostatin analogue: synthesis, bioactivity, and nuclear magnetic resonance conformational analysis
Abstract
- Cyclo(PheN2-Tyr-D-Trp-Lys-Val-PheC3)-Thr-NH2 (PTR 3046), a backbone-cyclic somatostatin analogue, was synthesized by solid-phase methodology. The binding characteristics of PTR 3046 to the different somatostatin receptors, expressed in CHO cells, indicate high selectivity to the SSTR5 receptor. PTR 3046 is highly stable against enzymatic degradation as determined in vitro by incubation with rat renal homogenate and human serum. The biological activity of PTR 3046 in vivo was determined in rats. PTR 3046 inhibits bombesin- and caerulein-induced amylase and lipase release from the pancreas without inhibiting growth hormone or glucagon release. The major conformation of PTR 3046 in CD3OH, as determined by NMR, is defined by a type II' beta-turn at D-Trp-Lys and a cis amide bond at Val-PheC3."
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| 9531047 |
Enhancement of fibrinolysis by plactins: structure-activity relationship and effects in human U937 cells and in mice |
None |
Thromb Haemost |
Enhancement of fibrinolysis by plactins: structure-activity relationship and effects in human U937 cells and in mice
Abstract
- Plactin D, a cyclic pentapeptide cyclo(-D-Val-L-Leu-D-Leu-L-Phe-D-Arg-) produced by a fungal strain, enhances fibrinolytic activity (6). The present study deals with the structure-activity relationship of plactins and their effects in U937 cells and mice. The results obtained from 50 plactin D analogues with a single amino acid substitution demonstrated that the following substitutions were detrimental: the enantiomer for each of the five residues; a polar, an acidic or a basic residue for D-Val, L-Leu, D-Leu or L-Phe; a polar, a hydrophobic or an acidic residue for D-Arg. On the other hand, a compound with L-Leu or L-Val in place of L-Phe was seven times as active as plactin D. These results suggest an essential role of a sterically restricted arrangement of four hydrophobic residues and the adjacent basic residue. The enhancement of fibrinolysis was dependent on plasma, ranging from 2- to 3-fold when U937 cells were incubated with 15-30 microM plactin D in the presence of 6-50% plasma, while no elevation was observed when cells were incubated in the absence of plasma. Plasminogen alone could not substitute for plasma. The plactin D effect was totally abolished by anti-urokinase IgG but not by anti-tissue plasminogen activator IgG. Plactin D caused a plasma-dependent, transient increase in the cellular urokinase activity. This urokinase activation may have accounted for the increased fibrinolytic activity of plactin D-treated U937 cells. Homogenates of the lung obtained from mice 0.5 to 2 h after intravenous plactin D (5 mg/kg) showed 2- to 3-fold increased levels of fibrinolytic activity, while activities of the brain, heart, liver, spleen, kidney and aorta were not significantly affected. In conclusion, plactin D enhances fibrinolysis both in cultured mammalian cells and in experimental animals.
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| 9531419 |
The contryphans, a D-tryptophan-containing family of Conus peptides: interconversion between conformers |
10.1111/j.1399-3011.1998.tb01213.x. |
J Pept Res |
The contryphans, a D-tryptophan-containing family of Conus peptides: interconversion between conformers
Abstract
- We previously characterized contryphan-R, a D-tryptophan-containing octapeptide from the venom of Conus radiatus. In this study, we present evidence that the contryphan family of peptides is widely distributed in venoms of the fish-hunting cone snails. We purified, synthesized and characterized contryphan-Sm from Conus stercusmuscarum venom, and obtained molecular evidence for the existence of a third peptide, contryphan-P from Conus purpurascens venom ducts. The sequences of these three contryphans showed identity in seven of eight amino acids and a conserved pattern of post-translational modification. We also demonstrate that contryphan-Sm equilibrates between two distinct conformational states.
|
| 9533644 |
Role of different bombesin receptor subtypes mediating contractile activity in cat upper gastrointestinal tract |
10.1016/s0196-9781(97)00467-1. |
Peptides |
Role of different bombesin receptor subtypes mediating contractile activity in cat upper gastrointestinal tract
Abstract
- Mammalian bombesin-like peptides, gastrin-releasing peptide (GRP) and neuromedin B (NMB) are known to increase the motility of different segments in the gut. The present study was carried out to identify the bombesin receptor subtypes mediating the contractions induced by exogenous bombesin-like peptides in muscle strips isolated from cat esophagus, fundus, and duodenum. Both GRP-10 and NMB evoked concentration-dependent contractions in circular strips of esophagus and fundus and in longitudinal strips of the duodenum. These contractions were tetrodotoxin- and atropine-resistant. The potency of NMB in esophageal strips was 33 times higher than that of GRP-10. The NMB-preferring receptor antagonists D-Nal-Cys-Tyr-D-Trp-Lys-Val-Cys-Nal-NH2 (SSocta) and D-Nal-cycloCys-Tyr-D-Trp-Orn-Val-Cys-Nal-NH2 (BIM-23127) shifted the NMB and GRP concentration-response curves to the right, while the GRP-preferring receptor antagonist D-Phe6Bombesin(6-13)-methyl-ester (BME) did not affect the response to the peptides. Isolated muscle strips from the cat fundus and duodenum showed a higher sensitivity to GRP-10 than to NMB. In both segments, BME shifted the GRP-10 and NMB concentration-response curves to the right, while SSocta had no effect. The antagonism of BME was competitive on duodenal but not competitive on fundic muscle. We conclude that the direct myogenic action of GRP-10 and NMB in the esophagus is mediated mainly via NMB-preferring receptors, while GRP-preferring receptors are responsible for the contractile responses to bombesin-like peptides in feline fundus and duodenum. Our data suggest that the GRP receptor population located on fundic muscle might be nonhomogeneous.
|
| 9534862 |
Selective alpha v beta 3 integrin blockade potently limits neointimal hyperplasia and lumen stenosis following deep coronary arterial stent injury: evidence for the functional importance of integrin alpha v beta 3 and osteopontin expression during neointima formation |
10.1016/s0008-6363(97)00184-3. |
Cardiovasc Res |
Selective alpha v beta 3 integrin blockade potently limits neointimal hyperplasia and lumen stenosis following deep coronary arterial stent injury: evidence for the functional importance of integrin alpha v beta 3 and osteopontin expression during neointima formation
Abstract
- Lumen loss from vascular restenosis remains a leading cause of chronic revascularization failure.\n \n \n \n \n We hypothesized that cell-matrix adhesion, migration, and differentiation events that underlie restenosis are mediated by alpha v beta 3 integrin-ligand interactions.\n \n \n \n \n Using immunohistochemistry and in situ hybridization, we examined the spatial and temporal vessel wall expression of alpha v beta 3 and osteopontin following deep coronary arterial injury. Cell migration and adhesion assays were performed to demonstrate the affinity and specificity of XJ 735 for various vessel wall integrins. The effects of XJ 735 (a selective cyclic Arg-Gly-Asp (RGD) peptidomimetic alpha v beta 3 antagonist) on neointimal hyperplasia and lumen stenosis were tested in a porcine coronary injury model. Normolipemic swine underwent oversized stent injury followed by XJ 735 administration (9 animals, 28 lesions; 1 mg/kg bolus + 7 days 4 mg/kg/d infusion + 21 days 2 mg/kg i.v. bolus 12 hourly) or placebo (10 animals, 30 arterial lesions).\n \n \n \n \n Maximal alpha v beta 3 immunoreactivity was observed between 7-14 days following injury in the neointima, media, and adventitia. Maximal osteopontin mRNA signal in the neointima, media, and adventitia was observed at 14, 7 and 28 days respectively. IC50 for XJ 735 alpha v beta 3-mediated inhibition of human and porcine endothelial cell adhesion, and vascular smooth muscle cell migration, ranged from 0.6 to 4.4 microM. In contrast, IC50 for porcine or human alpha IIb/beta 3, alpha 4 beta 1, alpha v beta 5, and alpha 5 beta 1 inhibition exceeded 100 microM. Steady state XJ 735 plasma levels exceeded 5 microM. Despite slightly higher injury scores in XJ 735 treated animals, significant reductions in mean neointima area (43% reduction; p = 0.0009), and mean percent lumen stenosis (approximately 2.9 fold reduction; p = 0.04) were observed in XJ 735 treated animals. XJ 735 treatment did not significantly alter the relative size of the arterial injury and reference sites (geometric remodeling). Comparison of neontima area vs. injury score regression lines revealed significant reductions in slope (p = 0.0001) and intercept (p = 0.0001) for XJ 735.\n \n \n \n \n Selective alpha v beta 3 blockade is an effective anti-restenosis strategy that potently limits neointimal growth and lumen stenosis following deep arterial injury. The co-ordinate spatial and temporal upregulation of alpha v beta 3 expression following vessel wall injury, and the high affinity and specificity of XJ 735 for alpha v beta 3, confirms the importance of this integrin in adhesive and migratory cell-matrix events underlying coronary restenosis.
|
| 9535998 |
Novel somatostatin analogs for the treatment of acromegaly and cancer exhibit improved in vivo stability and distribution |
None |
J Pharmacol Exp Ther |
Novel somatostatin analogs for the treatment of acromegaly and cancer exhibit improved in vivo stability and distribution
Abstract
- The biodistribution of several radiolabeled somatostatin (SRIF) analogs was determined in the rat. Newly developed analogs BIM-23190 and BIM-23197 attained higher plasma levels and much greater target tissue concentrations than the clinically used BIM-23014 analog. Highest tissue concentrations of BIM-23190 and BIM-23197 were found in adrenal, kidney, pituitary and pancreas, tissues that are known to be abundant in mRNA for the somatostatin subtype 2 receptor. BIM-23190 and BIM-23197 associated radioactivity in these tissues was prolonged compared with that of BIM-23014, especially in the SRIF-receptor-rich pituitary. BIM-23190 and BIM-23197 were more stable in vivo and much less subject to biliary excretion than BIM-23014. These properties account for the elevated plasma and target tissue concentrations of these new SRIF analogs. Based on higher plasma levels, greater distribution to target tissues and longer in vivo stability, BIM-23190 and BIM-23197 may prove to be superior to BIM-23014 for the treatment of acromegaly and some types of cancer.
|
| 9541023 |
A somatostatin receptor 1 selective ligand inhibits Ca2+ currents in rat insulinoma 1046-38 cells |
10.1016/s0014-5793(98)00221-x. |
FEBS Lett |
A somatostatin receptor 1 selective ligand inhibits Ca2+ currents in rat insulinoma 1046-38 cells
Abstract
- Rat insulinoma 1046-38 cells represent a model system to study beta-cell function. The mRNAs for sst1 and sst2, two of the five somatostatin receptors, were detected by reverse transcription polymerase chain reaction amplification in these cells. Displacement binding analysis suggested that sstl represents the major somatostatin receptor subtype. The sstl selective compound CH-275 did not inhibit adenylyl cyclases while compounds that activated sst2 did. In contrast, CH-275 caused a marked inhibition of voltage-operated Ca2+ channels while the sst2 specific analog octreotide elicited a less pronounced effect suggesting that in rat insulinoma 1046-38 cells sst1 preferably mediates the inhibition of Ca2+ channels.
|
| 9548884 |
Synthesis and Stereochemistry of Axinastatin 4 |
10.1021/np970139w. |
J Nat Prod |
Synthesis and Stereochemistry of Axinastatin 4
Abstract
- Axinastatin 4 from a marine sponge was synthesized by high-dilution BOP-Cl cyclization of Trp-Val-Pro-Leu-Thr-Pro-Leu in 94% yield (only 2.5% at normal dilution), showing the configurations of the last three amino acids to be S. Synthetic axinastatin 4 was devoid of cytostatic activity.
|
| 9553137 |
Characterization of insulin receptor substrate 4 in human embryonic kidney 293 cells |
10.1074/jbc.273.17.10726. |
J Biol Chem |
Characterization of insulin receptor substrate 4 in human embryonic kidney 293 cells
Abstract
- We recently cloned IRS-4, a new member of the insulin receptor substrate (IRS) family. In this study we have characterized IRS-4 in human embryonic kidney 293 cells, where it was originally discovered. IRS-4 was the predominant insulin-elicited phosphotyrosine protein in these cells. Subcellular fractionation revealed that about 50% of IRS-4 was located in cellular membranes, and immunofluorescence indicated that IRS-4 was concentrated at the plasma membrane. Immunoelectron microscopy conclusively established that a large portion of the IRS-4 was located at the cytoplasmic surface of the plasma membrane in both the unstimulated and insulin-treated states. IRS-4 was found to be associated with two src homology 2 (SH2) domain-containing proteins, phosphatidylinositol 3-kinase and Grb2, the adaptor to the guanine nucleotide exchange factor for Ras. On the other hand, no significant association was detected with two other SH2 domain proteins, the SH2-containing protein tyrosine phosphatase 2 and phospholipase Cgamma. Insulin-like growth factor I acting through its receptor was as effective as insulin in eliciting tyrosine phosphorylation of IRS-4, but interleukin 4 and epidermal growth factor were ineffective.
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