On the nucleation and growth of amyloid beta-protein fibrils: detection of nuclei and quantitation of rate constants

We have studied the fibrillogenesis of synthetic amyloid beta-protein-(1-40) fragment (A beta) in 0.1 M HCl. At low pH, A beta formed fibrils at a rate amenable to detailed monitoring by quasi-elastic light-scattering spectroscopy. Examination of the fibrils with circular dichroism spectroscopy and electron microscopy showed them to be highly similar to those found in amyloid plaques. We determined the hydrodynamic radii of A beta aggregates during the entire process of fibril nucleation and growth. Above an A beta concentration of approximately 0.1 mM, the initial rate of elongation and the final size of fibrils were independent of A beta concentration. Below an A beta concentration of 0.1 mM, the initial elongation rate was proportional to the peptide concentration, and the resulting fibrils were significantly longer than those formed at higher concentration. We also found that the surfactant n-dodecylhexaoxyethylene glycol monoether (C12E6) slowed nucleation and elongation of fibrils in a concentration-dependent manner. Our observations are consistent with a model of A beta fibrillogenesis that includes the following key steps: (i) peptide micelles form above a certain critical A beta concentration, (ii) fibrils nucleate within these micelles or on heterogeneous nuclei (seeds), and (iii) fibrils grow by irreversible binding of monomers to fibril ends. Interpretation of our data enabled us to determine the sizes of fibril nuclei and A beta micelles and the rates of fibril nucleation (from micelles) and fibril elongation. Our approach provides a powerful means for the quantitative assay of A beta fibrillogenesis.

Structure of von Willebrand factor-cleaving protease (ADAMTS13), a metalloprotease involved in thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura is associated with acquired or congenital deficiency of a plasma von Willebrand factor-cleaving protease (VWFCP). Based on partial amino acid sequence, VWFCP was identified recently as a new member of the ADAMTS family of metalloproteases and designated ADAMTS13. The 4.6-kilobase pair cDNA sequence for VWFCP has now been determined. By Northern blotting, full-length VWFCP mRNA was detected only in liver. VWFCP consists of 1427 amino acid residues and has a signal peptide, a short propeptide terminating in the sequence RQRR, a reprolysin-like metalloprotease domain, a disintegrin-like domain, a thrombospondin-1 repeat, a Cys-rich domain, an ADAMTS spacer, seven additional thrombospondin-1 repeats, and two CUB domains. VWFCP apparently is made as a zymogen that requires proteolytic activation, possibly by furin intracellularly. Sites for Zn(2+) and Ca(2+) ions are conserved in the protease domain. The Cys-rich domain contains an RGDS sequence that could mediate integrin-dependent binding to platelets or other cells. Alternative splicing gives rise to at least seven potential variants that truncate the protein at different positions after the protease domain. Alternative splicing may have functional significance, producing proteins with distinct abilities to interact with cofactors, connective tissue, platelets, and von Willebrand factor.

Record high hole mobility in polymer semiconductors via side-chain engineering

Charge carrier mobility is still the most challenging issue that should be overcome to realize everyday organic electronics in the near future. In this Communication, we show that introducing smart side-chain engineering to polymer semiconductors can facilitate intermolecular electronic communication. Two new polymers, P-29-DPPDBTE and P-29-DPPDTSE, which consist of a highly conductive diketopyrrolopyrrole backbone and an extended branching-position-adjusted side chain, showed unprecedented record high hole mobility of 12 cm(2)/(V·s). From photophysical and structural studies, we found that moving the branching position of the side chain away from the backbone of these polymers resulted in increased intermolecular interactions with extremely short π-π stacking distances, without compromising solubility of the polymers. As a result, high hole mobility could be achieved even in devices fabricated using the polymers at room temperature.

Purification of human von Willebrand factor-cleaving protease and its identification as a new member of the metalloproteinase family

von Willebrand factor (vWF) is synthesized in megakaryocytes and endothelial cells as a very large multimer, but circulates in plasma as a group of multimers ranging from 500 to 10 000 kd. An important mechanism for depolymerization of the large multimers is the limited proteolysis by a vWF-cleaving protease present in plasma. The absence or inactivation of the vWF-cleaving protease results in the accumulation of large multimers, which may cause thrombotic thrombocytopenic purpura. The vWF-cleaving protease was first described as a Ca(++)-dependent proteinase with an apparent molecular weight of approximately 300 kd. Thus far, however, it has not been isolated and characterized. In this study, the purification of human vWF-cleaving protease from a commercial preparation of factor VIII/vWF concentrate by means of several column chromatographic steps, including 2 steps of heparin-Sepharose column, is reported. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the anion exchange and gel filtration column fractions showed that the vWF-cleaving protease activity corresponded to a protein band of 150 kd. After reduction, it migrated with an apparent weight of 190 kd. The amino terminal sequence of the 150-kd band was AAGGIL(H)LE(L)L(D)AXG(P)X(V)XQ (single-letter amino acid codes), with the tentative residues shown in parentheses. A search of the human genome sequence identified the vWF-cleaving protease as a new member of the ADAMTS (a disintegrin and metalloproteinase with thrombospondin type I motif) family of metalloproteinase. An active site sequence of HEIGHSFGLEHE (single-letter amino acid codes) was located at 150 residues from the N terminus of the protein.

Band-like transport, high electron mobility and high photoconductivity in all-inorganic nanocrystal arrays

Flexible, thin-film electronic and optoelectronic devices typically involve a trade-off between performance and fabrication cost. For example, solution-based deposition allows semiconductors to be patterned onto large-area substrates to make solar cells and displays, but the electron mobility in solution-deposited semiconductor layers is much lower than in semiconductors grown at high temperatures from the gas phase. Here, we report band-like electron transport in arrays of colloidal cadmium selenide nanocrystals capped with the molecular metal chalcogenide complex In(2)Se(4)(2-), and measure electron mobilities as high as 16 cm(2) V(-1) s(-1), which is about an order of magnitude higher than in the best solution-processed organic and nanocrystal devices so far. We also use CdSe/CdS core-shell nanoparticles with In(2)Se(4)(2-) ligands to build photodetectors with normalized detectivity D* > 1 × 10(13) Jones (I Jones = 1 cm Hz(1/2) W(-1)), which is a record for II-VI nanocrystals. Our approach does not require high processing temperatures, and can be extended to different nanocrystals and inorganic surface ligands.

Isolation and structure of an untriakontapeptide with opiate activity from camel pituitary glands

The isolation of an untriakontapeptide from camel pituitary extracts has been described. Its structure has been determined and shown to be identical to the sequence of carboxyl-terminal 31 amino acids of ovine beta-lipotropin. The peptide possesses very low lipotropic activity but significant opiate activity.

pRb controls proliferation, differentiation, and death of skeletal muscle cells and other lineages during embryogenesis

Mice deficient for the RB gene (RB-/-), prior to death at embryonic day 14.5, show increased cell death in all tissues that normally express RB1: the nervous system, liver, lens, and skeletal muscle precursor cells. We have generated transgenic mice (RBlox) that express low levels of pRb, driven by an RB1 minigene. RBlox/RB-/- mutant fetuses die at birth with specific skeletal muscle defects, including increased cell death prior to myoblast fusion, shorter myotubes with fewer myofibrils, reduced muscle fibers, accumulation of elongated nuclei that actively synthesized DNA within the myotubes, and reduction in expression of the late muscle-specific genes MCK and MRF4. Thus, insufficient pRb results in failure of myogenesis in vivo, manifest in two ways. First, the massive apoptosis of myoblasts implicates a role of pRb in cell survival. Second, surviving myotubes failed to develop normally and accumulated large polyploid nuclei, implicating pRb in permanent withdrawal from the cell cycle. These results demonstrate a role for pRb during terminal differentiation of skeletal muscles in vivo and place pRb at a nodal point that controls cell proliferation, differentiation, and death.

Elastic free energy of anisotropic helical ribbons as metastable intermediates in the crystallization of cholesterol

We report measurements of the geometrical structure and temporal evolution of metastable helical intermediates in the pathway for cholesterol crystallization in native and model biles. We find that the lecithin component in the bile can dramatically affect the kinetics along this pathway. We also present a theoretical description of these helical intermediates using an elastic free energy appropriate for anisotropic bilayers of tilted chiral amphiphiles, which provides a quantitative description of the observed helical ribbon geometry and insight into the relative free energies of the observed metastable intermediates.

Effect of selenophene in a DPP copolymer incorporating a vinyl group for high-performance organic field-effect transistors

A new polymeric semiconductor, PDPPDTSE, is reported which is composed of a diketopyrrolopyrrole moiety and selenophenylene vinylene selenophene, with a high field-effect mobility achieved through intermolecular donor-acceptor interactions. The field-effect mobility of OFET devices based on PDPPDTSE by spin-casting is 4.97 cm(2) V(-1) s(-1) , which is higher than predecessor polymeric semiconductors.

Comparison of oral iron chelator L1 and desferrioxamine in iron-loaded patients

The efficacy of the oral iron chelator 1,2-dimethyl-3-hydroxypyrid-4-one (L1) was compared with that of subcutaneous desferrioxamine in 26 patients with transfusional iron overload. Immediately after red-cell transfusion, 20 patients were randomised to receive either desferrioxamine (50 mg/kg daily as a 12 h subcutaneous infusion), or L1 (50 mg/kg daily by mouth). Patients were evaluated during treatment with the other drug after transfusion the next month. Mean (SD) daily urinary iron excretion was lower during L1 than during desferrioxamine (12.3 [6.7] vs 18.2 [15.3] mg/day). In 5 patients the dose of L1 was raised from 50 to 75 mg/kg daily; mean urinary iron excretion rose from 13.8 (7.0) mg/day to 26.7 (17.8) mg/day, comparable with that during desferrioxamine (24.9 [24.3] mg/day). Faecal iron excretion rose slightly over baseline in 6 patients studied during L1 administration (from 8.5 [0.9] mg/day to 12.2 [0.9] mg/day). Pharmacokinetic studies showed an elimination half-life for L1 of 117-237 min. Studies in dogs and in volunteers showed no absorption of the L1-iron complex, excluding a contribution of absorption of intraluminal complexes of L1 and food iron to urinary iron excretion. Further animal toxicity testing is needed before L1 can be studied in a broader group of patients.

Filamentous, helical, and tubular microstructures during cholesterol crystallization from bile. Evidence that cholesterol does not nucleate classic monohydrate plates

Precipitation of cholesterol in gallbladder bile is believed to produce platelike cholesterol monohydrate crystals directly. We report complementary time-lapse microscopic studies of cholesterol crystallization from model bile that reveal initial assembly of filamentous cholesterol crystals covered by a monomolecular layer of lecithin. Over a few days, the filaments evolved through needle, helical, and tubular microstructures to form classical platelike cholesterol monohydrate crystals. Similar crystallization phenomena were observed in human gallbladder biles from cholesterol but not pigment stone patients. Synchrotron x-ray diffraction of the earliest filaments suggested a cholesterol monohydrate polymorph or admixture with an anhydrous cholesterol precursor. However, density gradient centrifugation of filamentous crystals revealed that their density was 1.032 g/ml, consistent with anhydrous cholesterol. Conventional x-ray diffraction of transitional crystalline forms was consistent with pure cholesterol monohydrate crystals, as were the equilibrium platelike crystals. These novel findings suggest that crystalline cholesterol in bile may not be completely mature or hydrated initially, but undergoes a series of transformations to become thermodynamically stable monohydrate plates. These observations have important implications for understanding the control of cholesterol crystallization in bile, as well as explaining putative crystal cytotoxicity during gallstone formation.

Effect of metal ions on photoluminescence, charge transport, magnetic and catalytic properties of all-inorganic colloidal nanocrystals and nanocrystal solids

Colloidal semiconductor nanocrystals (NCs) provide convenient "building blocks" for solution-processed solar cells, light-emitting devices, photocatalytic systems, etc. The use of inorganic ligands for colloidal NCs dramatically improved inter-NC charge transport, enabling fast progress in NC-based devices. Typical inorganic ligands (e.g., Sn(2)S(6)(4-), S(2-)) are represented by negatively charged ions that bind covalently to electrophilic metal surface sites. The binding of inorganic charged species to the NC surface provides electrostatic stabilization of NC colloids in polar solvents without introducing insulating barriers between NCs. In this work we show that cationic species needed for electrostatic balance of NC surface charges can also be employed for engineering almost every property of all-inorganic NCs and NC solids, including photoluminescence efficiency, electron mobility, doping, magnetic susceptibility, and electrocatalytic performance. We used a suite of experimental techniques to elucidate the impact of various metal ions on the characteristics of all-inorganic NCs and developed strategies for engineering and optimizing NC-based materials.

Structure-activity analysis of a Conus peptide blocker of N-type neuronal calcium channels

The synthetic peptide SNX-111 corresponding to the sequence of the omega-conopeptide MVIIA from the venom of the marine snail Conus magus is a highly potent and selective antagonist of N-type calcium channels. We have synthesized and characterized a large number of analogs of SNX-111 in order to elucidate the structural features of the peptide involved in blocking N-type calcium channels. Comparison of the binding of SNX-111 and its analogs to rat brain synaptosomal membranes rich in N-type channels revealed that, among the four lysines and two arginines in the molecule, lysine in position 2 and arginines at position 10 and 21 are important for the interaction of SNX-111 with N-type channels. The importance of the middle segment from residues 9 through 14 for this binding interaction was revealed by substitution of the individual residues as well as by the construction of hybrid peptides in which the residues 9-12 in SNX-111 and another conopeptide, SNX-183, corresponding to a peptide SVIB from Conus striatus, were interchanged. Introduction of the sequence SRLM from SNX-111 in place of RKTS in position 9-12 in SNX-183 resulted in a 38-fold increase in affinity.

Soluble and Easily Crystallized Anthracene Derivatives: Precursors of Solution-Processable Semiconducting Molecules

New soluble anthracene derivatives containing thiophene and phenylenevinylene derivatives were synthesized via well-known synthetic routes. TIPS derivatives were added at the 9,10-positions of anthracene for the solubility and crystallinity. Both of the molecules were found to be promising for high charge mobility and stable organic semiconductors. The soluble anthracene core (TIPSAnt) is a potential precursor for the synthesis of novel semiconducting materials.

Plum coatings of lemongrass oil-incorporating carnauba wax-based nanoemulsion

Nanoemulsions containing lemongrass oil (LO) were developed for coating plums and the effects of the nanoemulsion coatings on the microbial safety and physicochemical storage qualities of plums during storage at 4 and 25 °C were investigated. The emulsions used for coating were produced by mixing a carnauba wax-based solution (18%, w/w) with LO at various concentrations (0.5% to 4.0%, w/w) using dynamic high pressure processing at 172 MPa. The coatings were evaluated for their ability to inhibit the growth of Salmonella Typhimurium and Escherichia coli O157:H7 and their ability to preserve various physicochemical qualities of plums. Uniform and continuous coatings on plums, formed with stable emulsions, initially inhibited S. Typhimurium and E. coli O157:H7 by 0.2 to 2.8 and 0.8 to 2.7 log CFU/g, respectively, depending on the concentration of LO and the sequence of coating. The coatings did not significantly alter the flavor, fracturability, or glossiness of the plums. The antimicrobial effects of the coatings against S. Typhimurium and E. coli O157:H7 were demonstrated during storage at 4 and 25 °C. The coatings reduced weight loss and ethylene production by approximately 2 to 3 and 1.4 to 4.0 fold, respectively, and also retarded the changes in lightness and the concentration of phenolic compounds in plums during storage. The firmness of coated plums was generally higher than uncoated plums when stored at 4 °C and plum respiration rates were reduced during storage. Coatings containing nanoemulsions of LO have the potential to inhibit Salmonella and E. coli O157:H7 contamination of plums and may extend plum shelf life.

Interaction between trimethoprim-sulfamethoxazole and methotrexate in children with leukemia

Because trimethoprim-sulfamethoxazole (TMP-SMX) causes neutropenia in children with leukemia, we investigated the possibility that pharmacokinetic interaction between methotrexate (MTX) and TMP-SMX causes accumulation of the antileukemia agent. We studied the pharmacokinetics of MTX given intravenously or orally to nine children with acute lymphoblastic leukemia, once with and once without TMP-SMX. There was an increase in free MTX fraction during TMP-SMX therapy in all patients, from (mean +/- SD) 37.4 +/- 11% without TMP-SMX to 52.2 +/- 6.4% with TMP-SMX (p less than 0.01). Plasma clearance of total MTX did not change significantly, whereas clearance of free MTX decreased significantly (from 12.5 +/- 4 to 7.6 +/- 1.5 ml/kg/min; p less than 0.05). There was a consistent decrease in the renal clearance of free MTX (from 12.1 +/- 6.8 to 5.6 +/- 2.4 ml/kg/min; p less than 0.05). Elimination half-life of MTX was not affected significantly by TMP-SMX. There was a significant correlation between serum concentrations of TMP-SMX and the percentage of decrease in the renal clearance of free MTX (r = 0.91; p less than 0.05). These changes in protein binding and tubular clearance of MTX, caused by competition with TMP-SMX, result in a mean 66% increase in systemic exposure to MTX and may explain the myelotoxicity often observed with the coadministration of the two drugs.

Isolation, characterization, and amino acid sequence of melanotropins from camel pituitary glands

The isolation of two beta-melanotropins and two alpha-melanotropins from camel pituitary glands has been described, and their amino acid sequences have been determined. Two of them are identified as alpha-melanotropin and deacetylated alpha-melanotropin. There are also two beta-melanotropins whose structures are identical with the bovine hormone except that one has glycine in position 2 and the other glycine in position 2 as well as glutamine in position 8. The melanocyte-stimulating and lipolytic activities of these four camel melanotropins have been investigated by in vitro assay procedures.